Producer: Sina Technology "Science Everyone" Unread
Author: William M. C。 William C. Burger: Director of the Botanical Museum of the Chicago Museum of Nature, usa, has been committed to the research of biodiversity recombination and conservation for decades, especially good at using popular language to explain profound principles, helping non-biological readers better understand the operation of the biological world.
There is such an old terrier among biologists, saying that the famous British biologist J.B.S. Haldane attended a cocktail party where a bishop asked him a strange question in person. Since then, since the 1930s, whenever it comes to the diversity of life on Earth, this question and answer will surely be mentioned. The bishop's question went like this: "Dr. Haldane, you study biology, so what do you say about the nature of God?" Faced with such a big question, our great scientist replied without hesitation and directly: "God loves the Beetle!" ”
That's not true at all! I think the Creator just likes beetles (Coleoptera), otherwise why do you say there are so many kinds of them? According to 2006 statistics, about 380,000 species of beetles have been found. That is to say, it is quite laborious for students who study insects to define a new species, give them new Latin literary names, and match the specimens, and then write these results into a paper for publication. Nowadays, entomologists generally publish papers on new species with photographs and are accustomed to collecting specimens of new species (also known as pattern specimens) in public museums or university laboratories (pattern specimens are significant in naming animals and plants, and the name of a new species will be used to associate it with its type specimens). Different individuals of the same species may have differences, similar species may come together, and different people may have different understandings of language descriptions, so only pattern markers can accurately correspond to a scientific name). Entomologists around the world have worked tirelessly to reveal 380,000 different beetles for us. Compared with other organisms, there are about 5,500 species of mammals and more birds, about 10,000 species. Looking at the plant world, the earth is so rich in resources, with more than 310,000 species of land plants, and this is already a very conservative number, which also includes mosses, land money, ferns and their close relatives, as well as all kinds of conifers and more than 200,000 species of flowering plants. But all of these greenery together still can't match the number of beetles. Speaking of the animal world, there seem to be more species of beetles than all the non-microbial species in the ocean combined, and this already includes jellyfish, a variety of aquatic worms, all kinds of molluscs and various crabs, and thousands of species of fish. 380,000 species, I said, that's too much! To make matters worse, the number of this group is still growing. In the high canopy of the rainforest, and even in the soil around you, scientists are constantly discovering new, never-documented species.
Why are there so many types of beetles?
Aside from God's liking, what is the reason why the Beetle can have so many kinds? Like other biological questions, there are many answers to this question. The obvious reason is that the Beetles are very small. Even the largest beetle is about the same weight as a mouse, and the smallest is inferior to a fly. To show you a strong contrast – rhinos and elephants, the largest and heaviest terrestrial animals on Earth, are less than 10 species, because they each require several square kilometers of land to survive and reproduce. Beetles are different, and a few square meters is enough to make them a lifetime. From here you can see a law of the biological world, right? Both the number of species and the number of individuals of a creature are inversely proportional to the size of the organism. Obviously, the petite body shape allows for more beetles in the small space.
But its small size is just one of the reasons for the large variety of beetles. Beetles live in a variety of different habitats, and their habits vary widely. Most beetles live in temperate and tropical regions, with a small number surviving in tundra and alpine regions, while the polar regions do not have beetles. Akatsuki will invade your kitchen, beetles will destroy your blankets, and Japanese golden turtles will nibble on plants in your garden. On the warmer evenings of June, the June gill-horned golden turtles fly to the screens, while the fireflies give a bright signal in the evening. In addition to the huge number of species, some species of beetles are already in the thousands of species themselves.
In the western United States, ladybugs migrate to the mountains and gather together for the winter. In the early 20th century, anglers would go to the highs of California's Sierra Madre Mountains to collect these sleeping ladybirds and then sell them to farmers to control aphids (ladybug larvae and adults feed on aphids). Every winter throughout the 20th century, such insecticidal activities harvested tons of ladybugs (you read that right, tons). Calculate that there are about 44.344 million pieces per ton. That's too much. In fact, there are 380,000 species of beetles, and the number of each one may be as high as millions or even tens of millions, and it is not an exaggeration to say that the earth has kept tens of billions or even trillions of beetles. So, what is the secret of the Beetle family's prosperity?
In the long history of life, species extinction has always been a powerful destructive force. Countless fossil evidence suggests that about 98% of the life that once lived is extinct. Climate change, drought, disease pandemics and several major geological changes are difficulties that the vast majority of flora and fauna cannot overcome. So, seeing a family as successful as the Beetles, we can understand how adaptable they are to their environment. In fact, you only need to look at it to know one of their most conspicuous features - hardness. Through the leafy jungle, you may step on the beetles every step, but they can escape when you lift your feet. The hard exoskeletons take on the responsibility of protecting the soft body, and the Beetle's innovation is that they evolve a pair of forewings into a set of elytra wings, thus protecting its entire thorax and abdomen. In addition, the Beetle's body is also protected by "armor" at the front and back, and some species of Beetles even live like a mini tank. The "Volkswagen Beetle" car got its name precisely because it looks like some Beetles. Best of all, the beetle's hard elytra can also be lifted, allowing the hindwings that are really used for flight to spread out and fly. But while most beetles can fly, choosing to harden means they can't fly at the same time. This is why the large beetles are only active at night, as they need to avoid birds of prey that prey during the day. Flying and armor give the Beetle two huge advantages in the competition for survival, but the Beetle's advantages do not stop there.
The rough road to life
Beetles are insects that undergo four stages in their lifetime, and this insect is called a complete metamorphosis insect. The four stages of life of a fully metamorphic insect are completely independent and vary greatly. The first is the egg. This period is relatively short, or rather, it becomes a mere means for the Beetle to survive the harsh winter or dry season. At the right time, the eggs will be broken by the "little inhabitants" inside, the larvae. The larval stage is the next wonderful period in the life of a completely metamorphosed insect, during which the only task of the larvae is to eat and grow. Beetles have a variety of larvae, ranging from small worms to large fleshy worms that you find in soil and saprophytes, and many of them even prefer to prey on their own initiative. However, whether active or quiet, the significance of this stage of completely metamorphosed insects is to accumulate the necessary energy for future adults.
The beetles go through a separate stage from the fat flesh worm to the delicate adult worm - the pupalization period. Of all the fully metamorphosed insects, you're probably most familiar with butterfly or moth pupae. Inside the pupal shell, most of the larvae's body dissolves. You read that right, almost all the tissue in the pupa will liquefy, and then this liquid will be transformed by some special tissue inside the pupa, and eventually become a complete adult. If you think about it, this transformation process is nothing short of miraculous, and this is the key reason why many insects have an evolutionary advantage. The form of adult insects is completely different from that of larvae, they can fly, they can find the opposite sex to mate and reproduce, it is simply a makeover, life is completely new. In this sense, the beetle has two lifes: one is the larval stage, which is mainly responsible for eating, and the other is the mature adult stage, which is mainly responsible for travel and reproduction. That's a good thing. But there is also a serious flaw in this way of life cycle, that is, in the adult stage, the insect will no longer have any growth, and when it crawls out of the pupa, it will never grow again.
shell lang and burial worm
Another reason for the wide variety of beetles is that they have a world of different ways of living with each other, a feature that allows different species of beetles to live in the same habitat without interfering with each other. For example, a dung shell man, or dung beetle, will go out to look for fresh feces, and when found, a pair of dung beetles (dung beetle father and dung beetle mother) will tirelessly make feces into a round dung ball, and then roll the dung ball to a convenient burial place. This fecal ball will become a warm home and source of nutrition for dung beetle larvae. Because of different lifestyles, it is difficult for burial insects (aka burial beetles) and dung beetles to have any intersection - burial beetles are busy looking for dead bodies of rats or birds at this time. Like dung beetles, there is a complex set of behaviors in the unique lifestyle of the burial armor – all for the next generation.
When I was a kid I loved collecting creatures, almost all of them. Once, I saw a dead mouse in the woods outside the hut and wanted to turn it into a skeletal specimen and collect it. In order to prevent scavengers from coming to plunder my booty, I first tied the rat carcass to a nearby stake with a thin wire, and then carefully covered it with a layer of fallen leaves for further protection. I thought to myself that the industrious ants would surely be able to help me clean up the body and leave me with a perfect specimen. As a result, when I came to check a day later, I found that the rat carcass had disappeared, and there was nothing under the fallen leaves, but the wire was still there and had been going deep into the ground. My rats were buried! Upon closer inspection, I found a pair of burial armor digging in the earth, and they wanted to bury my rat deeper. Similar to the dung beetle couple mentioned earlier, this rat buried deep in the ground will also feed the next generation of buried nails.
The couple will continue to feed on the corpse while watching over the growth of the larvae, and they will even secrete antibiotics to inhibit the activity of bacteria in the corpse. In contrast, dung beetles only lay one egg in each fecal ball, then bury the dung ball and continue to look for new feces and lay new eggs. Thanks to them, the African savannah has not been inundated with herds of zebras and the droppings of countless species of antelope. The African savannah is home to more than 200 species of dung beetles, which help bury large amounts of feces and play an irreplaceable role in ecology. Surface feces (such as cow dung) inhibit plant growth and breed swarms of mosquitoes and flies, spreading parasites and diseases. In addition to burying the surface feces in the ground, these busy dung beetle moms and dads also efficiently fertilize the soil and loosen the hard soil.
The importance of dung beetles is particularly prominent in Australia. In order to develop the beef industry, Australia has introduced beef cattle, which is good for hamburger producers, but the damage to the environment is very large. After a while, Australia didn't have enough large dung beetles to deal with the excrement left by the beef cattle, and soon the pasture land was covered by a layer of stone-dry, hard cow dung. Cow dung is like a layer of cement, which further reduces the land's absorption of already scarce rainwater, inhibits the growth of pasture grass, and ultimately leads to a massive reduction in land production. It's clear that the large dung beetle is the key to being overlooked by the Australian outback.
The species diversity of the Beetle is very rich, and this abundance is not only reflected in the large number. Whether larvae or adult, dragon lice are greedy carnivores in lakes and ponds; ladybugs have become good friends with humans in the garden because they can destroy aphids; fireflies can bring us happiness with their own yellow-green light... But beyond that, there are countless other members of the insect world, such as dangerous wasps carrying highly poisonous venom and stinging needles, elegant dragonflies flying along river banks and streams, and stinking bed bugs, honey bees picking among flowers, annoying flies, and so on. Let's put the topic of beetles aside and discuss the overall situation of the insect family.
The number of insects
If you are looking for a biological phyla with a large number of species, you will find that it is still inseparable from the insect family. There are about 150,000 species of flies as dipteran insects, and about 120,000 species of butterflies and moths of Lepidoptera insects. These two orders, together with all species of Beetles of the Coleoptera order and other relatively small phyla in relatively small numbers, have found nearly 1 million species in the insect order, and this is only the current research findings of humans. There are currently about 115,000 species of ants, bees and wasps known as hymenoptera insects, but some experts have estimated that the true number of insects of this purpose alone on the earth is close to 1 million species!
The above is that some biological phyla contain a large number of species, and what is more, the number of individuals in some species is too large to count. The most emblematic example of this is the locust plague. In addition to their large numbers, locusts are also very capable of flying, and they can destroy crops and cause famine. Among the locust families, the most notorious is the desert locust, which is widely distributed between North Africa and India, so famous that even the Bible predicted its disasters. In eastern Ethiopia in February, while doing fieldwork with my students, I witnessed a swarm of locusts, and we stopped by a road in the high mountains and saw an eerie "cloud" in the valley in the distance. It was morning, and at first I thought it was the morning fog, but I thought it was strange -- the humidity of the early morning should have cleared long ago. The next day, the "cloud" (actually a swarm of locusts) swept through our camp, and the whole process took nearly an hour. The "locust cloud" was about 2,000 meters long and 500 meters wide, and I couldn't believe my eyes when I stood under the "cloud" — that was too much. Fortunately, they were all moving at full speed, with no intention of stopping and eating. A few days later, we observed the swarm of locusts flying over the highest mountain in the area, Mount Garamurata. You know, if you want to climb over this mountain, they have to fly to an altitude of 3400 meters! Some scholars have estimated that the number of locust swarms in East Africa is as many as 50 billion. At 2.7 grams per locust, this swarm weighs 115,100 tons. That's the weight of a locust! Today, through the calculation of rainfall patterns by global meteorological satellites, the outbreak of locust plagues can be predicted, and people have the ability to take measures to intervene in the reproduction of locusts.
Another large outbreak of insects, with an astonishing number, appeared only in the eastern United States. This outbreak is strictly punctual and the interval is incomparably long. Every 17 years (13 years for some southern-living species), the forests of the eastern United States are invaded by deafening noises. This noise comes from an insect called a periodic cicada. The cicada lives underground for most of its life, feeding on the sap of trees and shrub roots. Unlike fully metamorphosed insects, cyclic cicadas do not go through four stages of development, and they, like locusts, have several nymph developmental stages. In the late spring of the 17th year after the last outbreak, the nymphs of the cyclic cicada burrow out of the ground and climb up the trunks and branches. Once they reach safety, they stop and make a long slit in their backs to allow the soft adults to drill out. After a few hours of stationary movement, the adults' wings become larger and the exoskeletons begin to harden —they are ready to fly. Immediately after, the male will begin to make harsh noises, hoping to attract the opposite sex by this "singing". If you run into the forest at this time, it's quite uncomfortable (fortunately they don't bark at night)! There are three main species of cyclic cicadas, different species have a very clear geographical distribution, and each cyclic cicada also strictly follows its own time law of 17 or 13 years. Although insects such as cicadas are common in tropical and temperate regions, only a very small number of cicada species in the eastern United States exhibit such punctuality.
Unique body structure
Visually, the most striking feature of insects is the legs. Adults of all insects have six legs, which has nothing to do with the type of insect, flies, bees, locusts, ants, wasps, termites, cockroaches... All have six legs, so insects are also called hexapods. Note that we are talking about adults here. Some caterpillars have six tiny legs at the front of the body, several pairs of fat calves in the back half of the body, and some insect larvae have no legs at all (such as maggots). But the adults of all insects are extremely uniform. Some insects, such as praying mantises, have special development of their front legs in order to catch prey, but even so, the characteristics of the legs are still obvious. In addition, the legs of insects are developed in pairs, and the six legs are divided into three pairs, which gives them a relatively wide range of activities. In addition, at the end of each pair of legs, there is a claw-like structure that helps them grasp, which allows the insect to pose differently and move more flexibly. At the same time, the six contact points also allow them to stay firmly on the contact surface.
Another obvious feature of insects is that the body can be divided into three sections: head, chest and abdomen, in fact, the Latin word "Insectum" of the word "insect" is originally meaning "section". The head of the insect is located at the front of the body and has the main sensory organs (antennae, eyes) and feeding organs. Different insects also have different mouthparts, some with large jaws like pincers, and some mouthparts act like straws, which can be used for piercing and sucking. Differences in mouthparts make insects' food sources unusually widespread. The second segment of the insect body is the thorax, which is the solid middle part of the insect body, with legs and wings, and the muscles responsible for flight and movement are also distributed here. The last section of the insect's body is the abdomen. The abdomen contains most of the digestive, respiratory and reproductive organs. All three sections are wrapped in a hard carapace that provides hardness and protection for the insect's body. But what is the most important reason for insect success in the competition for survival?
The Carboniferous dragonflies could grow to about 1 meter, which was very large.
A major evolution – flight
Being able to fly is perhaps the most important feature of insects. The fossil record shows that insects were the first animals to fly into the sky. 300 million years ago, the Carboniferous era left the shadow of giant dragonflies flying on the sky, and today, almost all the flourishing insect species can fly. Insect wings are not specialized legs, and it is still unclear how the ancestors of insects evolved two pairs of wings. However, it is these two pairs of wings that grow together with the legs and feet on the chest, but are completely separated from the legs and feet, which give the insects the ability to fly.
A further evolution than mere flight is the ability to fold wings and attach them to their bodies, which allows insects to be perfectly hidden in a safe tiny corner. The two ancient ancestors of insects—ephemera and dragonfly—did not have this ability, so they could not hide in small, cramped spaces. In fact, possessing the ability to fly marks the full maturity of insects. However, after they can fly, their wings can no longer be replaced or regrown, and once injured, they will be wounded for life. Whether it is an incomplete metamorphic insect (such as locusts, cicadas, bed bugs, etc.) that gradually develops from nymphs into adults, or a completely metamorphosed insect (such as beetles, flies, wasps, etc.), the ability to fly marks the end of the development of the insect body.
Have you ever hit a fly? It's not easy to hit a fly unless you have a fly shoot. The fly's sensory organs are unusually sensitive, and it can sense changes in the air pressure around you as your hand approaches, and as soon as it is perceived, it escapes. In general, the biggest feature of dipteran insects like flies is that they have only one pair of wings. At the back of the wings , the fly has a pair of short , slender , rod-like balance rods. The balance bars vibrate as they fly, helping them maintain balance and control their direction. Worse, some of the world's most obnoxious creatures belong to dipterans, including mosquitoes, stinging flies, and several other flying parasites.
It can be said that the advantages of flight and the four-stage life process are concentrated in the nasty mosquito fly. Imagine a female mosquito flying thousands of miles in search of blood to help it lay eggs. It then lays eggs in a muddy source of water, which in turn hatch into aquatic larvae. Unlike lazy maggots, these larvae prey on their own. After pupalization, these pupae will surface so that the adult mosquitoes can fly directly to find a mate, as well as suck blood (if it is a female mosquito), and finally these mosquitoes will find another source of water and continue the cycle of life. However, there are some flies whose survival strategies are even more complicated!
Once, I went to Tortuguero National Park in Costa Rica to collect specimens, where the climate was humid and stuffy, and I was bitten several times by mosquitoes because I forgot to bring insect repellent. I didn't care too much, thinking that malaria was not prevalent and that mosquito-stinged packets would subside in a few hours – not really! Two weeks after I returned to Chicago, the three mosquito packs on my body were not only still itchy, but they were getting bigger! These bags looked like growing tumors, extremely scary, so I decided to see a dermatologist, but I didn't expect to go to the hospital, and the doctor couldn't see the cause, so I had to arrange for a biopsy a week later. During that time, I painfully imagined every day before going to bed that cancer was worsening under my skin. And one of these three worsening "tumors" was on my right thigh, one on my left arm, and one on my forehead. One day, before I could do my biopsy, I was lying in bed and suddenly heard a "click" and "click" sound coming from the "tumor" on my forehead!
This "tumor" can actually make a sound! Although I don't know about cancer, at least I know that malignant tumors don't make a sound. I remembered a similar case in Ethiopia and realized that three skin flies were parasitizing under my skin. Early the next morning, I excitedly called the doctor, who quickly arranged for me to remove the surgery. When I arrived at the hospital, doctors, nurses, and a large group of medical students greeted me, after all, few people in Chicago needed to take the skin fly maggots out of their bodies. My surgery became a "show" I would never want to see, so I lay on the operating table and stared quietly at the ceiling. The operation began, and when the second maggot was removed, a tall surgeon in a surgical gown suddenly rushed in. He watched carefully as the surgeon removed the last maggot and blurted out, "It's disgusting." ”
Not disgusting at all! It's amazing. My body formed new tissue around these maggots, so they were confined to my skin. As maggots grow larger and larger, they push and squeeze the surrounding tissue, creating a sound. Until now I have a small pit in my forehead, and this is what is caused by the maggots pushing and squeezing the surrounding tissue. But the most amazing thing is that I infected skin flies through mosquito bites! It seems that skin flies are not good at finding mammalian hosts, but mosquitoes are very good at it, so all a female skin fly needs to do is find a female mosquito, and then lay the eggs on the mosquito's leg and let the mosquito help find the thermostatic mammal. This sounds more like a science fiction plot than a real animal behavior, but it happens to be strong evidence that insects form a unique means of survival – they can even combine flight with other complex behaviors! A zoologist working at the Field Museum of Natural History once recalled that decades ago he had collected a jaguar specimen from southern Mexico and accidentally found countless maggots of skin flies while peeling off the specimen.
Many wasps are also flying parasites. Go to the tomato stalks at the end of the summer, and you'll surely see the larvae of the tomato moth covered with small white cocoons. The appearance of these cocoons is due to the larvae of a small parasitic wasp that has already consumed the poor caterpillar to the fullest. In the process, natural selection led wasps to come up with a very clever tactic — their larvae would eat the non-lethal parts of the host's body first, and then digest the host's deadly organs. In fact, the world's smallest insects are parasitic bees, they will implant eggs in the eggs of other insects, hatching larvae will feed directly on the eggs in other people's eggs, and finally, a new small parasitic bee will "hatch" from other people's eggs.
Taken together, insects have become one of nature's most successful forms of life, relying on their ability to fly, varying lifestyles, and relatively small size. Leafminers, including the larvae of certain small moths and flies, feed only on the epidermis of the leaves. The world's smallest beetle, the Beetles of the Family Tamarindidae, live in the decaying leaf litter of the forest, only a millimeter long, and lay only one egg at a time, and no beetle can be smaller than them!
Returning to the topic of the huge number of beetles, it is necessary for me to talk about the research done by entomologist Terry Owen in Panama. Owen sprayed insecticide spray on the same tree (Luehea seemannii) and then used canvas spread under the tree to collect fallen insects. He tried to use this method to estimate the number of insects on the canopy of the same tree. Owen sprayed 19 trees and collected countless small insect specimens, including 8,000 beetles containing about 1,200 species — and that's just one tree. Panama is home to over 2,000 trees! If these species of beetles lived only on the canopy of one or two trees, you could imagine the number of beetles throughout Panama (later, Owen estimated that there were still a large number of beetle species in the world that remained undiscovered, but he may have exaggerated it). There is no doubt that if the beetles could not fly, they would not be able to live on the canopy. However, despite the diversity and sheer number of insects, these "hex-legged animals" never seem to grow large and are clumsy.
Why haven't insects gotten bigger and smarter?
Each broad category of animals has a strictly unchanging body structure – insects have 6 legs, spiders have 8 legs, and crabs have 10 legs. We humans have similar laws. All vertebrates, whether frogs, toads, reptiles, birds, mammals, have four legs. A pair of bird's forelimbs are specialized into wings, and our forelimbs are specialized into arms, but this distinction is only a small modification under the same blueprint. Our ancestors evolved from the early quadruped amphibians, and the fact that we are quadrupeds will never change. It seems that once a new form of body structure is established, such as "the body of an insect is divided into three sections", the animals belonging to this structure can no longer be changed. But losing some kind of body structure is a different matter. The process of degeneration occurs frequently, and many insect wings have degenerated. While the dolphin specialized its forelimbs into fins, the snake threw away all its limbs. However, even with the presence of degradation, the basic body structure of each animal type will not change. That's why we can tell the difference between insects, spiders and crabs at a glance. However, that being said, there are still huge differences in body shape between mammals, small shrews (even less than a large beetle called "giant flower diving golden turtle"), elephants, whales... Why isn't the world of insects like this?
There is more than one reason. First, if insects want to get bigger, they have to shed their hard exoskeletons first. Adults of locusts (orthoptera) and bed bugs (hemiptera) undergo several molting processes before they mature. These insects do not have a four-stage life cycle of beetles and flies, etc., they develop from eggs to small nymphs, and then slowly grow up and undergo at least four molting processes before they can grow into sexually mature adults. In fact, the nymphs of locusts look the same as wingless adults. In contrast, fully metamorphic insects with a four-stage life cycle complete their full growth at the larval stage, followed by the main morphological transformation at the pupal stage. Take, for example, the larvae of the tomato moth that erodes tomato plants, which, after growing, become pupae and then feather into moths, which have a curly "tongue" that can reach up to 10 centimeters when extended. The tomato moth uses this "tongue" to suck nectar deep inside the flowers, flapping its wings as frequently as hummingbirds. From the hard chewing mouthparts of the larvae to the slender "tongue" of the adult, the same insect has two very different ways of survival.
Pupae create the possibility of experiencing different ways of living for fully metamorphosed insects, but all insects are still limited after they mature. Whether it is locusts, beetles, wasps, butterflies, mature insects can not continue to grow, because they can neither continue to molt nor regenerate their wings. Large insects do exist, such as the giant flower-diving golden turtle in the African rainforest and some spade beetles in Europe, and their adults are large because the larvae are also large. But since the larvae are largely defenseless against foreign enemies, they need to hide in an absolutely safe environment. The larvae of these large beetles generally live deep in the decaying wood, are very difficult to find, and they take 4 to 8 years to develop and pupate. This process is too long, or it is better to keep the body petite.
There is another reason for this. A large, active animal is like a small, bigger, more powerful car that needs more fuel to drive, and the car's fuel fuel has to burn more efficiently. This means that the animal needs to inhale more oxygen for breathing consumption. Among terrestrial animals, birds have the strongest lungs. In birds, there is a complete pathway for oxygen to enter the lungs and then flow out. This mechanism is necessary for the consumption of continuous rapid flight. And that's the main problem with insects — they don't have organs that function as lungs. Insects suck in air through the breathing holes around the body, and oxygen is absorbed by the blood before being transported throughout the body. This breathing pattern is not at all the same as the human use of alveoli to increase the surface area of oxygen-absorbing organs, thereby prompting oxygen to be absorbed by the circulatory system, let alone the diaphragm that helps us inhale and exhale gas. Paleontologists speculate that giant insects appeared during the Carboniferous period because for a short time there was oxygen content in the air at 30 percent, up from 21 percent today. When the oxygen level of the air becomes lower, the giant insects disappear. In addition, the activity of brain tissue requires a lot of oxygen, so the limited oxygen absorption further restricts the development of small insect brains.
In summary, the limitation of exoskeletons coupled with insufficient oxygen absorption makes insects doomed to be "small and exquisite".
The above facts raise an even bigger question: Why are insects limited by their anatomy? Similarly, why can't land vertebrates grow two hands in the last 300 million years of evolution? Imagine scratching your back when you're running out of hands and legs! It seems that all the animal phyla with a large number of members are stuck by this stereotypical body structure. Thanks to the latest genetic research, we finally understand why each animal is limited to a specific body structure. Research has shown how a small, undifferentiated cell undergoes a series of rigorous activities to evolve into a larger, higher animal body. A small ball of cells, the original embryo, is formed by the fertilized egg after undergoing several simple cell divisions, but from the protodermal stage, the developmental instructions of the animal's body are triggered, directing the embryo to develop in a complex direction. Some of the cells in the embryo will form a hollowed sphere in the middle, and then the "wall" of the sphere will continue to be depressed, and finally the entire sphere will have two cellular levels. Further enlargement and elongation will clearly show the head and tail. This is the first step in the embryonic development of all animals, as are worms, beetles and vertebrates. Different developmental directives not only form the diversity of species to a certain extent, but also the diversity of cells and tissues in higher animals. However, once a species' instructions have begun to be executed, it is impossible to change it.
Further understanding of animal development
The late ecologist Robert MacArthur suggested dividing biologists into two categories: engineers who explored how things worked, and historians who cared about how things developed to be what they are today. And animal diversity, whether it's billions of beetles or hundreds of species of cells, can also be examined using these two taxonomic approaches. The first is to explore how things work. Nowadays, there are too many beetles living on the earth, too many complex tissue structures in a small fly, too many complex reaction processes in each organism...... Conversely, we can ask the "historian" question: Why are there so many Beetles on Earth? How did the evolutionary directives that created so many species of plants and animals come about?
Human beings develop from simple embryos into babies, and butterflies feather out of pupae, these are all magical changes in nature. Both variants are strides from simple to complex structures, and both are driven by similar genetic instructions, although the variants of different species are unique. This trajectory has also brought the beetle family to billions of members. But even though they are numerous, we should be amazed by them. Because from them, we see the real miracles around us.
Today, the rapid development of genetic research has led us to realize that fruit flies, mice, and humans are actually using similar genes to build their own bodies. The mystery of morphological evolution is slowly being unraveled, and the similarity of the genes of various animals is no longer the product of mysterious powers. And this makes it clear that from ancient times to the present, nature has used the same set of tools to create countless creatures that allow us to share the earth.
Why are there no insects in the sea?
Earth is the only blue-and-white planet in the solar system because our planet is rich in water, and more than three-quarters of the Earth's surface is covered with water or ice. From the distant outer space, you can see the white clouds on the surface due to the rise of a large number of water droplets, and the white clouds slowly fluttering on the surface of the blue planet. Our homeland has a lot of water, and it's where life was first born — life originated in the ocean. Take a walk to the beach and count the species of creatures that have been washed onto the beach by the sea. You don't have to count species, just count how many doors there are. The phylum is a very high classification level in the animal kingdom, fish, crabs, starfish, jellyfish, sea shells, and countless species of animals that look like worms belong to different phylums, all the phylums of the animal kingdom have representatives living in the sea, but in so many "representative" figures, where have the insects gone?
Insects belong to a very large phylum of the animal kingdom, the arthropod phylum. The animals of this gate have pairs of legs and feet, including crabs, lobsters, horseshoe crabs, spiders, scorpions, centipedes, horses, and of course insects. There are many arthropods living in the sea, including several spiders and a very small number of insects, but not horses and scorpions. The larvae of aquatic beetles and mosquitoes live in water most of the time, but they live in fresh water. Why do almost all insects inhabit terrestrial or terrestrial aquatic ecosystems?
Insects are terrestrial animals, and even if they did evolve from water, they would have to be fresh water. Judging by the oldest surviving insect species, they appear to have originated in lakes and streams – far from the sea. The species richness and complexity of terrestrial habitats allow insects to multiply in abundance, a number that no other organism can match. A simple explanation for insects not going out to sea is that there are plenty of predators waiting for them beneath the waves.
Similarly, vertebrates first landed from streams and estuaries, rather than from the sea. Throughout the evolutionary history of life, mammals evolved from reptiles, and since then, only a small percentage of mammals have chosen to live in water, such as otters, beavers, hippos in freshwater, whales, dolphins, seals, and sea lions in the seawater. But these aquatic mammals, no matter how long they can dive underwater, have to surface on time and breathe fresh air. They abandoned the habits of their terrestrial ancestors, but never learned the ability to breathe underwater.
Next, let's leave the animal kingdom and see another class of land creatures. Such creatures also have a large number of family members, flowering plants, which botanists also call an angiosperms.
Another large family – angiosperms
Angiosperms, or rather, flowering plants, are not only diverse, but also vary in size. If you catch a beetle in a large jar, you may catch 1,000 and not be able to fill the jar, but the flowering plants are the opposite, they are usually very large. The smallest flowering plant is duckweed (of the duckweed family), which varies from the size of the letter "O" you see today, to 2-5 centimeters. There are only more than 30 species of duckweed family, which is at the bottom of the list of flowering plant sizes. At the other end of the leaderboard, you can see eucalyptus trees that are 97 meters tall, baobab trees with trunks as wide as trucks, and sea coconut trees with light leaves that can grow up to 11 meters long. Simply put, flowering plants are the most diverse family of large creatures that have ever lived on Earth. From duckweed to giant trees, flowering plants are major members of terrestrial ecosystems. Fish also vary widely in size, with the largest whale shark weighing 40 tonnes, but only about 30,000 species of fish. The mammal family has the largest animal on the earth, the blue whale, which can reach 30 meters in length and weighs far more than 100 tons, but there are only about 5500 species of mammals in existence. However, there are more than 260,000 known flowering plant species, and about 1,000 new species are discovered each year, and at this rate, more than 300,000 species are just around the corner (the constant discovery of new species makes the figure of 300,000 seem to become the "ultimate goal" for the number of angiosperm species. Many new species of angiosperms are found in "biodiversity hotspots", which are discussed in detail in Chapters IV and V).
Considering these three characteristics, which are large in size, variety, and autotrophic through photosynthesis, you will find that flowering plants are the biggest winners in the biological world. The angiosperm phylum mainly includes grasses (10,550 species), legumes (19,500 species), orchids (22,500 species) and Asteraceae (23,600 species). However, it should be noted that a large number of species does not mean that they are common in habitats. Orchids are relatively rare to see in most plant communities and are less conspicuous in a variety of natural landscapes. In montane cloud forests, orchids often grow as epiphytes attached to trunks and branches, but even so, they are rare. Grasses, however, are different, and they often live in thousands of places, often dominating the eye of various natural landscapes. That's why many parts of the planet, including temperate, tropical and alpine, are called "grasslands."
With large numbers, diverse body shapes, and complex structures, flowering plants dominate most ecosystems today. In addition to their own exquisite structure, flowering plants are also a source of nutrition for other animals. With the exception of a few, the vast majority of flowering plants are green and photosynthetic, so they are at the bottom of the food chain. It is because of these flowering plants (and of course other kinds of green plants) that solar energy can be converted into nutrients for our use. Over the past 100 million years, as the number of flowering plants has increased, other organisms have only begun to have the ability to expand their own numbers. A 1998 study clearly showed that more beetles feed on flowering plants than on other food sources.
Conifers are not flowering plants, but they often dominate habitats with cooler climates and more pronounced seasonal variations. Common conifers are pine, fir, sequoia, juniper, pine and araucaria. However, although these conifers are regular visitors to many forests, they are only about 1,000 species in total. And, although the cold north and many alpine jungles are covered with conifers, such plants really only have a form of "tree", and only the seedlings of these conifers are in the lower layer. What's more, conifers secrete a variety of chemicals to protect themselves, which makes conifers an excellent building material. Because few animals feed on conifers, not only are there no animals in the subsperm of the taiga, but other vegetation species are rare. In contrast, flowering plants put more energy into growing, did not pay much attention to self-defense, and used idioms to describe them as "dying young", but they can thus provide energy for other nutrient-rich vegetation. In addition to flowering plants and conifers, species-rich and more important land plants include ferns. There are nearly 12,000 close relatives of ferns and ferns (such as stone pine and horsetail), of which almost none can grow tall, but most of them are common in the lower layers of humid rainforests, and some are important members of the epiphyte family of rainforest subspermity. In addition, because ferns, mosses, and the sperm produced by their close relatives need to swim in the water, these plants can only grow in evergreen forests or seasonal rainforests.
In summary, flowering plants are not only the most numerous, the most nutritious, but also the most beautifully colored land plants. We have noticed that there are far more species of plants and animals on land than in the oceans, but this conclusion may not apply to the biological kingdom, especially the smallest life form, bacteria. Whether it is the number of individuals, the number of species, the diversity of physiological and biochemical processes, or the ability to withstand extreme environments, bacteria on Earth occupy a well-deserved top spot.