What is the Largest Insect that Ever Lived?

Scientists found through fossil records that before the dinosaurs, there were huge species on the earth. They were giant arthropods of the Carboniferous period 300 million years ago, including oversized maggot insects and scorpions; spider plants the size of spiders; and 5 feet Long millipede, etc. The two most characteristic insects are the giant-veined dragonfly Meganeura and the ancient tapeworm. The wingspan of the giant dragonfly can reach 2 1/2 feet (approximately 1 meter), the size of an eagle, and the largest insect on earth. These species flourished 300 million years ago. At that time, most of the land was in the tropics and the plants were flourishing (they were buried underground to form coal, which was therefore called the Carboniferous Period). But after about 50 million years, from the middle to late Permian period, these giant species died out.

Giant ancient insect

The mystery of prehistoric giant animal extinction has been the focus of scientists' research. The latest research says that the emergence and decline of giant flying insects millions of years ago may be related to the amount of oxygen that their larvae can breathe in the water.

The Carboniferous Period was not only the era of giant insects, but also the era of insects opening up the sky. To this day, insects are still the only arthropods with flying capabilities. Some scientists think that the insects mentioned at the beginning of this article may be capable of flying, but they have not been confirmed by fossils. The more generally recognized ability to fly is considered to have appeared 320 million years ago. Regardless of the aforementioned "maybe capable of flying" ancient insects with no wings found, the earliest known dragonfly is currently flying into the sky. ^[3]

For a long time, scientists have speculated that perhaps the changes in the oxygen content of the atmosphere played a key role in their rise and fall. Palaeontologists have begun to investigate whether the rise and fall of these ancient dragonflies, cockroaches, and other supertype insects the size of today's eagles is related to the high oxygen content.

Dr. David Bilton, of the University of Plymouth's School of Oceanography and Engineering, who participated in the study, said: "In prehistoric times, higher levels of oxygen by affecting their larvae may have contributed to the evolution of giant insects, many It may not be accidental that extinct behemoths have to go through the aquatic larva stage. "The research results were published in the Public Science Library, and Wilton-Wilbok, author of Bilton and his co-author, noted in the article Aquatic insect larvae are more sensitive to fluctuations in oxygen levels than terrestrial adults that breathe in the air.

Although scientists have previously suggested a link between oxygen levels and giant insects, no one has provided conclusive evidence of how they are linked. The study focused on stone flies, which said that aquatic larvae such as dragonflies, stone flies, and pupae obtain oxygen directly from water, and the water body has much less oxygen than air. And larvae are much less efficient at getting oxygen from water than adults that breathe in the air. Scientists say that they may be more sensitive to changes in the available oxygen, which may be particularly important for aquatic larvae, which determines the upper limit of insect body growth.

Giant insects are a major feature of sci-fi stories involving distant pasts. Michael Crichton's novel Jurassic, featuring giant dragonflies as a feature.

Giant ancient insect

"Park", produced a movie giant with box office income of millions of dollars. Scientists believe that records show that this giant insect with a wingspan of 75 cm lived in the Carboniferous period about 354 to 290 million years ago. Wilburk said: "So far, attempts to understand giant insects that lived in the past have mainly been achieved by observing (fossil) terrestrial adults. Our work has shown that the problem of prehistoric giant disease through larvae may be It helps us better understand how oxygen limits insect body size. "

In ancient times, the oxygen content of the earth's atmosphere far exceeded today's standards, and paleontologists learned that fossil specimens in ancient times were generally larger than modern ones. Why were ancient insects so huge? Scientists speculate that this may be related to the atmospheric oxygen content at that time, and insects "respired" through the stomata system on their bodies. The stomata are connected to the trachea, and more and more layers of smaller and smaller stomata are attached from top to bottom, thereby sending oxygen to the whole body. At today's oxygen levels, the total length of the stomata system has reached its limit; beyond this limit, the oxygen level becomes insufficient. Therefore, this structure can effectively determine the size of the insect. The atmospheric pressure in the Carboniferous era was indeed higher than it is today.

In high-oxygen environments, large insects have an evolutionary advantage, they can get more oxygen. Studies of invertebrates in the ocean have also found that in colder and more oxygen-rich waters, there is also a larger biological volume there. Studies of fruit flies have found that some fruit flies increase in size in a high-oxygen environment, and some do not. However, in the environment with high oxygen content and high air pressure, the fruit flies tested lived to the fifth generation, and their body size increased by 20%. This is because higher atmospheric pressure causes more oxygen to enter the insect. ^[4]

Square high oxygen concentration created ancient giant insects

The oxygen concentration in the Carboniferous Earth's atmosphere is as high as 35%. Not long ago, a paleoclimate study published by Yale University biologist Robert Berner and others confirmed this speculation.

Researchers pointed out in the report that the concentration of oxygen in the Earth's atmosphere during the Carboniferous period was as high as 35%, which is much higher than the current 21%. Many arthropods absorb oxygen directly through miniature trachea throughout their bodies, rather than indirectly through blood, so high oxygen levels can encourage insects to evolve toward larger heads.

These knowledge comes from the study of the flight mechanism of ancient dragonflies. Scientists have long believed that such a huge dragonfly can only glide and cannot fly. "It's clear that they can fly," said aviation engineer Roy Beckmaier. One of the key conditions is that their wings can swing, bend, and twist. Modern dragonflies rise and advance by bending and twisting their wings.

Fossil data show that the ancient dragonfly has a fold structure similar to modern dragonfly on its wings. Modern dragonfly can twist the outer wings, while ancient dragonfly can slowly twist all wings, so they may not fly too fast. But it can still fly.

But for such huge insects, even slow flight can generate a lot of heat due to muscle movement. Therefore, the ancient dragonfly must have a way to discharge its own heat, otherwise they will be roasted to death by their own body temperature. This was first pointed out by entomologist Michael May of Rutgers University in the United States.

Scientists have found that modern dragonflies, like other insects, have a body fluid called hemolymph (the blood of invertebrates) that circulates throughout their bodies. When they are too hot, they will increase the flow of hemolymph in the abdomen. Their abdomen is long and thin, and they can dissipate excess heat through convection. It's like the car's cooling system removes heat from the engine.

Although no direct evidence has been found, May thinks it is likely that ancient dragonflies also had similar mechanisms that allowed them to fly for long periods without overheating. No direct evidence was found because fossils usually only retain bone material. ^[4]

Inverse body size may not necessarily be related to oxygen content

Insects adapt to changes in oxygen concentration through various skills.

Although the analysis by Bernard et al. Is wonderful, some scientists are still skeptical, and some even come to the opposite conclusion.

Giant ancient insect

To investigate the root cause of changes in insect body size, University of Arizona insect researcher Jon Harrison and his colleagues fed locusts, rice worms, fruit flies, and other insects in different oxygen levels and measured their size Measure to answer whether the high-oxygen atmosphere of ancient Earth is related to the evolution of ancient giant insects.

Harrison originally thought that larger insects would find it more difficult to survive in low-oxygen environments, but this was not the case. For example, small locusts cannot survive in low-oxygen environments, especially those with an oxygen concentration of less than 15%, and adult locusts can survive in an environment with 2% oxygen.

Harrison said at the United States Geological Association and the Canadian Geological Joint Conference that in preliminary experiments, they placed some modern insects without breathing apparatus like their ancestors in an oxygen-rich environment, and found that higher oxygen levels were not necessary. Larger individuals are produced, and lower oxygen levels do not necessarily result in smaller individuals.

Harrison explained that insects use a variety of skills to adapt to changes in oxygen concentration. These skills include increasing stomata and increasing the amount of fresh air entering the body. Among these insects, some are better at increasing the amount of fresh air inhaled, while others are better at expanding the size of the stomata. It is for these reasons that they have different answers to the questions they are studying.

Whether the size of the insect is related to the pressure.

Harrison said, "I want to ask why modern insects are so small?" In the past, researchers guessed that compared with 21% of today's atmospheric oxygen content, the oxygen content of the atmosphere during the Carboniferous period reached 35%. In this environment, large insects are more likely to be produced. Harrison's research found that body size and oxygen content may not necessarily be related.

So, is the insect size related to the pressure?

At the same time, John Vanden Brooks, a paleontology graduate student at Yale University, performed the same experiment on crocodiles. Try to find out whether the environment with an oxygen content of up to 30% during the Permian period left any clue in the bones of the animals that lived in it. It was found that crocodile living in a certain high oxygen content environment is larger. When the oxygen content exceeds 27% or 28%, the change is not so obvious. Brooks also plans to feed rainbow crests in a different oxygen environment in the next experiment and observe how it changes over several generations.

In addition, through research on fruit flies, scientists have found that some fruit flies increase in size in a high-oxygen environment, and some do not. However, in the environment with high oxygen content and high air pressure, the fruit flies tested lived to the fifth generation, and their body size increased by 20%. Is the pressure also related to the size of the insects?

The inconsistency of these experimental results must lead to questions about previous conjectures: Did oxygen really make ancient giant insects? Did the demise of giant insects in ancient times really be caused by a decrease in atmospheric oxygen concentration? The answer to these questions seems to require more sufficient evidence. ^[4]