Scientists have figured out why insects can not reach gigantic sizes

(ORDO NEWS) — One of the best things about evolution is that it didn’t lead to tank-sized cockroaches. Insects tend to stay relatively small, but why is that, and how big can an insect be?

In ancient times, many insects and arthropods were larger. The largest insect of all time was Meganeuropsis Permiana, a dragonfly that lived during the late Permian, about 275 million years ago.

The wingspan of these dragonflies was about 75 centimeters, and the weight was more than 450 grams. Insects such as satin moths (Attacus atlas), which have a wingspan of 27 centimeters, are no match for their distant relatives.

Why are insects getting smaller?

One theory is that insect exoskeletons are not strong enough to support large bodies, and as insects grew, their exoskeletons must have become thicker than possible.

In favor of this theory is the fact that arthropods in the sea do become larger. At sea, their exoskeletons don’t have to support the weight of their bodies the same way they would on land.

However, as Arizona State University entomologist Dr. John Harrison explained, the data doesn’t really support this theory.

Larger arthropods (on land) have no thicker exoskeletons than smaller arthropods, which is to be expected if the theory is correct.

Another theory is that the way insects breathe prevents them from becoming truly massive.

“So, insects breathe in a completely different way than humans,” said the entomologist.

“They have a series of holes on the sides of their bodies, and then oxygen enters through those holes and enters as a gas into the air-filled tubes.

And these tubes branch out, like a branching tree, and become very small, down to a micron in size.

So it’s really tiny and can get close to every cell.”

Larger insects may not be able to get enough oxygen through these tubes to sustain life. What supports this theory is that insects were more than millions of years ago.

“This idea has received recent support from geologists, who have shown that the late Paleozoic atmospheric oxygen content was significantly higher than today,” Harrison explained.

“Now it has 21 percent oxygen, and in the late Paleozoic, we believe it was about 32 percent oxygen.

And this coincides with when we had much larger insects than we do today.

And that, in a way, supports the idea that oxygen delivery is what makes insects small, and that higher atmospheric oxygen may allow them to get bigger.”

So, all you have to do to get cow-sized insects is pump oxygen into the atmosphere, create a stressful environment, and wait for evolution to do its thing.

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