Why were insects bigger in past?

The leading theory is that ancient bugs got big because they benefited from a surplus of oxygen in Earth’s atmosphere. But a new study suggests it’s possible to get too much of a good thing: Young insects had to grow larger to avoid oxygen poisoning.

Does higher oxygen levels make animals bigger?

Higher oxygen levels means animals can grow larger and still maintain the supply of oxygen to their muscles.

How do insects increase in size?

As the insect grows, tracheal tubes get longer to reach central tissue, and get wider or more numerous to meet the additional oxygen demands of a larger body. Insects can limit oxygen flow by closing their spiracles.

What factors limit the size of insects?

The tracheae interface with the atmosphere through paired, valved openings called spiracles. This system may limit the body size of insects because the net rate of oxygen mass transport by diffusion is inversely proportional to the distance of diffusion.

Do insects get bigger in high oxygen environments?

One way to investigate this is by raising insects in high oxygen environments to see if they get bigger, but this approach hasn’t yielded many consistent results. Insects are an incredibly diverse group of animals, and each group will encounter vastly different habitats.

Why are some flies bigger than others?

Flies reared at high oxygen concentrations are bigger, but not so big that the size isn’t explained by pre-existing genetic factors. They also return to normal size after being returned to normal oxygen conditions. Image credit: Klok et. al, 2009

Why did bugs get so big in the past?

So while oxygen availability certainly played a central role, I’m not sure it was the only reason bugs got big back in the day. There’s a lot of reasons animals reach immense sizes, and being large has its advantages. Ladybird beetles, for example, tend to be big enough to attack their prey. This is something seen in moths, as well.

How do insects breathe?

Very briefly, insects breathe through a series of tubes called trachea. These trachea deliver oxygen directly to the tissues of insects, and how much the insects invest in these trachea depends on how much oxygen is available to the beetle’s tissues.