General Question

Ltryptophan's avatar

Did very tiny animals, particularly insects, evolve to be smaller or did they start smaller and got larger?

Asked by Ltryptophan (11810points) 2 months ago from iPhone

Fleas, tiny gnats, spring tails, mites, lice, are all examples of small animals.

But, are they typically shrinking in size over evolutionary time, or getting larger. I don’t expect all of them to necessarily have the same evolutionary history, but I am interested in the pressures that might have shrunk them to such small scale.

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4 Answers

ragingloli's avatar

Insects used to be a lot bigger in prehistoric times, because oxygen content was much higher than today, so atmospheric composition puts a limit on their size.
This also holds true for other animals, but for insects especially, since almost all of them have a passive respiratory system, which relies on passive diffusion of air into the body, which makes it harder to supply oxygen to all parts of the body with larger body sizes.

Blackwater_Park's avatar

@ragingloli Beat me to it. If you look at insect fossils they were often huge. It is a direct result of the oxygen levels in our atmosphere. Insects basically absorb oxygen and this is why dish soap and water is so effective in killing them. There are also some limitations due to the ratio of gravity and density of our atmosphere on flying insects.

Ltryptophan's avatar

So, any little mite that fits on this little dot . <— probably had a big arthropod ancestor, right?

HP's avatar

Yep. A dinosaur today would require oxygen tanks. So much for Jurassic Park, and dragonflies with 2 foot wingspans.

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