Why are insects bigger in tropical areas?

12 February 2019

BEETLE

Beetle on flower

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Question

How come all the biggest insects tend to be in tropical regions?

Answer

We received this question from James in Amsterdam for our insect expert, Eleanor Drinkwater from York University. It was then over to vet Stuart Eves who is all too familiar with animals, great and small.

Eleanor - Well, this is one of the things I love most about the tropics is the incredible sizes of just spiders that would blow your mind, and beautiful beetles. It is really down to two really simple things: for something which is an invertebrate to get big it tend to need two things, one of which is warmth helps, it's better if it's a bit warmer, and then also having constant access to food. So somewhere like the UK you know you have this problem about winter.

And so you know everything kind of stops over winter, whereas in the tropics you kind of have this amazing opportunity for things to be able to develop all the year round, which is why you end up getting the opportunity for some of these amazing species. The really interesting thing though, is that - so that’s on the species level, on the individual level, microclimate is really really important. So for example their conditions which a particular beetle might have to grow up on one side of a garden might be completely different to a beetle that lives on the other side of the garden because one side has shade and one side has sunlight which means that on the individual level it's the microclimate that's the really important thing. So big species grow in the tropics but just because it's in the tropics it doesn't necessarily mean that it'll reach its full potential.

Chris - But humans... Because we don't feed someone properly they don't grow very much. Stuart?

Stuart - Yeah, only really that it does compare with what's happened in development of domestic dogs, where as we've domesticated them one of the things we think's happened is that because they wouldn't have maybe got as much food as they could have done in the wild, it's led to them becoming smaller. And of course from our point of view, that was great because no one wants a wolf when you could have a slightly smaller cuter looking wolf. So actually this kind of not necessarily getting the nutrition that you would normally need has actually, I say benefited us, but it's part of the domestication process. So it kind of rings true with that.

Chris - So what happened to a pug then?

Stuart - We happened to pugs I'm afraid..

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