Insects are the most diverse and numerous animals on earth. They range from microscopically small wasps to stick insects that are over a foot long, and they live on every continent (including Antarctica!) We don’t know exactly why there are so many different insects, but we’ve described about a million species, and scientists believe there are probably millions more. 

Insects are typically active at warmer temperatures and inactive when it’s cooler. You might have noticed this, when insects pretty much disappear in the winter. Part of this is because insects are generally considered ectotherms, or animals that can’t keep themselves at a constant internal temperature (as opposed to endotherms, like us and other mammals). Both humans and insects can be found from the Arctic to the Antarctic, but while humans can adjust to a huge range of ambient temperatures, individual species of insects can usually only tolerate the specific conditions they evolved for.  

These limitations on insect life are especially important to understand in light of climate change – if most insects can only tolerate very specific conditions, their survival is imminently threatened by those conditions changing or disappearing.  

Maybe no group of insects represents this better than the Grylloblattodea, or “ice crawlers.” Grylloblattids have an even narrower range of liveable temperatures than most insects, and because of that, they’re trapped in their rapidly shrinking and highly threatened habitats. The question of grylloblattid extinction seems more like one of “when” than “if.” 

But even insects that are well-adjusted to extreme heat may be threatened. There’s an upper limit to how hot animals can get, because eventually proteins (one of the macromolecules that support life, like lipids and carbohydrates) will denature (or lose their shape so they can’t function – this is why meat cooks when exposed to high heat). And the insects that already live at very high temperatures – like the Sahara silver ant – may not be able to survive at even higher temperatures. 

Parasites like lice are also threatened, because many of their hosts are. Lice can’t keep living on seals – or birds, or even other insects – if there aren’t any left. 

Human action – through anthropogenic climate change and habitat destruction – is the most significant threat to insect diversity. And as much as you may hate getting bitten by mosquitoes in the summer or finding a cockroach in your house, insects are critical for life on earth. A world without insects would be totally unrecognizable – not only harder to live in, but much less interesting. 

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