Butterflies flourishing in hot weather

You've probably heard about it by now: insects are dying off. And not just a few of them here and there; many species are in dramatic decline, and in many regions around the world.

So it may come as pleasant surprise to see more butterflies around this summer. Turns out the heat wave that has large parts of Europe sweating and complaining about record temperatures is actually a good thing for many butterfly species!

Ecologist Paul Ashton from the University of Edge Hill in the United Kingdom explained that many butterflies' flight period is limited by cold weather and rain in summer.

The insects were off to a good start because last winter was cold in many northwestern European countries. Although it may seem counterintuitive, harsh winters are actually good for butterflies, because the cold kills off fungal diseases that threaten their larvae.

So with a cold winter behind us and a hot, dry summer that is still playing out in Europe now, there are more butterflies, which are able to fly around longer and feed on lots of nectar. Great, right?

Well, don't get too excited. Sadly, due to the extreme heat, "there could be problems down the line" for the tiny beauties, Ashton said.

Read more: Rethinking evolution: Butterflies came first, flowers came second

Some mountain species like the marsh fritillary are better at adapting to colder weather — they live at higher altitudes, and their larvae can even survive freezing temperatures.

Many mountain species like it are dark-colored, so they can stay warm by absorbing heat from the sun. But with the high temperatures this summer, they overheat quickly.

There's also a limit to how much higher they can go to escape the heat — because the mountain doesn't go any higher, or at some point they won't find plants to feed on anymore.

Even species that don't live at higher altitudes will struggle once egg-laying season rolls around, Ashton said. While many plants butterflies usually lay their eggs in have died from the heat, fewer plants means fewer eggs, fewer caterpillars — and eventually, fewer butterflies.

So next summer, you might not see that many butterflies around anymore.