A global warming flap

Differences in butterfly and moth breeding patterns are linked to a changing climate

Florian Altermatt likes to chase butterflies. This ecologist — a scientist who studies how creatures interact with their environment — who works at the University of California, Davis. And he thinks that butterflies might have something to tell us about the effects of global warming. In a new study, he and other researchers found a big change in the reproduction pattern of butterflies and moths in Central Europe.

Two butterfly species, the small heath (left) and common blue (right)
Two butterfly species, the small heath (left) and common blue (right), are among those in Central Europe that have become more likely in the last 30 years to have an extra generation in the same year. Since 1980, average temperatures there have also risen. F. Altermatt
Over the last 30 years, the average temperature in Central Europe has gone up by about 1.5 degrees Celsius. During that same time, 44 species of moths and butterflies in an area around Basel, Switzerland, have added an extra generation to their numbers during some years, Altermatt found. That means that if butterflies of one of these species used to reproduce once a year, they sometimes now reproduced twice. And if they used to reproduce twice, they sometimes now reproduce three times.

These extra generations didn’t show up in this location before 1980.

The temperature increase, 1.5 degrees, may not seem like much, but it’s about the difference between the body temperature of a healthy person and someone with a low-grade fever. Altermatt suspects that in Central Europe, that extra degree and a half is changing the internal clocks of many butterflies and moths. Because the climate has warmed, their breeding season begins earlier. And this could give the insects more time to mate.

Altermatt notes that the increase in temperature also speeds up the development of the insects. That means they’re ready to reproduce earlier in their lives.

This was no small study: His team watched butterflies and moths outdoors and also looked at historical records for more than 1,100 types of the creatures. Among these, 263 species are known to produce one or two extra generations in the location studied. But not always. This happened only when the temperatures heated up. Since 1980, Altermatt found, most of those species have started adding generations more often.

These added insects might mix things up in the ecosystem of Central Europe, says Patrick Tobin. He’s an ecologist with the U.S. Forest Service in Morgantown, W.Va. An extra generation of insects provides more food to the animals that feed on them. Those predators, in turn, might start to increase their numbers. And that could make life tougher on the species those predators eat, Tobin told Science News. On the other hand, if an endangered insect species was affected, an extra generation each year might give it a better chance of recovering.

Altermatt also does research in evolution, which is the study of how species, or groups of the same creature, change over time. Every time an insect — or animal, plant or other organism — reproduces, the offspring might be slightly different from its parent. These differences could give the offspring a better chance of survival in the world. In this case, Altermatt thinks the additional butterfly generations may speed up evolution. That, too, might give them a better chance of survival in the face of climate change.

Scientists who study the effects of climate change like to look at patterns such as insect populations because they are easy to track — and easy to connect to a warming world. And by studying such visible effects of climate change, scientists might be able to better predict the changes ahead for other populations — like humans.

Stephen Ornes lives in Nashville, Tenn., and his family has two rabbits, six chickens and a cat. He has written for Science News for Students since 2008 on topics including lightning, feral pigs, big bubbles and space junk.

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