Lighter-colored butterflies and dragonflies do better in warmer areas of Europe, a finding that could have implicated for global warming; darker insects could face a competitive disadvantage, finds a study recently published in Nature Communications.

Light-colored insects dominate the warmer south of Europe and darker insects dominate the cooler north. For dragonflies, the insect assemblage in Europe has on average gotten lighter during the last decades, which the authors attribute to climate change.

Insects, like lizards and snakes absorb energy from the sun to become mobile. The darker the color they have, the more sunlight they can exploit. Therefore it makes sense to see darker insects in cooler climates. However, the researchers were surprised to find such a distinguished color pattern between the northern and southern species, since the surface colors also serve many other purposes such as camouflage. This underlines the importance of heat regulation in insects.

 "When studying biodiversity, we lack general rules about why certain species occur where they do. With this research we've been able to show that butterfly and dragonfly species across Europe are distributed according to their ability to regulate heat through their color variation," explains leading author Dirk Zeuss from Philipps-University Marburg in Germany. 

"For two of the major groups of insects, we have now demonstrated a direct link between climate, insect color and habitat preference," says Carsten Rahbek, Director of the Center for Macroecology, Evolution and Climate at the University of Copenhagen and professor at Imperial College London. The study used digital image analysis of 473 different species of butterflies and dragonflies together with information on their habitat.

They also say that darker insects will shift their distribution and possibly retreat from certain areas or on a smaller scale, find more shady conditions. Such responses have implications for conservation strategies.

Closer to an explanation

The past two decades scientists have observed that several Mediterranean dragonfly species, such as the Southern Migrant Hawker (Aeshna affinis), the Scarlet Darter (Crocothemis erythraea) and the Dainty Damselfly (Coenagrion scitulum), have expanded their northern range and immigrated to places Germany.

Similarly, Mediterranean butterfly species like the Southern Small White (Pieris mannii) have dispersed to Germany during the last ten years and are still continuing their northward shift.

"Until now we could only watch the massive changes in the insect fauna during the last 20 years. Now we have an idea of what could be a strong cause of the changes," says Stefan Brunzel, co-author from Philipps-University Marburg.