This butterfly, which also lives in the Netherlands, may be adapting its appearance due to climate change

Scientists have long wondered why brown sand-eyes often have varying amounts of spots on their wings. New research now suggests it has everything to do with temperature.

The research shows that just a few extra degrees can have a major effect. This is during the period when caterpillars are still in the cocoon to eventually become a butterfly. The research shows that butterflies that are exposed to a temperature of 11 degrees during that period have an average of six dots, while butterflies that are exposed to a temperature of 15 degrees in the same life phase only have three dots. The research therefore suggests that climate change may lead to the disappearance of dots.

Custom camouflage
Scientist Richard ffrench-Constant contributed to the research. He said: “Our results suggest that butterflies adapt their camouflage based on the environment. To give an example, in this case it is likely that brown sand eyes with fewer spots are more difficult to see on dry, brown grass. This brown grass is more common during warm weather.” The research has been published in the journal Ecology and Evolution.

Catching butterflies
For the research, the British scientists collected butterflies daily from a field near Cornwall during the flying season. They then compared their contemporary observations with what they see in butterflies in historical collections. This shows that female butterflies in particular are sensitive to losing spots on the back of their hind wings (see box). “We did not see this effect as strongly in male butterflies,” says ffrench-Constant. “This is probably because males need their spots to attract females.”

Front and back
Brown sand-eyes have two pairs of wings. There are always two large dots on the inside of the front pair. There are several small dots on the back of the rear pair. Ffrench-Constant explains: “The large spots on the forewings are probably intended to deter hunting animals. The spots on the hindwings are much smaller and especially good for camouflage. It is mainly these small dots that can disappear.”

The scientist therefore expects that future brown sand eyes will have fewer and fewer dots as it gets warmer. Ffrench-Constant concludes: “This is an unexpected consequence of climate change. We often expect animals to move north slowly. So in this case we see a species that is changing its appearance.”