Demystifying science | Insects face the threat of winter

Every week, our journalist answers scientific questions from readers.

Most insects secrete an antifreeze molecule, but a small minority migrate south.

When we examine how insects spend the winter, we must distinguish the different stages of their existence, notes Philipp Unterweger, a German biologist who founded an insect protection organization.

“They are first eggs, then larvae, and only then insects in the form we know,” underlines Mr. Unterweger in a telephone interview. Beetles, for example, can spend up to six years as larvae and only live a few weeks or months as adult insects. The type of antifreeze and strategy for survival is very different in the three stages of an insect’s existence. »

To protect themselves from threats, which range from insect-eating woodpeckers to fungi, insects usually hide in the ground or in damaged wood.

Urban fields

Mr. Unterweger founded an organization that ensures that insects are protected by preserving the places they choose to hibernate. “The biomass of insects has decreased by 30% over the past 30 years in Central Europe. In Germany, it’s 80%. When there are fewer insects, particularly large, more vulnerable insects, there are fewer insectivorous birds. Protecting places where insects can survive the winter is crucial to countering this decline. »

Studies published by Mr. Unterweger have shown in particular that stopping mowing urban green spaces in the month or two preceding the cold season allows us to preserve long grass and flowers where eggs and larvae can shelter.

He also suggests avoiding cutting a portion of forage fields. “In Germany, forage fields are very diverse, with lots of flowers, they are ideal places for larvae and eggs to spend the winter. »

What proportion of insects spend the winter as adults? “We don’t know, any more than we know in what proportion they migrate south,” replies Mr. Unterweger. There are tens of thousands of insect species in every region of the world, but often only their final form is known, as a specimen pinned in a glass cage in a natural history museum. Virtually nothing is known about most insect species. »

The same lack of studies does not establish whether insects that live in warm regions year-round have different behaviors, or life cycles, from those that must survive cold winters.

“In some areas, instead of having to survive the cold season, insects have to survive the dry season,” notes Unterweger.

Do you have a scientific question? Write to us