Researchers at the Oak Processional Caterpillars Knowledge Center have discovered that oak processionary caterpillars can sit in nests underground for ten months, only to suddenly crawl out en masse in June.

This makes the processionary caterpillar's control a lot more complicated, reports

Nature Today

.

In recent years, oaks were found in various places in the Netherlands that were unexpectedly full of oak processionaries.

The leaves of these trees were less eaten than expected with the large number of bugs.

These places had also already been sprayed with pesticides.

Based on research, researchers from the Oak Processionary Caterpillar Knowledge Center have established that this can be explained by soil nests.

The caterpillars can sit in the ground for ten months without moving to their next stage of development.

When the caterpillars come out, the caterpillars grow to the stage where they develop stinging hairs.

It is then too late for spraying.

"It therefore means that as a tree owner you still have to keep a close eye on the sprayed locations later in the season and be aware that at risk locations you still have sufficient capacity to suck away oak processionary caterpillars," says

Nature Today

.

The researchers also have positive news.

Parasitic wasps and parasitic flies, natural enemies of the oak processionary caterpillar, can also go underground.

"Stimulating natural enemies is therefore also an interesting option for soil nest control."

Contact with the hairs of the oak processionary caterpillar causes irritation to the skin, respiratory tract and eyes in humans.

The most violent physical reaction is life-threatening anaphylactic shock.