Poisonous caterpillar makes early return thanks to warm weather

The first oak processionary caterpillars crawled from their eggs one week earlier than usual on April 1 as temperatures rose, the Knowledge Center for Oak Processionary Caterpillars reports. The hairs the caterpillars later grow cause health problems among Netherlands residents every year.

Initially, the caterpillars were expected to hatch on April 11 which was later changed to April 8. In the end, the caterpillars hatched even earlier on Thursday, due to temperatures in parts of the country climbing up to 25 degrees Celsius. Only in 2014 did the caterpillars hatch earlier on March 30. Some larva will emerge delayed due to a drop in temperature in the coming days.

Sinking temperatures will not be a problem for the frost resistant newly-hatched caterpillars, the research center stated. In their first stage, the larvae eat the buds of oaks and can survive a long time with a limited amount of food. Once oak leaves emerge in around one month, they move on the second larva stage.

Bare branches, nonetheless, make the caterpillars easy prey for birds, ants and spiders. Some municipalities are using birdhouses to attract birds like the tit to get rid of the caterpillars before they mature and develop their irritating hairs. 

When the adult tits rear their young they catch as many as 555 caterpillars every day. To encourage this, the Lions Club gave free birdhouses to children in Noordoostpolder and asked them to decorate them and hang them around the town. The City of Amersfoort gave 750 birdhouses to its residents for use at home as one way to fight off the caterpillars during the spring.

The oak processionary caterpillars are expected to develop their stinging hairs in the upcoming weeks. Every year thousands of people sustain eye injuries from the minuscule hairs. If the hairs of the caterpillar penetrate the eye, they can cause serious vision damage.