Fewer poisonous caterpillars so far this year; Thunderstorms could make things worse

Oak processionary caterpillars
Oak processionary caterpillarsPhoto: Luc hoogenstein/Wikimedia Commons

The number of poisonous caterpillars to have hatched so far this year appears to be markedly lower than this time last year, according to the findings of a group of researchers who published their results in NatureToday on Saturday. The results will likely come as relief to doctors after large numbers of the infamous oak processionary caterpillars hatched in the summer of 2019, leading to public health concerns as well as predictions that the situation may worsen in 2020.

According to the findings, the number of oak trees on which the caterpillars were found stood at 30 percent on average since the first caterpillars began hatching in early April. In comparison to last year, where 55 percent of oaks were found to have had the caterpillars over the same period, the findings represent a substantial decrease.

However, according to the researchers, the number of caterpillars still remains high, and weather conditions could potentially lead to their numbers spiking further. "Due to the expected heavy thunderstorms, nests, caterpillars or hairs can blow from the trees, with additional nuisance as a result," researcher Silvia Hellingman warned.

Oak processionary caterpillars, which metamorphosize into a species of moth, are regarded as pests due to the damage they can inflict on oak trees by feeding on their leaves. In addition, the caterpillars are known to cause health concerns in humans, where their bristles act as an irritant which can trigger asthma, rashes, conjunctivitis, and, in extreme cases, even anaphylactic shock.

Last summer, a particularly bad season of oak processionaries saw between 60 thousand and 100 thousand Netherlands residents run into some form of irritation as a result of the caterpillar hairs, with pets such as dogs and cats also being affected in a similar way.

Many residents have tried to spray the caterpillar colonies with bacteria in an attempt to kill them off. However, the researchers advise against the practice, saying that it is more sensible to leave the caterpillars alone.

"We strongly advise against [spraying], particularly because the oak processionary caterpillars are no longer very affected to the bacteria, while other butterfly species are affected, causing negative effects on biodiversity," explained Hellingman.