Many of you may have read about strange caterpillar (moth larvae) invasions occuring in European and African cities. This blog has mentioned invasions of dangerous oak processionary caterpillars in the past, but these are not the only caterpillars that sometimes invade urban areas. As it turns out, several different species of moth larvae sometimes descend upon populated cities, and not all of them are dangerous to humans. A fairly recent caterpillar invasion in the Netherlands caused residents to flee the city in fright, according to a news report released by the popular website “Nerdist”. However, the invading caterpillars are not dangerous to humans, but their relationship with trees is a different story.

Back in the summer of 2009, an invasion of ermine caterpillars struck the Major Dutch city of Rotterdam. The army of caterpillars numbered in the tens of thousands, and likely even more. The ermine caterpillar gravitates toward trees, most notably spindle trees, but they cover just about every object that protrudes from the ground with their silk webbing, including street signs, bridges and even cars. Most people probably assume that spiders produce the greatest amount of silk for web-construction. However, this is not the case, as spiders cannot match the speed with which ermine caterpillars produce silk.

If you were in Rotterdam during May of 2009, the web-spinning prowess demonstrated by this caterpillar would probably have caused you to go running for the hills in fright too. Ermine caterpillars feed on tree leaves for a period of six to eight weeks during the early summer season. In order to avoid predators during this feeding stage, these caterpillars, completely cover trees in white shrouds of silk. After this period, they begin their metamorphoses into butterflies. However, these caterpillars must travel from tree to tree, and they must find a proper location to undergo metamorphosis without making themselves vulnerable to predators. Without their protective coat of silk, these caterpillars are completely defenseless. This means that these caterpillars must cover every object within their path while foraging. This protective behavior results in entire regions becoming covered with enormous white webs, and this scene has been described as resembling thick snow coverings. Ermine caterpillars even create a silk shroud over grass petals as they travel across open areas of land. Not long ago, a similar invasion occured in Cambridge, England. The resulting coats of silk that covered a portion of the city reminded the residents of ghosts. The dumbfounded residents then nicknamed the exceptionally odd scene the “walk of ghosts”. According to experts, these formerly uncommon invasions will only become more common as climate change intensifies.

Have you ever witnessed the ghostly aftermath of an ermine caterpillar invasion?