Pre-schools, swimming lakes and public pools have closed across Germany in recent weeks as city workers try to contain an infestation of caterpillars in oak trees.

Around 70 percent of some 250 oak trees in Cologne house these caterpillars, the larval form of the oak processionary moth, according to the Rheinische Post newspaper. Other cities in North Rhine-Westphalia and western Bavaria have fenced off trees and shut down parts of parks and school grounds to protect citizens from these creepy crawlers.

"It is as bad ever," Wolfgang Auler of a pest control company based in the town of Velbert told the Rheinische Post.

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In its larval state, the oak processionary moth has long hairs, or setae, which contain thaumetopoein, an irritating protein that can cause rashes, swelling and breathing issues. The setae are especially dangerous for those with allergies or asthma problems and can be deadly in some cases.

"This is already the case with healthy people," said Peter Schütz, the spokesperson for the Environment Ministry in North Rhine-Westphalia. "The risks are significantly greater with seniors, kids and people with allergies."

The United Kingdom has experienced a similar infestation from this caterpillar species, with the British Forestry Commission issuing a warning at the end of April.

Warnings have cautioned Germans against these caterpillars as they spread through oak trees

Crawlers of climate change

The caterpillar infestation has only affected some regions, according to Schütz. "There are fewer oak processionary caterpillars in the cool mountain regions than in the warm flatlands."

But the insects have spread to regions of Bavaria in recent years after previously not existing in the region.

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"With climate change, the oak processionary caterpillars have spread from Lower Franconia to southern Bavaria," Hubert Messmer, the head of the forestry department in Bavaria's Department of Food, Agriculture and Forestry, told the Augsburg Allgemeine newspaper.

Messmer also said the ecosystem in the Swabian region in southern Germany has yet to adjust to this invasive species. "Predators such as birds, beetles or bugs must first get used to them."

The nests of the caterpillars in oak trees are between 20-30 meters (66-98 feet) off the ground. Exterminators have to search the branches with binoculars and use a special vacuum to remove the caterpillar nests.

This particular species of caterpillar has been limited just to oak trees. The caterpillars usually emerge at the beginning of May, but turn into moths between July and September.

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