British forestry officials warn parts of London of an invasion of caterpillars whose long, white hairs can cause allergic reactions in humans, including skin and eye irritation, respiratory problems and even anaphylactic shock.
Caterpillars of the oak processionary moth were discovered that emerged from the eggs in mid-April, according to the Forestry Commission monitoring forests in England and Scotland. Caterpillar hair, which can be released as a defense mechanism or carried by the wind, contains taumetopoein, an irritating protein, the commission said. Those who are allergic can get sick.
British officials have issued similar warnings in recent years as they struggled to stop the insect from spreading. This year, the forestry administration began treating trees in a "control zone" around the infected area with biopesticides that use viruses or bacteria that cause the most damage to the pest. The treatment is expected to continue until the end of May or the beginning of June, with the prospect of affecting trees at more than 600 sites, said.
"We advise people not to pick up the caterpillar or pick up the nest," said a spokeswoman for the UK Department of the Environment, Food and Rural Affairs, adding that there were no reports of serious illnesses because of contact with the caterpillar. Robert Glatter, an emergency physician at Manhattan's Lenox Hill Hospital, said that the speed of response after contact is typically slower than that of a bee sting.
He said that each caterpillar has more than 62,000 poisonous hairs, Those who remain after the release can remain active for up to five years. "Here comes the true toxicity of the caterpillar," he said, adding, "Know the wise – it's best to observe their beauty from afar."  The caterpillars build "unmistakable white, silky webbing nests on the trunks and branches of oak trees" in early summer and also leave behind "white silk traces," according to Forstbeamte.  Mr. Dombroskie said mature caterpillars have bodies that are dark above and paler on the sides, completely covered with thick hair and "with a few pale orange spots".
The caterpillars not only feed and feed on humans and animals, but oak leaves leave the trees bare and susceptible to pests, floods and droughts.
The oak processionary moth is native to southern Europe, but is held in check by natural predators such as beetles, parasitic wasps, flies and pathogens, said Mr. Dombroskie. Its name comes from its almost exclusively on oaks and its movement in what forestry officials called "nose-to-tail processions" in late spring and early summer.
"When they travel from tree to tree, they go in a procession, and they are in a straight line," said Mr. Dombroskie. "None of our caterpillars in North America does that."
They were accidentally brought to Britain in 2005 when live oak plants imported from Europe contained their eggs. The moth is limited in southern England, mainly in London and some neighboring counties, but could flourish across the country as it spreads, British officials said
. Dombroskie said the moth is not yet in the United States, but is on a watch list of potentially invasive insects. He's in a task force with New York State and federal government agricultural officials overseeing traps in ports across the country.
The caterpillar would most likely come to the United States through an infested nursery school. It would thrive in the southern United States and could even be problematic for New York City where Central Park has 2800 oaks.
In general, he said, "The loss of oak forests would be quite dramatic, it's a valuable tree and valuable shade tree."
Instead of worrying, Mr. Dombroskie said the public should be on guard.
"People in the United States are not here, so do not worry, but we should continue to be vigilant," he said. "We have agricultural inspectors in circulation, but half of the new things in the US are found by the public sending them in."