Recently, eighteen Alvalade, Lisbon, schoolchildren were hospitalised with skin rashes following contact with processionary caterpillar hairs. Fortunately none of the cases were serious. The reports lauded the city’s “competent services” for swiftly discovering and removing nests of the dreaded caterpillar from the school’s play area.
Pine processionary caterpillars do not tickle my fancy.
The moth larvae are harmful to pine and cedar trees, of concern where forestry is important to a country’s economy. After forest fires, they are Portugal’s second biggest cause of coniferous tree destruction. That aside, touching or breathing in the hairs of a fully developed caterpillar causes health issues in humans and animals.
Dogs get necrosis of the tongue when they sniff and lick them. If the dog vomits, foams at the mouth, has swollen lips, or shows paw or snout irritation, urgent veterinary attention is necessary to avoid possible fatalities. Humans get urticaria, an itchy rash of round red wheals accompanied by swelling and, following contact with infected fingers, eye irritation.
At summer’s end, adult female moths lay their eggs near the tops of pine trees. Covered in scales, the eggs mimic pine shoots. After hatching, the larvae create silken tent like nests to keep warm. These look like big balls of cotton candy in the tree. To avoid predators, the caterpillars are night feeders. During the ensuing winter, a developing caterpillar will devour enormous quantities of foliage, hence the risk to the tree.
From February to the beginning of April, depending on the weather, the caterpillars leave the nests in the procession for which the species is known. A dry and sunny winter will speed up their development and they will come down from their nests earlier. That is why, this year, they have already made their appearance in Lisbon, Monsanto and some areas of Malveira da Serra.
A caterpillar has eight sacks on its back, covered by some 100 000 microscopic barbed ‘hairs’ that are released as it moves. For protection from birds, the hairs are toxic and cause dermatological reactions when in contact with the skin of humans and other mammals. That is what the trouble is all about.
This time of the year, I keep a wary eye on Guinness my dog, whenever we are anywhere near pine trees.