The State Plant Protection Service (VAAD) has received a report of a possible outbreak of the browntail moth (Euproctis chrysorrhoea) at a farmstead in Eleja parish, Jelgava municipality. On inspecting the site, a VAAD inspector confirmed that it was indeed the browntail moth.
An outbreak of the browntail moth was first observed in Zemgale in 2021, and in 2022 and 2024 the moth was found to have spread to new sites in the same Zemgale region.
THE DANGER:
The pest strips the leaves of many broadleaf trees and also poses a threat to human health.
The cuticle of the moth's caterpillars is covered in dense hairs. The caterpillars use these hairs to defend themselves, shedding them. The hairs are very fine and sharp and contain a toxin that causes inflammation of the skin and also of the eyes, while in people prone to asthma it can cause serious breathing difficulties. These hairs can persist in the environment for several years. They are very light, and the wind can lift them back into the air. The rash they cause may appear immediately after contact with the caterpillar hairs, or several hours later. The rash can last from a few hours to several weeks. Hairs are also present in the webs the caterpillars build, in the cocoons they spin before pupating (about the size of a fist), and in the skins they shed when moulting. The hairs of the adult moths are not allergenic. Medical treatment usually involves relieving the unpleasant symptoms (itching). The toxic hairs pose the greatest risk from the beginning of May to the end of July.
In addition to the problems associated with human health, an outbreak of the browntail moth lasting several years can also cause trees to die back.
Description of the pest:
The browntail moth needs plenty of light and warmth, so it is usually found in sunny places such as thinned stands, forest edges, avenues, orchards and similar locations. The caterpillars are polyphagous and can therefore be found on broadleaf trees of many species — among others, they can damage oaks, aspens, limes, elms, hawthorns, fruit trees (pears, plums, cherries and so on) and various other broadleaf trees.
The browntail moth has one generation a year. The moths lay their eggs in July. The eggs are laid in clusters on the undersides of leaves and covered with hairs from the female's body. The young caterpillars hatch from these eggs in August. The caterpillars feed in groups on tree leaves and in autumn build webs into which both twigs and leaves are woven. Several hundred caterpillars may gather in a single web, and they overwinter in these "nests". The webs are usually small — roughly the size of a fist. The webbed "nests" are concentrated in the upper part of the tree crown. The caterpillars resume feeding in April as the leaves come out. Once they have overwintered, the caterpillars disperse and feed individually. The fast-growing caterpillars can leave spreading oaks completely stripped of leaves. However, although trees defoliated in this way look doomed, they are able to recover the following year. On the whole it should be said that such trees die only in very rare cases — most often when they have been subjected to several other adverse factors at the same time, not just the effects of the browntail moth. When cooler weather sets in, the caterpillars return to their nests. In June the caterpillars pupate either in groups or singly. Before pupating, the caterpillars disperse in search of a place to pupate. At this stage of development, the caterpillars may wander into people's homes in large numbers. In late June and early July, white moths with a brown rear section of the body emerge. The moths are attracted to light. These are mostly males. The females hide in the foliage of the host plant.
The caterpillars can easily be spread by cars parked under infested trees. It is therefore important not to park vehicles beneath such trees. Mass outbreaks usually end when pathogenic fungi spread through the pest population. When working in places where the browntail moth has multiplied, it is advisable to wear safety goggles, a respirator, gloves and close-fitting, dry clothing. If outdoor work is planned in dry weather, it is advisable to water the yard so that the toxic hairs are not lifted back into the air but instead "stick" to the ground. To get rid of caterpillars that have taken over dwellings, the best method is a vacuum cleaner with a water filter, adding a little soap to the water. If an outbreak has only just begun, cutting off the webbed "nests" in winter and early spring, while the caterpillars have not yet left them, is highly effective.
WHAT TO DO
- If you suspect the browntail moth is present, it is important not to expose small children and people prone to asthma to the risk of an allergic reaction.
- The only effective course of action on finding the browntail moth is to cut off the branches with the caterpillars on them and burn them. To avoid a possible allergic reaction caused by the caterpillar hairs, rubber gloves must be worn when doing this, and a respirator and safety goggles should also be used.
- Before doing garden work or mowing the lawn, it is advisable to water the ground to avoid possible contact with browntail moth hairs.
To establish the extent of the outbreak, people in Latvia, and especially those living in the Zemgale region, are asked to report sightings of the pest to the State Plant Protection Service by email at zinas@vaad.gov.lv, sending photographs of the caterpillars.