Processionary Caterpillars
From Contact 65:
PROCESSIONARY CATERPILLARS
This is a subject of recurring fascination, every year when the “nests” appear in the pine trees. The question I am asked most is “are they butterflies or moths?” Many thanks to Gareth White of RAF Akrotiri for allowing us to reprint his recent article from the Lion which pretty comprehensively tells us everything we need to know – including that it is a moth!
An impressed Sheila Cole relates that when they called the Council about an infestation of processionary caterpillars a team was quickly despatched to spray them.
"There are two main types of caterpillar that can inhabit our gardens at this time of the year; The March Caterpillars and the Processionary Caterpillar.
The March Caterpillars pose no hazard to residents. However, the Processionary Caterpillar has tiny hairs that cover it which contain an irritant toxin and therefore pose a hazard to residents who may come into contact with them.
How Can We Tell The Difference?
Nests of both species resemble a white silky cotton wool like texture. March Caterpillars nest on the ground, unlike the hazardous Processionary Caterpillars which nest high up in Pine trees.
During the next 4 – 6 weeks (dependent upon the weather but possibly in March) the mature caterpillars will emerge from the nest, try and seek shelter and pupate into the pine processionary moth. (Thaumetopoea pityocampa)
Life Cycle Behaviour
It is before pupation that the presence of the larvae (Caterpillars) is most apparent. Their procession in search of a suitable site for pupation brings them more into contact with people and animals. A procession first forms when a large larvae gather into a tight ball, which later flattens out into a disc of larvae rotating around a single caterpillar. This central figure is often the leader of the procession when it forms a line. Then each larva in the procession maintains contact with the others as they move to a suitable area to pupate, often up surrounding pine trees.
In Their Defence
The defensive mechanism by which the larvae may cause ‘nettle rash’ consists of hairs containing a poison fluid. The exact nature of the poison is not known. The projection comes off readily and can easily penetrate the skin, when the top of the spine beaks off releasing the poison. The poison spines are situated on ‘buttons’ or ‘mirrors’, positioned in pairs on each segment of the larva. Normally covered by fold of skin the mirrors become exposed if the caterpillar is alarmed.
The degree of injury depends on the amount of poison injected and the sensitivity of the individual. The symptoms usually begin with a local burning stinging and the affected area becomes red and elevated and whitish, with a redder border extending across by as much as 2.5cm.
Occasionally these weals may develop over the entire body and further complications may cause muscle cramps, and intense headaches. Medical assistance should be obtained immediately upon coming into contact with the poison".
Gareth White.