Principle species colonised.
The most critical clue is the host. OPM lives and feeds almost exclusively on oak trees. If you see caterpillars or nests on other tree species (like blackthorn, hawthorn, or fruit trees), they are likely a different, often harmless, species like the Lackey or Ermine moth.
Identification.
April through July is when caterpillars are most active. They travel in lengthy, nose-to-tail lines, as their name implies (processions). These frequently take the appearance of an arrowhead and might be single-file or many caterpillars wide.
They are coloured with a dark head and a grey body. Older larvae have whiter stripes on either side of a noticeable dark stripe in the centre. They have long, white hair all over them.
Type of symptoms.
Among the symptoms are:
- In late spring and early summer, caterpillars march from nose to tail down the trunk.
- Sometimes the procession is shaped like an arrow, with rows of caterpillars trailing after a single leader.
- Nests on oak tree trunks and larger branches.
- The characteristic white silken webbing used to make them fades to a light brown hue.
The threat to host.
The oak processionary moth only produces one generation annually. The caterpillars finally develop the annoying hairs after going through several instars after hatching in the spring. As they grow, the caterpillars move lower down the tree, removing its leaves along the way, making it weaker and more vulnerable.
They withdraw into nests and pupate during the summer. In order to mate, the adult moths only survive for four days after emerging in late summer. The cycle is restarted when the female deposits her fertilised eggs high in the tree canopy.
Impact / Effect / Significance
Originally found in London, the oak processionary moth’s range is growing every year into the nearby areas of Kent, Essex, Hertfordshire, Hampshire, and Berkshire. Despite efforts at regulatory control, it is projected to be growing at a rate of 6 km annually. This pace could rise due to climate change.
