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Native species that may be mistaken for oak processionary moth

Home research Native species that may be mistaken for oak processionary moth

OPM with photo credit


This page lists the caterpillars which are most often mistaken for oak processionary moth (OPM) through our advisory service Tree Alert. All seven of the species described on this page are straightforward to identify, but if after checking this page you are still unsure then please submit an enquiry through Tree Alert.


Please click on the caterpillar of interest (at the bottom of the page) to access its species-specific page with more information.

Oak processionary moth feeds only on oak and produces large nests on oak trunks and large branches from May onwards. Hairy caterpillars which are not on oak or are not associated with a silk nest are almost certainly not OPM. In very rare circumstances however, caterpillars which have fallen from the nest may be found in isolation, in which case they can be identified as OPM by their long white hairs on a dark, un-patterned body.

All caterpillars with hairs have the potential to be allergenic and direct handling is best avoided. However only oak processionary moth and brown-tail caterpillars produce enough allergens to be considered potentially harmful.


Look-alike species

Some caterpillars feed socially in communal nests built from silk webbing on oak trees which can look similar to those produced by OPM. The two most commonly reported are the lackey moth (Malacosoma neustria) and brown-tail moth (Euproctis chrysorrhoea), which are often encountered during spring and early summer. However, both species will feed on a wide range of other trees as well as oak.

Small ermine moths (Yponomeuta spp.) also produce large quantities of conspicuous silk webbing on a variety of host trees and shrubs, although they do not occur on oak. They rarely form discrete nests, but instead a diffuse sheeting across the host plant.

Less frequent, are larvae of the small eggar moth (Eriogaster lanestris), which also produces a silk nest. This species was formerly common in hedgerows, but it has become scarce and rather localised. It does not feed on oak.

Although they do not build any form of nest, the hairy larvae of the buff-tip moth (Phalera bucephala), vapourer moth (Orgyia antiqua) and young gypsy moth (Lymantria dispar) are often seen in groups, sometimes in quite large clusters. All three species will feed on oak, but the colourful and brightly marked caterpillars are easy to distinguish from OPM

Quick Facts

This table can be used to identify suspect OPM caterpillars. The important characters for identification are in bold. Sizes represent the usual range for caterpillars when encountered, they may be smaller than this in some situations.


Hosts and time of year



Oak processionary moth

Only on oak, caterpillars build nests May-July, but nests may be found year-round.

Small to large rounded nest on the trunk or branch of the host tree.

Dull, grey-brown to black with pale underside. Hairs are extremely long and pale. Small, 20-30mm.

Lackey moth

Wide variety of broadleaved trees and shrubs, including oak, in April-June.

Nest spun between host twigs in a tent shape.

Brightly coloured with blue, orange and white stripes. Short ginger hairs. 40-55mm.


Wide variety of broadleaved trees and shrubs, including oak. Caterpillars active March-May, next generation in very late summer-Autumn.

Nest spun between host twigs in a tent shape.

Two orange warts toward the tail and white ‘dashed’ markings on sides. Hairs white to orange mid-length. 30-45mm.

Gypsy moth

Wide variety of broadleaved trees and shrubs, including oak. April-July.

No nest built, but usually found in groups. 20-50mm long egg mass may be mistaken for nest.

Young caterpillars black, but bright blue and orange warts on grey background on mature caterpillar. 10-50mm.

Small ermine

Broadleaved shrubs and small trees, not found on oak. April-June.

Sheet nest across large areas of the host.

Pale cream to yellow usually with black spots, but variable. Hairless. 15-20mm.

Small eggar

Generally hawthorn and blackthorn, rare on other broadleaves. Not found on oak, April-July.

Nest spun between host twigs in a tent shape.

Dark with orange-red tufts of hair with white outlines on the body. 30-50mm.


Broadleaved trees including oak. July-October.

No nest built but social when young.

Dark but with thin yellow stripes and bands, including a V on the head. Short pale hairs. 30-60mm.


Wide variety of trees and shrubs, rarely oak. May-September.

No nest, not social.

Colourful but variable. Four pale tufts of hair toward the head and two pairs of forward or side-facing black tufts distinctive. 20-40mm.


Please click on the caterpillar of interest to access its species-specific page with more information.


lacky_moth_larvae_thumb.jpgbrown_tail_moth_larvae_thumb.jpgbird_cherry_ermine_moth_larvae_thumb.jpgGypsy moth caterpillar thumb

Lackey moth            Brown-tail moth      Small ermine moth    Gypsy moth




Small eggar moth      Buff-tip moth          Vapourer moth 


Photo of Lackey moth larvae © Steve Bennett

Photo of Small Eggar moth larvae © Jennifer Wiggins

Photo of Vapourer moth larvae © Ian Kimber