Species of the day: Brown-tail Moth

By James Duncan

Learning and Engagement Officer

The Brown-tail (Euproctis chrysorrhoea) is one of around 2500 moth species in the order of Lepidoptera found in Britain. It's one of the so-called 'macro' moths, comprising approximately 900 species which as a whole are larger, and hence easier to study. It should be noted that there is, however, size overlap between the 'macro' and 'micro' moths and the split between the two is largely one of convenience, not science. The Brown-tail is one of a small number of moths whose larvae live and feed in communal colonies, highly distinctive as the community takes the form of a silken tent - other moth species that do this include the Lackey (Malacosoma neustria) and Small Eggar (Eriogaster lanestris). They will typically be found browsing members of the Rosaceae family, including Hawthorn, Blackthorn and Bramble and may be found in significant numbers in parks, gardens and amongst coastal scrub. Historically this moth was restricted to the south-east of England but has gradually expanded its range to spread across southern and eastern England and in recent years, further inland. 

In late summer the female Brown-tail will lay her eggs in a series of batches, covering them with red-brown hairs from her abdomen for additional protection - this hairy egg-mass may look quite bizarre if seen in isolation. The moth itself is rather attractive, with a silky snow-white body and wings and if disturbed may well raise the distinctive abdomen (that gives them their name) into view. It isn't long after the larvae emerge that they'll soon spin their silken cocoon, overwintering until the days grow longer and the sun shines with greater intensity. Every so often Brown-tail populations may really take off, resulting in localised 'outbreaks.' This isn't a new phenomena and is something that's been happening for hundreds of years, though increasing numbers are perhaps a symptom of our warming climate. As with many moth species, the caterpillars have a defensive strategy to help avoid predation - their hairy nature. This doesn't work for every predator and amongst some birds and parasitic insects, one of its key predators is the Cuckoo. The rapidly declining Cuckoo is a true specialist of 'hairy caterpillars', occupying its own ecological niche. 

Unfortunately for the Brown-tail its reputation precedes it, for its barbed urticating hairs may prove more problematic for some of us than they do for the Cuckoo. The word 'urtica' is a word shared by the Common Nettle (Urtica dioica) and translates from Latin as a 'sting' or 'burn.' Indeed, the sensation created by the tiny hairs may be remarkably similar to a Nettle sting and as a result the caterpillars should not be handled, particularly as the hairs detach easily. This may, in some people, cause a severe skin reaction and rash. Other than a physical irritant, the hairs also contain chemical toxins which explain the similar sensations to that produced by plant species employing the same tactic. The most important consideration is of course to avoid disturbing the caterpillars, though their notoriety often sees them subject to pest control measures. Ultimately, it's important to remember they're a native species and are purely one of a great number with a toxic defence mechanism. 

Brown-tail Moth © Ben Sale

Brown-tail Moth larvae © James Duncan