Highgate Wood's hundreds of moth species 'as colourful as butterflies'
- Credit: Michael Hammerson
Moths – “Small nocturnal insect breeding in cloth, etc, on which its larva feeds”
Thus my 1964 Concise Oxford Dictionary dismissed one of our most fascinating and colourful groups of wildlife.
As a result, some people’s reaction to the news that over 370 species of moths were recorded on Hampstead Heath in 2019, and nearly 450 in Highgate Wood over the past 35 years, might be to spray their clothes before coming for a walk.
Yet of the 2,500 species of moths recorded in Britain, only four eat clothes; they evolved to eat feathers and other debris in birds’ nests, discovered the tasty woollen items we provided for them in our houses, but never evolved to learn that they aren’t meant to eat them. As a result, millions of innocent moths are killed by people who should know better.
My 35-year survey has recorded nearly 450 species in Highgate Wood. They are attracted at night to a powerful light trap, examined in the morning and set free unharmed (though not all moths are attracted to light; many are day-flyers and spotting them is much more a matter of luck). Information about them is displayed in the wood’s information hut.
Most of the 800 “larger” moths found in Britain are fairly easy to identify, though variability, the similarity of closely-related species, and the problem that many don’t resemble their photographs in the textbooks, can make identification tricky.
The Victorians gave them English names on top of their scientific Latin names; exotic names include the Kentish glory, argent and sable, seraphim, phoenix, Barrett’s marbled coronet, footmen, Foresters, carpets and lackeys and, to confuse us, a bright-line brown eye and a brown-line bright eye.
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Unfortunately the majority – the so-called “micros” – only have Latin names, are often tiny, sometimes impossible to identify without a microscope, and books enabling the amateurs among us to identify them have only recently been available.
Moths, like butterflies (there is no real difference between them, by the way), need their own particular food-plants on which their caterpillars feed. Some are catholic in their tastes, while others would literally rather die than eat the wrong plant. Some even eat roots, fungi and decaying wood, and many need specific ecological conditions.
They appear at different times of the year; a few even fly in winter. Most found in Highgate Wood are quite common, but 450 mainly common species – nearly 20% of the total – show the wood is healthy. Others, like those needing rare plants or habitats, will never be found at Highgate. Some are so rare that they are only known from a few sites.
Many, including some hawk moths and the familiar silver Y, are annual immigrants from the Continent; some are very rare, like the Dewick’s plusia found in the wood this year. Until about 20 years ago, the colourful Jersey tiger was found only on the Channel Islands and the Devon coast, but it suddenly appeared in London.
The oak processionary moth, introduced with imported oak trees for gardens, has become a serious pest on the Heath; its larvae can strip trees and their hairs cause bad skin rashes. Fortunately a predator fly has followed it from the continent and is starting to control it.
Their numbers fluctuate annually, due to climatic factors, abundance of predators, disease, etc. The oak tortrix moth used to come to the wood’s light trap in thousands; in recent years it has almost disappeared, as has the winter moth: bad news for birds seeking food for their fledglings.
The large yellow underwing, once the wood’s commonest moth, almost disappeared and then returned, showing how nature is cyclical. The awkwardly-named Svensson’s copper underwing is rarely found in our moth-trap; but oddly we find them in large numbers in bat-boxes, though moths are a major food for bats.
Swarms of tiny shimmering bronze-winged moths flying in the oak canopy in spring are members of the longhorn moth family. The attractive, and superbly-camouflaged, tree-lichen beauty, until recently a rare immigrant, is now resident in the wood.
The spruce carpet moth is a curiosity; usually found in conifer woods, it appeared in Highgate Wood when they introduced Christmas Tree recycling.
Look out for curious blotches and squiggly lines on leaves. These are caused by caterpillars of the tiny “micros”, so small that they live and feed in a “mine” between the upper and lower surface of a leaf. Some adults are masters of camouflage; others flaunt bright colours to warn predators they are poisonous.
Though thought of as not nearly as colourful as butterflies, these photographs (not to scale) show that this is far from the case.
Crucially, they are a vital part of the food chain, for birds, bats, amphibians and predatory insects; only about 1% of eggs laid reach maturity. They are also major pollinators.
Many are now in decline or threatened, and their habitats need careful management. So, next time one flaps through your window and spirals round the light, don’t destroy it with a rolled-up newspaper.
Gently catch it in a box or glass, and put it outside. Remember, too, that gardens are a critical part of the local ecological corridor; grow suitable wild plants grow in your garden for the larvae and adults to feed on.
Michael Hammerson, Heath and Hampstead Society.