30-Jul Night Wings: London’s Moths & Their Vanishing Magic

Wimbledon Common might be a reasonable place to start, with more than a hundred different species recorded from moth traps there this month. As a rule, moths prefer drier areas and more open patches of woodland, although we do tend to see many at bright windows or circling around street lights. Unfortunately, studying London’s moths is a depressing affair, with so many having become rare or extinct, but there are still enough to keep any entomologist busy for at least one lifetime.

Amongst the most beautiful of all moths are the tigers, which are often mistaken for butterflies. Sadly, the Scarlet, Wood and Cream-spot tiger are all now extinct in London, although the latter sometimes turns up as a vagrant. However, London still has two i.e. the Ruby and the Garden tiger. The former has finished flying by June, but the Garden tiger flies from mid June to mid August. Although it occurs all over the city it seems to have a preference for east London. It is unmistakable with its deep chocolate and creamy white forewings and brick red hindwings, with inky blue spots. These warning colours deter birds, which seem to find them distasteful and consequently the moths seem to make little effort to hide away during the day. A rare form with a completely red abdomen has been recorded at Addington and there are others which show more orange or even primrose yellow.

Closely related to the tigers are the equally impressive ermines. It is the white ermine we tend to see in London, which is a dazzlingly white with numerous black spots as its name suggests. It is both common and widespread and always gets noticed when seen at rest, which may even be in central London. They fly in the first half of the month, whereas the equally common buff ermine can be seen the whole of July. This latter species is more of a buff yellow, with just a few dashes and dots on its wings.

There are seventeen species of hawkmoth that either live here or visit Britain and all of them have been recorded in London at one time or another. They are unmistakable large, fast flying moths with fat bodies and pointed wings which are either brightly coloured or finely patterned. They catch our attention mainly because of their fast flight. The hummingbird hawkmoth has been confused for an actual humming bird as, like other hawkmoths, it can hover with blurred wings in front of flowers, projecting its long proboscis to suck the nectar. This is a powerful insect, capable of flying over one hundred miles a day from its home in southern Europe to reach our gardens here in Britain.

The more common hawkmoths seen last month i.e. Lime, Eyed and Poplar, all cease to fly in July. The elephant hawkmoth ceases in the first week although the less common small elephant hawkmoth may continue to the middle of the month. The pine hawkmoth just makes occasional rare appearances.

The eggars are another small but impressive group of moths. They tend to be large and brown with some having the egg-shaped markings which give the group its name. They include such famous names as the oak eggar, the drinker, the lackey and the lappet. The latter seems to have disappeared, possibly due to the removal of many of the blackthorn hedges which its caterpillars feed on. The oak eggar is possibly the best known as it flies during the day, with a distinctive zig zag flight on heaths or along woodland edges, trying to locate a female’s scent plume. It is a large, brown moth with a pale yellow band across its wings and two bright white ‘eyes’ lined in black. In the case of the drinker it is the caterpillar which is responsible for its name due to its habit of drinking dew drops. The adult male is reddish brown and the female more yellow. Both adopt a distinctive paddle shape at rest and have a fine line crossing the centre of their wings as well as two small ‘eyes’ on their forewings. Occasionally the sexes swap colours, but can still be told apart looking at their antennae. The male has large, feathery antennae and those of the female are much smaller and indistinct. The lackey is similar to other eggars, but has two fine parallel lines crossing its wings rather than one. It also has a chequered edge to its wings. It prefers open areas, but does visit central gardens where sometimes its caterpillars can reach pest proportions.

Another larger and more important group of moths, which are particularly abundant at this time of year, are the geometers. They get their name from the way their caterpillars move with geometric precision. These are the familiar looper, stick, earth measurer or inchworm caterpillars we saw earlier in the year, but now we can see the adults. They look a little like butterflies, having such large wings and small bodies. Although they tend to be dull in colour, many do have fine patterns and spotting. The family is huge, including large numbers of pugs, carpets, waves as well as browntails, emeralds, underwings, beauties, ushers, umbers, mochas, heaths and thorns. The species that tend to catch our attention are the more striking emeralds, underwings and magpie moths as well as the Brimstone, Engrailed, Barred straw, Barred yellow, Purple thorn and Peppered moth. Particularly common and widespread species include the Riband wave, Small fan-footed wave, July high flyer and Willow Beauty. The latter is often caught in large numbers, especially if there are any willows around.

One of the most beautiful geometers is undoubtedly the swallowtail. It is unmistakeable with its pale yellow wings with crosslines and pointed tips to its hindwings. It is often seen in overgrown cemeteries where its food plant, ivy, is covering the monuments. The Magpie is also known as the Currant moth, as it shows a marked preference for gooseberries. Both the caterpillar and adult have distinct black, white, orange, yellow and cream markings. The silver grand carpet has pearly wings with a dark crossband and is usually found where primroses are common. The Willow beauty is usually brown, but there is also an attractive smoky-grey form in the London area.

Its caterpillars are unusual, choosing to eat the normally poisonous yew. The Purple thorn is another attractive species worth looking for. It has jagged edges to its wings like other thorns but has more purple rather than the usual yellow brown colours of other thorns. Its stick-like caterpillars are often seen on sycamores.

Few adult moths or even butterflies produce a pure green pigment, even though there are hundreds of different green caterpillars. Another group of geometers, the emeralds, are the exception. The Large emerald is the most impressive. It prefers birch woods, although it is found in gardens as long as there are is some birch around. Like most emeralds, it is a pale green, which really stands out, especially when seen in moonlight. The Blotched emerald conveniently has two brown blotches on its green wings which help to distinguish it. It prefers oak woodland, whereas the Small emerald is more likely to be seen on downland. The Common emerald is both common and widespread and seems to favour gardens. Its jade green quickly fades to grey green, making it easily confused with the Little emerald, which is slightly smaller and usually much lighter in colour. Lastly in this confusing group, the Grass emerald tends to be more of a blue-green, but also is the only one to have dark cross lines on its wings. It can often be encouraged to show itself by gently tapping gorse bushes on heaths.