You will likely see one of the five hundred species of swift moth fluttering around the garden on a warm evening in June or July, soon after the sun has gone down.
Swift moths comprise over 500 species, with a wingspan of up to 7 inches in some. The ghost moth is named after its coloring and pendulum flight, giving it a ghostly appearance. Caterpillars of swift moths grow underground to keep themselves from predators and are drab in comparison to many other families of moths.
The ‘swifts’ (family Hepialidae) are a primitive family of moths which includes the well-known ghost moth, renowned for their tiny tongues and unusually short antennae.
Although they are most common in Australia, where some species have wingspans as great as 18cm (7in), five beautiful species do occur in Britain and Ireland.
On a warm July evening, soon after sunset, while it is still light, you can sometimes see a silvery-white moth flying over flower beds looking ghost-like.
The male ghost moth is named after its coloring and flight mode, which resembles a pendulum.
The female is quite distinct from the male in appearance and flight as her wings are yellow with orange markings, and she has a direct flight path, unlike that of her partner.
Variations occur, some of which can be found in the Shetland Islands. Some males have brownish-orange markings on their forewings and dark hindwings, while others resemble mainland females.
While the significance of this coloring is not fully understood, one possible explanation is that, since they evolved isolated. At high latitudes where the July nights are short and the vegetation scarce, the all-white males developed their coloring to blend with the different environments.
The ghost moth occurs all over the British Isles and is abundant in various habitats, including graveyards, gardens, fields, woods, and even urban wastelands where the growth of weeds provides ample camouflage.
Here the adults are sometimes found by day, resting on the vegetation. If disturbed, they fall to the ground and feign death by keeping completely still.
They can normally be seen flying around just after sunset, but if you search carefully in the daytime, you may find one hiding among the plants. The male looks like a piece of white silk caught on a plant, and the female resembles a leaf.
To protect herself from birds, she remains so still that from a distance, she resembles a withered leaf. However cautiously you approach her, she will almost certainly disappear, either by falling into the vegetation, as if dead or by rapidly flying away.
Where Do Swift Moth Caterpillars Grow?
Swift moth caterpillars spend all their life underground, so you are unlikely to see them except when digging up plants in the garden. The pupae also stay underground in cocoons constructed of silk and soil particles. Unlike most moth pupae, they are active and wriggle violently if disturbed.
In most moths, the courtship starts when the male is attracted by the female’s scent. In ghost moths, however, the opposite happens, with the female playing the role of the chaser, attracted by the male’s scent, which resembles the smell of a goat.
Following courtship and mating, the female scatters her eggs randomly over the vegetation, usually in July. The caterpillars soon hatch and begin feeding on the roots of almost any herbaceous plant, attacking garden varieties and crops as well as wild species.
The caterpillars slowly grow through the autumn and winter and are not fully developed until the following May. In contrast to the larval stage, the pupal stage lasts only a few days, during which the pupae work their way to the surface before the adults finally emerge.
The most abundant member of the Hepialidae is the drab-looking common swift. If you are lucky, you may see hundreds of this species flying at speed through the vegetation on warm summer evenings between June and September.
The caterpillars are white and live underground, where they feed on the roots of grasses and other plants throughout autumn and winter. Since they exist in such large numbers, the damage they cause to roots and grassland can be so extensive that they are sometimes considered pests.
Are Swift Moths Colorful?
The orange swift is a more attractive-looking species. The male has bright orange forewings with white bars, while the larger female is brown with deep chocolate-brown and whitish markings on her forewings.
The caterpillars take about two years to mature, reaching full size in the autumn. They then overwinter in the soil and pupate the following spring.
The gold swift is more common in woodland, but only if there is an abundance of bracken, as the caterpillars feed on the roots and mature two years later. The male gold swift is similar to the male orange swift. The female is similar to the male but duller.
Gold swifts are not as common as the previous three species, but the male can be easily spotted as it flies in the same pendulous manner as the ghost moth.
Another species, the mapwinged swift, is named after the pattern on its wings. They can be found on heathland, open woodland, pastures, and moorland.
The yellowish-white caterpillar feeds on bracken roots and the roots of red fescue. They are fully grown in May, and the adult moth flies at dusk in June and July.
The caterpillars of the ghost swift and other swift moths are whitish. They feed underground on roots, concealed deep down so most birds can’t find them.
They do not need the protective coloring found in the caterpillars of many species living above ground. Above-ground caterpillars are either cryptically colored for camouflage or are boldly colored and conspicuous to advertise the fact that they are distasteful.
Camouflaged caterpillars usually escape detection by day unless they give themselves away by the movement and normally feed safely and unseen by night.