Trees

Trees

Trees provide food and hibernation sites for caterpillars
and aphid honeydew for adult butterflies.

Butterflies are often associated in our minds with wild-flower meadows or flowery gardens but a high proportion of British butterflies live in woodland, eating the leaves and drinking the nectar of woodland flowers.

Several are actually tree dwellers with caterpillars that eat the buds and leaves of trees, and adults that feed on aphid honeydew.

At least one species, the Goat Moth, takes things to extremes. Instead of feasting on the buds and leaves of the tree, the caterpillars feed on the bark and trunk. The adults don't eat at all.

DECIDUOUS TREES AND NATIVE CONIFERS ADD ENORMOUSLY TO BIODIVERSITY AND MUST BE PRESERVED, AND THEIR NUMBERS INCREASED.

Trees like Oak and Elm take a long time to reach maturity, but we can all find a space for fast growing species like Willows, Blackthorn and Buckthorn, which are readily available from hedging suppliers.

WYCH ELM
Ulmus glabra

The WHITE-LETTER HAIRSTREAK (Strymonidia w-album) is dependent on elm trees (Ulmus spp.) so not surprisingly it became a collateral victim of Dutch elm disease,

Numbers plummeted with the destruction of so many of its trees, but fortunately its favourite elm is Wych Elm which has not suffered so badly as the other species, and is still to be found in localised areas throughout England north to Yorkshire.

The female strongly prefers to lay her eggs on the flower buds of freely-growing trees rather than those in hedgerows, a good move as hedge-cutting can have disastrous consequences for caterpillars and pupae alike.

The adult always rests with its wings closed, when white lines, often in the shape of the letter 'W', from which it gets both its common and Latin names, are visible. It has small ’tails’ at the ends of its rear wings.

​It feeds mainly on aphid honeydew, occasionally descending to feed on the nectar of nearby flowers.

OAK
Quercus spp.

The striking PURPLE HAIRSTREAK depends for its survival on oak trees, as reflected by its Latin name Favonius quercus.

The female lays her eggs singly at the base of a flower bud, the emerging caterpillar feeding on the bud and moving at a later stage to the young leaves.

Adults feed primarily on aphid honeydew, and are occasionally seen taking nectar from bramble.

When in flight, its black upper wings flash silver and white on catching the sun.  At rest with its wings closed, it can be distinguished by the white streak on its silvery-grey underwings.

Clearly anything that results in the felling of oaks – replacement by conifer plantations, road and house building etc. – will have a negative impact on this oak-dependent butterfly.

The Purple Hairstreak occurs throughout the UK but is most common in the southern half of England and in Wales.

BLACKTHORN
Prunus spinosa

A variety of native shrubs also serve as the caterpillar foodplants of butterflies. One such shrub is Blackthorn, also known as sloe, which is favoured by the BROWN HAIRSTREAK (Thecla betulae) despite the butterfly's Latin name being suggestive of birch trees.

The adult feeds on aphid honeydew. When resting with its wings closed - it sometimes rests with them open – a long white streak is visible on the underside. The female is a richer gold colour than the male with a longer ‘tail’ protuding from the rear wings. 

The female doesn’t favour isolated plants but usually lays her eggs on Blackthorn growing along wood edges and in hedgerows.
It is one of very few British butterflies that overwinters as an egg, with the caterpillars emerging the following spring to feed on the Blackthorn.

Scattered colonies are to be found in England, Ireland and Wales in areas where Blackthorn grows.

BUCKTHORN

Purging Buckthorn (Rhamnus cathartica) and Alder Buckthorn (Frangula alnus) on wetter soils, are the foodplants of caterpillars of the BRIMSTONE butterfly.

It is found throughout England up to the Lake district, and in Ireland and Wales, wherever buckthorn grows.

The PURPLE EMPEROR (Apatura iris)
This is another butterfly of woodland. Its larvae feed on the leaves of Sallow willows (Salix spp.) especially Goat Willow (Salix caprea), while the adults feed mainly on aphid honeydew.

The GOAT MOTH (Cossus cossus)
This moth feeds on trees, not on the juicy buds or leaves but on the markedly less appetising bark and trunk of a wide range of deciduous trees.

The female lays batches of eggs in crevises in the bark, behind which the emerging caterpillars feed before burrowing into the harder timber beneath where they eventually form a network of tunnels.  There they stay for three or four, even five years before, at 40 to 60mm in length, they emerge to pupate and develop into mature moths with a wingspan of 64 mm to 84 mm. This makes it an exceptionally big and long-lived lepidopteran, as most butterflies and moths complete their whole life-cycle in less than a year; often only about two months in the case of the first brood of the season, the final broods spending most of their lives in hibernation.

As it feeds, sap, as well as frass and sawdust, drips from the entrance to the hole which can be 20 mm in diameter, and it's the sight of a Purple Emperor butterfly or other honeydew eater having a change of diet that often alerts one to the presence of the Goat Moth larvae.

Having escaped from their subterranean existence in the tree-trunk you might expect the adults to celebrate with a stiff drink of flowery nectar, or at least honeydew, but adult Goat Moths do not feed at all. The mouthparts in the caterpillar which were adapted to tough chewing don't develop into nectar sucking proboscises.

The Goat Moth is widespread throughout the British Isles, but rare enough to be designated a Biodiversity Action Plan priority species. The 'Goat' in its name refers to the smell of its caterpillar being likened to that of a goat.