Sawflies have two pairs of wings that are usually transparent but may have dark markings. The antennae are thread-like in most species but a few sawflies have clubbed antennae. Sawflies vary in colour, many are black and/or yellowish brown, some have yellow-banded abdomens.
The larvae of sawflies have a caterpillar-like appearance and resemble the larvae of butterflies and moths. All sawfly larvae are plant feeders. Most eat the whole leaf but some graze the leaf surface while some mine inside leaves. A few sawfly larvae feed inside developing fruits or live as stem borers. Most sawfly larvae are solitary feeders but some, particularly many of the pest species, feed gregariously. When disturbed, many sawfly larvae grasp the leaf edge with their thoracic legs and thrash the rear end of their body up and down, forming an S-shape. Most sawflies overwinter as fully fed prepupal larvae in the soil and they pupate in the spring a few weeks before the adult insect emerges.
The smallest adult sawflies, such as those species with leaf-mining larvae, are about 3mm long. Most species are in the 5-20mm range.
Sawflies can be found throughout Britain although some species have a restricted distribution.
There are just over 500 species of sawfly and other Symphyta in Britain.
Conifer and deciduous woods, grassland, bogs, gardens.
Where to find them in the garden
Some adult sawflies will visit flowers to feed on pollen, nectar or other insects. They prefer umbelliferous flowers, such as fennel, hogweed and parsnip. The caterpillar-like larvae are plant feeders and can be found defoliating plants such as gooseberry, Aquilegia, Solomon’s seal, Aruncus dioicus, roses, Berberis and willows.
Role in the garden
A minority of sawfly larvae can be damaging garden pests. In addition to the species that eat leaves, there are also species whose larvae feed inside the fruitlets of apples and plums. Some leaf-mining sawflies have larvae that feed inside the leaves of birch, alder, Geum, oak, elm and sycamore, causing brown patches in the leaves. Other sawflies cause distorted growth on their host plants, such as the rose leaf-rolling sawfly and bean gall sawflies, which create hard, bean-like swellings in willow leaves. Sawfly larvae provide food for birds and other insect feeders; they are also attacked by parasitic wasps and flies.