|Artist's fungus (Ganoderma applanatum) and galls © Judy Webb|
A gall can be caused by bugs such as types of aphid, mite or wasp, or by viruses or bacteria. Under the influence of the invader, the plant is prompted to produce a series of abnormal growths which will provide food and shelter for the invaders young. Galls do not usually cause plants long term damage or cause them to die.
The yellow flat-footed fly (Agathomyia wankowiczii) is unique in its ability to cause a gall on the Artist’s Fungus (Ganoderma applanatum) - a fungus commonly found in woodlands on deciduous dead wood. The Artist’s fungus is a hard fungus which grows slowly enough for the fly to lay its eggs and harbour the growth of the offspring before the fungus decays. Because of this it is the only host that can support this insect. Astonishingly this is currently one of the only insect and fungi gall combination known in Britain!
The gall is found in large clusters on the whitish underside of the fungus. They start as small warts that can grow up to 1cm in height. Inside each wart is the grub of the fly. Once the grub is fully grown it bores a hole into the top of the gall and falls to the ground where it buries its self into the soil before it pupates to turn into the adult fly.
|The Yellow Flat-footed Fly (Agathomyia wankowiczii) © Judy Webb|
The fly is the only entirely orange species of flat-footed fly in Britain, although there are thirty species of these flies in total. The 'flat-footed' part of the name comes from the fact that part of the hind foot is flattened. Adult Yellow Flat-footed flies can be seen running around on the surface of tree leaves, especially at wood edges and on sunny spots in the dappled light of a woodland.
How you can help
The Yellow flat-footed fly was only recently discovered in Britain. The adult fly is rarely seen so it is easier to search for the galls (which are easily overlooked because they are on the underside of the fungus). At present very little is known about the distribution of the gall. Please send any digital photographs and locations of this gall to firstname.lastname@example.org.