DIPTERA > NEMATOCERA | Lower Diptera

BIBIONOMORPHA > Sciaroidea > Cecidomyiidae (658 species)

(subfamilies: Cecidomyiinae, Lestremiinae, Micromyinae, Porricondylinae and Winnertziinae)

As the collective common name of this family implies, the larvae of most species feed on living plants inducing abnormal growths known as galls. There are around 550 species in Britain that fall into this category producing galls of various shapes and structures on the leaves, buds and stems of a wide range of plants. The adults are tiny and rarely seen or photographed by the casual observer, which is why most references to the Cecidomyiidae only show photos of the galls; an example of which can be seen below. All of these phytophagous species are in the large Cecidomyiinae subfamily, which is subdivided into numerous tribes. There are also a small number of endoparasitoids of other insects and a couple of genera that are known to prey on aphids or mites, but the vast majority are true gall midges.

But, there's another group of Cecidomyiidae species that are better referred to as wood midges as their larvae feed on fungal hyphae growing on rotting deadwood or similar decaying plant tissue rather than developing within galls on living plants. These mycophagous, or fungivorous species as they are also known, are classified within subfamilies Lestremiinae, Micromyinae, Porricondylinae and Winnertziinae. I think, although I could be wrong, that you're more likely to find species in the first two - Lestremiinae that includes just eight species in three genera, and Micromyninae that is now treated separately. The Micromyninae includes over fifty species split into various tribes and genera. The remaining thirty or so species are in the other two subfamilies, Porricondylinae and Winnertziinae. 

There's a good set of keys to assist with identification and, given that there's probably more chance of seeing and photographing a wood midge than a gall midge, it's useful to know that there are a couple of visual features that, despite their tiny size, can be seen in well detailed photos. Obviously, it's not possible to identify the actual species from photos, but knowing for instance that ocelli are absent in all the Cecidomyiinae phytophagous species as well as in the Porricondylinae and Winnertziinae, means that if that detail is evident the individual in question has to belong to either the Lestremiinae or Micromyinae. That feature alone can provide a good starting point, but the primary identifier is the wing venation particularly the M vein; the presence and form of which together with the extent of the thicker part of the costa and other details, such as the 2+20 multi-segmented antennae, were used to tentatively ID the species featured below.

The family as a whole are described as being typically minute to small, delicate midges, that are rarely much more than 3mm long although a few species can reach as much as 8mm, with long legs and long conspicuous antennae that usually have 12-14 segments, although sometimes less, and certainly in the case of Aprionus considerably more; the wings, which are usually clear, and relatively broad, are usually hairy and fringed around the margin; the wing venation is much reduced with, apart from the single species in the Catochini tribe, no more than four primary veins reaching the margin; the costa continues further around the wing than normal and usually has a break just beyond vein R5.

Updated, Aug.24 (v.3)