It is also possible that these small flies are connected with the formation of “Delhi boil,” caused by a protozoan parasite.
Fig. 404.—An owl midge, Phlebotomus sp. Greatly enlarged. (From Giles’s “Gnats or Mosquitoes.”)
Psychodidæ are all very small flies, many of which have a moth-like appearance, and owing to their fluffy nature are spoken of in Britain as “owl flies,” sometimes also as “window flies.” Their bodies and wings are covered with hairs, densely in some (sub-family Psychodinæ), and in a few with patches of flat squamæ. In the non-blood-sucking Psychodinæ the wings are carried in a peculiar manner downwards over the body, to a slight extent resembling the Hepialidæ, or swift moths. The wings may be ovoid or lanceolate, and have a marked venation as seen in the figure. The proboscis is short and non-suctorial in the majority of genera, but in the sub-family Phlebotominæ it is elongated and hard. The antennæ are long and of sixteen segments, and bear whorls of fine hair.
There are two sub-families, Psychodinæ and Phlebotominæ; in the former the mouth is not suctorial; the female has a horny ovipositor and the second longitudinal vein is branched at the root of the wing; in the second sub-family the proboscis may be formed for sucking, the female has no horny ovipositor, and the second long vein has its first fork near the middle of the wing.
The sub-family Phlebotominæ contains the genus Phlebotomus, which occurs in South Europe, South Asia, Africa, North and South tropical America. They are all small grey, brown, or dull yellow-coloured flies, and carry their wings when at rest upwards like a butterfly. The proboscis is moderately long and the legs long and thin.
The females are most vicious blood-suckers, but in some species anyhow the males also bite (P. duboscii). They are mainly nocturnal feeders and hide away during the day in any dark corners or crevices.
The life-cycle has been worked out by Newstead[403] and Grassi[404] in Europe, and by Howlett[405] in India.
The larvæ have been found in crevices in rocks and caves, in dirty cellars, and dark damp places containing rubbish, and are also said to live in crevices in the walls of privies and cesspits.