Amongst the large family of Syrphidæ is found a section known as the Eristalinæ or drone flies, whose curious long-tailed larvæ are popularly called “rat-tail larvæ,” on account of the end of the body being drawn out into a long telescopic tail of two segments, at the end of which are placed the breathing pores. These larvæ live in water, no matter how foul, and in liquid manure. They have occasionally been obtained in foul drinking water by human beings and from eating watercress improperly washed or from badly kept beds. Austen (Trans. Soc. Trop. Med. and Hyg., iii, No. 6, p. 221) records that in the autumn of 1907 a number of the larvæ of the common drone fly (Eristalis tenax) were passed per rectum by a woman in Hampshire who had recently arrived from France. The patient had eaten a considerable quantity of watercress before leaving France. I have twice found small Eristalis larvæ clinging by their long tails on watercress served at table.
Family. Drosophilidæ.
Small, rather plump flies, with short, broad abdomen, with bristles on the head and legs. Often abundant in decomposing fruit, and may occur in dense masses.
Drosophila melanogaster, Br.
The larvæ of this fly occur in over-ripe fruit and in fungi, often also in human habitations, and live in substances undergoing acid fermentation (vinegar, decaying fungi, rotting fruit, in damaged spots in diseased trees), much more rarely in animal substances, and they occasionally gain access to the human intestine (for example, by the medium of sour milk). When introduced in any quantity, they cause vomiting or attacks resembling colic; when taken in the pupal stage no unpleasant results are produced.
Family. Muscidæ.
Teichomyza fusca, Macq.
Syn.: Scatella urinaria, Rob. Desv.; Ephydra longipennis, Meigen.
The larvæ live in the urine in privies. Several authors state they have found them in fresh fæces or in vomited matter. Pruvot states that they continue for three days in the stomach of rats into which they have been intentionally introduced. (Pruvot, G., “Contrib. à l’étude des larves de dipt, trouv. dans le corps humain,” Thèse de Par., 1882; Chatin, J., in Comp. rend. Soc. de Biol., Paris, 1888 (8), v, p. 396; Roger, H., ibid., 1851 (1), iii, pp. 88, etc.)
Homalomyia canicularis, L., etc.