On the production of silk by species of the genus H ilara meig. (Diptera)

Abstract

In the Entomologist's Monthly Magazine for 1877, p. 126, there is a note by Baron C. R. Osten-Sacken describing certain species of the genus Hilara which, in flying, carried with them “bits of white tissue.” These objects, on closer examination, proved to be flakes of “opaque, white, film-like substance, oval, about 2 mm. long, and so light that the faintest breath of air could lift them.” He describes the appearance of the film as not "unlike the opaque white tissue spun by some spiders.” The species of fly was identified as Hilara alpina , Loew, by Prof. Loew, who also informed Baron Osten-Sacken that Prof. Zeller had made a similar observation on August 14, 1873, near Bergün. The foregoing account appears to include the first recorded observation on the habit of silk-spinning in the genus. In regard to the name alpina, the original identification of the film-making species is questioned by Becker ( Berlin Ent. Zeit ., 1888, p. 7) and he gives to it the name of Hilara sartor , and appends a full description of the two sexes. He supposes that the secretion is produced from the abdominal glands. In 1889 ( Ent. Nadr ., p. 220) Girschener described the webs made by H. maura , Fab., and H. interstincta , Fall., and pointed out that they sometimes contained the insect prey of Hilara. Later, Mik added the species H. aëronatha to the list of those which carried prey. Handlirsch (in Verh. Zool.-Bot. Ges ., Wien, 1889, p. 624) further described, with much detail of measurement, the webs or veils made by H. sartor . He gives the diameter of the threads as 0·001 to 0·0015 mm., and states that the silk is similar in chemical composition to that of caterpillars and spiders.