THE DIPTERA OF SUFFOLK (Continued from Vol. X I , Pt. I, page 58) FAMILY xxix:
SYRPHIDAE
HOVER-FLIES
First P a r t : by W.
Syrphinae and Chysotoxinae
S . GEORGE a n d A . E .
ASTON
THE Syrphidae are a family to which belong many of the more striking of our flies, both in colouring änd in their habit of hovering motionless in the air, some species low amongst the herbage others six to ten feet from the ground, where they form a splendid and often metallic sight in a spring glade. Clear against the sky the hover-fly remains quite steady until an intruder arrives to be chased off the territory and the hoverer returns. Syrphids are often to be seen visiting flowers and have been called " Flower Flies " on this account, but it must not be imagined that such a habit is a mere luxury, for Schneider in 1947 (Mitt. Schweiz, ent. Ges. 20 : 306-16) demonstrated that intake of pollen and nectar was necessary for maturation of the ovaries in certain Syrphidae. Mr. Parmenter has shown (Ent. mon. Mag. 88 : 50) that some Syrphidae have a preference for yellow colours in flowers and Dr. T . J. Dixon has demonstrated that Syrphidae prefer to oviposit on green stems (Trans. R. ent. Soc. Lond. Vol. III, p. 57). T h e adult flies vary considerably through the sub-families; almost all species, however, show a characteristic fold in the wingmembrane—a " false vein " (vena spuria)—the possession of which shows a fly to belong to this family. Many of the flies are striped with yellow and black, more or less resembling wasps and other hymenoptera but they can be distinguished by their Aying straight to their goal whereas Hymenoptera tend to follow a zig-zag path of continous motion much harder to observe. In most species of hover-fly the eyes of the males meet at the top of the head, forming a distinction from the females, whose eyes are separated by a narrow space. As larvae their habits vary remarkably between sub-families, though those of many species are little-known or completely unknown. Larvae ränge from the carnivorous Syrphinae, which eat greenfly and other aphids, to the vegetarians of the Cheilosnnae, which live in plant-tissues. T h e scavengers of the Volucellinae consume the waste in bees' and wasps' nests, while many of the Eristalinae are aquatic and live on organic debris in stagnant water—in fact there seems no basic larval type for the family.