NATURE KNOWLEDGE

Press, Volume LXXII, Issue 21718, 27 February 1936, Page 2 (Supplement)

NATURE KNOWLEDGE

Isabella Bennett, Ashburton, sent a specimen of Syrphus novaezelandiae (Fig. A), and Alice Crampton, Rangiora, sent a larva of Erlstalis tenax (Fig. C). Both these species belong to the family Syrphidae, one of the largest and most sharply-defined families of the order Diptera. Popularly known as hover flies, the members of this family are moder-ate-sized to large insects usually of conspicuous colouring metallic browns and blacks spotted, banded, or striped with yellow or orange or creamy white, metallic greens

and green and red, and metallic blues. Some species are smooth and very shiny, some are densely hairy. Nearly all members of the family are attracted to flowers and may be seen poised in the air with wings vibrating with extreme rapidity, and anon they make sudden darts. Some species, particularly of the genus Syrphus, have the ability to hover developed to a remarkable degree: members of this genus approach the dragon flies m their powers of flight—besides their ability to hover, in which resoect they surpass the dragon flies, they also have the ability to fly. sideways at right angles to the line of the body for distances of a few inches, and to fly directly back-

wards for distances up to about 3 > inches; they can also rise vertically, for a few finches, with the body remaining in the horizontal plane. Speed of .flight is moderate to fairly swift. There are three main types of larvaC. 1. The aphis-feeding type, e.g. Syrphus, is rather flattened with the body tapering considerably towards the head and with very short posterior oir tail-end breathing tubes; the general appearance is rather slug-like. Larvae of this type are somewhat transparent and have a marked Capacity for changing their general shape; the common colouring is . some shade of - green, slightly marked i**^ orbrown<

HOVER FLIES (A.V.C.) .

2. The short-tailedT filth-inhabi-ting type has a cylindrical body with no taper and with short posterior breathing tubes. 3. The rat-tailed type, e.g. Eristalis, is more or less cylindrical with a long posterior, flexible, telescopic breathing tube which, in some species, can be extended several times the length of the body.. The head of a Syrphid larva is greatly reduced, situated at the small end of the body in species which taper. The skin of the body is tough or leathery, the segmentation obscure owin'* to the numer-

ous transverse corrugations. Most species have two pairs of spiracles or breathing openings—one pair on the anterior or, forward end of the body and the other pair at the hind end; in others only the posterior pair is present. The‘posterior pair is situated at the extremities of two tubes, of variable length, which are fused together. Larval habits are extremely varied. Seme species are carnivorous, preying upon aphids and scale-insects; such species suck out the soft portions of the body of their prey and leave the rest. Some are vegetarians, feeding externally upon plants or internally in bulbs, stems, and fungi. Some live in decaying organic matter, in dung, in dirty water, in liquid mud, in

the wet, rotting wood of diseased portions of trees. And others are scavengers in the nests of ants, termites, bees, and wasps. Some Syrphid larva pupate attached by the tail to d leaf or twig or such support, others bury themselves in the soil. The puparium usually has the appearance of being considerably inflated at back and sides. The adult generally escapes through a rupture or breakage in the back. Only a few of the Syrphidae are in any way injurious to man; .pests are the species which attack corn, and the bulbs of Narcissus- and Amaryllis. The larvae of a few/ more especially Erlstalis, occasionally occur as accidental parasites in the human body, causing myiasis of the intestine.

Some species are very beneficial, such as those which feed upon aphids and scale-insects. Syrphus novae-zelandiae, a very common native species, is a rather slender fly, black with small orange patches on the abdomen. The larva feeds on Aphis species. Eristalis tenax is a stoutly built fly, brown with yellow markings. An introduced species, it is always particularly abundant, about the flowers of Michaelmas daisy (Aster tradescanti). The brown larva inhabits the dirty mud of drains, etc., the telescopic breathing tube projects from the mud and enables tbe ereatnre to obtain, the necessary oxygen. For pupation the larva crawls ashore with the aid of the tiny hooked swellings on its undersurface and buries itself in the earth. Puparium—-See “The Press Junior,” November 28, 1935. Myiasis—See “The Press Junior,” November 28, 1935. Narcissus —The genus which contains the daffodils, etc.; family Amaryllldaceae. Amaryllis—The genus which contains the “belladonna lily”; family Amaryllidaceae. A CORRECTION In the Caddis-files article last week there was a mistake. The sentence “The cocoon Is commonly brownish or some shade of green” should have been “The pupa is commonly brownish or some shade ol green.” 1