92 NATURAL HISTORY. 



On passing to the pupa state the larva skin contracts more or less, and generally becomes much 

 shorter, at the same time that the two ends of the body become equally rounded, and thus the 

 whole assumes an oval form. Even the traces of the segments become much fainter, or almost 

 unrecognisable ; but in many the line marking off the lid, which will be thrown off for the escape of 

 the perfect insect, is to be seen distinctly towards the anterior end of the case. At first the 

 enclosed insect detaches itself from the larva skin, and thus forms a soft, more or less pulpy, shapeless 

 mass, on the surface of which, by degrees, the rudiments of the parts of the perfect insect make their 

 appearance. When mature the fly throws off the lid of its case by the action of the head, which 

 commonly acquires a sort of temporary bladder-like inflation for this purpose (see figure on p. 72). 



FAMILY XIX. SYRPHHLE. 



Although the insects of this tribe present an almost infinite variety of structure, they are 

 usually divided only into two great families, which are very distinctly characterised. The Syrphidau 

 form a family of tolerably uniform character, and it is in the second of the two groups that the 



great variety is displayed, although the whole are united by certain pecu- 

 liarities, and the subordinate types melt into one another. 



The Syrphidae may always be recognised by a very obvious though 

 apparently unimportant character, namely, the presence in each wing 

 of a peculiar false vein, intersecting the short cross vein between the third 

 and fourth longitudinal veins. The longitudinal veins themselves do not 



generally reach the margin of the wing, but terminate in fine veins which unite them, and usually 

 run parallel to the margin, cutting off a narrow border. The antennae are three-jointed, with 

 an apical or dorsal bristle, which is in some genera beautifully feathered ; the eyes are large, meeting 

 in the males ; the ocelli are three in number ; the proboscis usually short, with fleshy end-lobes, 

 and enclosing three bristles besides the labrum, the maxilla? being free ; the palpi are formed of a 

 single joint, and are not prominent; the abdomen consists of five segments, and is flattened, 

 and occupied, to a great extent, by air sacs ; and the tarsi have two pulvilli. 



This family consists for the most part of elegant, brightly-coloured flies, remarkable for their 

 rapid flight, and for the ease with which they hover in the air over flowers. During flight many of 

 them produce a loud piping or buzzing sound. They are of moderate or considerable size, and 

 occur abundantly in all parts of the world. The surface is sometimes naked and shining, sometimes 

 hairy, and in the latter case the insects have a bee-like appearance. They are constantly seen about 

 flowers, upon the juices of which they feed, and are particularly partial to the flowers of the Composite. 

 Notwithstanding the uniformity of the characters and habits of the perfect insects, the larva* 

 exhibit a considerable diversity in both respects. Some of them are aquatic in their habits ; but the 

 majority live out of the water, some feeding upon the roots and 

 bulbs of plants, others living in decaying wood, in mud, and even in 

 sewers, others again being parasitic in the cells of Wasps and 

 Humble Bees, while a considerable number crawl over the leaves and 

 shoots of plants, and co-operate with the larvae of the Neuropterous 

 Hemerobiidae in the destruction of Aphides. 



The last-mentioned habit is displayed by the larvae of the 

 typical genus Syrphus and its allies. These are the prettily banded 

 flies which may be seen everywhere in gardens and in the open 

 country throughout the summer, often hovering motionless for a SYRPHUS PYRASTRI (A) LARVA (K), 



. , ? AND PUPA (c). 



considerable time over some object, such as a flower, but darting 



off with remarkable rapidity when disturbed, and often returning again and again to the same 

 spot. There are some thirty British species of the genus Syrphus, and most of them are 

 abundant and widely distributed. One of the commonest is the Syrphus pyrastri, an insect 

 about half an inch long, of a blue-black colour, with a stripe on each side of the thorax and 

 the scutellurn tawny, and three whitish or yellowish bands, interrupted in the middle, upon the 

 abdomen. The wings, as is usual in these flies, are colourless and transparent ; the halteres are 

 yellowish, and the legs are yellowish, with the thighs more or less black. By many people these 

 harmless flies are mistaken for wasps, and some of the allied species are particularly wasp-like. 



