THE MUSCIVM. 93 



Their larvae, which are footless grubs, generally much wrinkled across, live upon the leaves and 

 twigs of plants which are infested by Aphides, in pursuit of which they crawl along upon, their flattened 

 under surface in a manner which somewhat reminds one of the movements of a common slug. 



o 



They are narrowed in front, and have no distinct head, but the mouth is furnished with a sort 

 of trident with which the larvae transfix the Aphides and suck out their fluids. When full 

 grown the change to the pupa takes place within the larva skin, which remains attached to a 

 leaf or twig, and hardens in the usual way. As the parent flies always lay their eggs singly in 

 the midst of colonies of Aphides, the larva when hatched has of course an abundant supply of 

 food at its command ; its growth is in consequence rapid, and there are several broods of the 

 flies in the course of the summer. By their destruction of Aphides they must be regarded as 

 conferring an important benefit upon the farmer and gardener. 



The VolucellcK (see PI. 62, F), which are nearly related to the Syr phi, but are of a stouter form 

 of body, and less gaily coloured, reside in the larva state parasitically in the nests of Wasps and 

 Humble Bees, and sometimes they mimic the appearance of the insects in whose dwellings they are. 

 unbidden guests in a most remarkable manner. This is especially the case with a common British 

 species ( Volucella bombylans), which infests the nests of Humble Bees ; it is black and hairy, 

 precisely resembling a small Humble Bee, about half an inch long, and, curiously enough, it even 

 varies in the colour of the hair on certain parts of the body, and this very much as in different 

 species of Bees. The larva has the body much wrinkled, 

 and along each side a double row of short spines, while 

 four or six longer spines radiate from the broad and 

 rounded hinder extremity ; and below there are six pairs 

 of tubercles, each with three claws, which may be regarded 

 as prolegs. These larvae feed upon those of the Bombi and 

 Wasps whose nests they frequent. 



A considerable number of the species, however, appear 

 to feed on vegetable matters, either fresh or in state of 

 decay ; the larvae of several species feed on the bulbs of 

 plants (some on those of Narcissus) ; others, forming 

 several genera, live among rotten wood. Of this number 

 are many species of the genus Eristalis, but that group ERISTALIS TENAX AND ITS KAT-TAILED LAKVA. 

 includes one species with an aquatic larva. It is a 



stout, pitchy black, hairy fly, over half an inch long, with the scutellum, the hind borders of 

 the abdominal segments, and a triangular spot on each side of the base of the abdomen tawny ; 

 it is met with abundantly everywhere in gardens and fields. The larva is a most singular 

 creature, having a somewhat ovate segmented body, furnished beneath with seven pairs of tubercles 

 armed with hooks, and terminated posteriorly with a long tail composed of two segments, one of 

 which slides within the other after the fashion of the joints of a telescope. This tail enables 

 the larva to communicate with the air for respiratory purposes when it is lying snugly concealed 

 in the mud at the bottom of some piece of stagnant water, which is the regular habit of the insect 

 in this stage. When full grown the larva quits the water and buries itself in the ground, where 

 the pupa is formed in the usual way within the larva skin. These larvae are commonly known as 

 " rat-tailed larvae." Their skins are exceedingly tough, and in allusion to this the species is 

 named Eristalis tenax. Helophilus pendulus, a nearly allied species, has a similar larva, with 



similar habits. 



FAMILY XX. MUSCID^. 



The remainder of the Athericera are generally regarded as forming a single great family, of which 

 the genus containing the common House Fly (Musca domestica) may be taken as the type. The 

 members of this family are, as already stated, very variable in their character. They have three- 

 jointed antennae, and these, except in one genus (Conops} which shows a strong relationship in other 

 respects to the Syrphidse, are short, have the third joint usually the largest and furnished with a 

 bristle springing from its back, and are commonly bent down in front of the face. The proboscis has 

 fleshy terminal lobes, and encloses only a single bristle besides the labrum ; the palpi generally project 



