DIPTERA. 



63 



commonly known as rat-tailed maggots, on account of the long tail-like appendages 

 at the hinder end of the body. With this flexible and telescopic tail, traversed by 

 tracheal tubes opening at its tip, the maggot is able to breathe while below the 

 water, by keeping the tip of its tail above the surface, where it is supported by 

 the rosette of hairs round the extremity. The eggs of drone-flies are also laid in 

 dead carcases and other refuse, and it is now believed that the legend of the ox- 

 born bees of the ancients is traceable to this habit of the fly, in conjunction 

 with its striking resemblance to the honey-bee. The belief that honey-bees are 

 produced by spontaneous generation from carcases of dead animals has pre- 

 vailed for more than two thousand years, but according to Osten Sacken, " the 

 original cause of this delusion lies in the fact that a drone-fly (Eristalis tenax) Lays 

 its eggs upon the carcases of animals, that its larvas develop within the putrescent 

 mass, and finally change into a swarm of flies, which in their shape, hairy clothing, 

 and colour look exactly like bees, although they belong to a totally different order 

 of insects." Scarcel}' less interesting than the drone-flies are the species of 

 Volucella. These large flies (p. 65, No. 9) mimic humble-bees in colour and form ; 

 ami it was long supposed that the females were thus enabled with impunity to 

 enter the nests of humble-bees and lay their eggs amongst those of the proper 

 owners. But although it is true that the eggs of the Volucella are laid and the 

 larvae reared inside the nests of various Hymenoptera, it has been ascertained that 

 the species which resemble humble-bees visit for the same purpose the nests of 

 wasps, to which the flies bear no particular resemblance. And it is hardly credible 

 that the wasps give access to the flies under the delusion that they are members 

 of the community, as was conceivable in the case of the bees. We arc compelled 

 therefore to conclude that the flies are allowed by the bees and wasps to come and go 

 without interference for some reason apart from the resemblance that exists between 

 the two sets of insects. It is, of course, possible that the similarity offered by the 

 flies to bees and wasps is more deeply seated than was supposed, and affects such 

 senses as touch or smell, or some other unknown sense, but there seems no evidence 

 to justify this supposition; and if the maggots of the flies feed on the larvae of the 

 bees or wasps, we are not yet in a position to offer an explanation of the pheno- 

 menon If they play the part of scavengers, clearing the hive of waste matter, the 

 reason for the admittance of the flies becomes clear, 



Closely resembling many of the Syrphidce in their banded coloration, 

 which imparts to them a wasp-like aspect, the members of the family Conopidce 

 may be recognised by the absence of the spurious vein in the wings, and also by 

 their broad heads, of which the fore-part is produced into a conspicuous promin- 

 ence bearing the long antennae. Like the horse-flies, the Conopida in the adult 

 stage frequent flowers, but they lay their eggs in the bodies of various Hymen- 

 optera, like bees and wasps, and also in crickets and other Orthoptera. Here 

 the eggs hatch and the larva' \'m\ upon the living tissues of their prey, and 

 here they undergo their metamorphosis, although they do not invariably 

 quit the 'place of their development upon the death of the victimised host. 

 Taschenberg, for example, found the pupa of Conops vittatus emerging from 

 the abdomen of a humble-bee which had been for six months in his collection. 

 The Conopidce are widely distributed, and especially abundant in the tropica 



