CIRCULAR-SEAMED FLIES 3025 



their prey by touch and not by sight, treat the drone flies with caution. Thus a 

 bluebottle fly placed in a web of the field spider was immediately and without hesi- 

 tation seized and devoured, although a bumblebee was avoided by the spider, which 



evidently fearing to come to close quarters let out a thread, and rushing round 

 and round its victim at a distance, succeeded in winding it up, and then approach- 

 ing, inflicted a bite which soon put an end to the insect's struggles. When a drone 

 fly was thrown into the web, the spider darted at it as before, but as soon as it 

 touched the fly with its fore-legs, recoiled, as if in alarm, then returning to the 

 attack dealt with the harmless victim just as it had previously acted with the hum- 

 blebee. The larvae of the drone flies live mainly in ditches and feed upon decaying 

 organic matter, and are 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 carcasses 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 honeybee. The belief that 

 honeybees are produced by spontaneous generation from carcasses of dead animals 

 has prevailed 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 carcasses of animals, that its larvae develop within the putre- 

 scent mass, and finally change into a sw 7 arm of flies, which in their shape, hairy 

 clothing, and color look exactly like bees, although they belong to a totally different 

 order of insects." Scarcely less interesting than the drone flies are the species of 



Volucella. These large flies (p. 3028, No. 9) mimic bumblebees in color and form, 

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

 the nests of bumblebees and lay their eggs among 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 bumblebees 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 are compelled therefore to conclude 

 that the flies are allowed by the bees and wasps to come and go without interfer- 

 ence 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 phenomenon. 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 Conspidce may be 

 190 



