DIPTERA. 71 



prepare an abundant supply of provision for their larvae as soon as 

 they are hatched. The following are the means they employ. It is 

 well known that certain fossorial Hymenoptera carry their prey 

 other insects which they have caught, weevils, flies, &c., and which 

 they intend should serve as food for their own larvae into their 

 subterranean abodes. These Diptera, spying a favourable moment, 

 slip furtively into their retreats, and deposit their eggs on the very 

 food which was intended for others. Their larvae, which are 

 soon hatched, make great havoc among the provisions gathered 

 together in the cave, and cause the legitimate proprietors to die 

 of starvation. 



" This instinct," says M. Macquart, " is accompanied by the 

 greatest agility, obstinacy, and audacity, which are necessary to carry 

 on this brigandage ; and, on the other hand, the Hymenoptera, 

 seized with fear, or stupefied, offer no resistance to their enemies, and 

 although they carry on a continual war against different insects, and 

 particularly against different Muscides, they never seize those of 

 whom they have so much to complain, and which, nevertheless, 

 have no arms to oppose them with." 



The Sarcophagtz are a very common family of Diptera, and are 

 chiefly to be found on flowers, from which they steal the juice. The 

 females do not lay eggs, but are viviparous. 



Reaumur, with his usual care, observed this remarkable instance 

 of viviparism proved in a fly, which seeks those parts of our houses 

 where meat is kept to deposit its larvae. This fly is grey, its legs are 

 black, and its eyes red. 



When one of them is taken and held between the fingers, there 

 may often be seen a small, oblong, whitish, cylindrical worm come 

 out of the posterior part of the body, and shake itself in order to 

 disengage itself thoroughly. It has no sooner freed itself than the 

 head of another begins to show. Thirty or forty sometimes come out 

 in this manner, and, on pressing the abdomen of the fly slightly, more 

 than eighty of these larvae may sometimes be made to come out in a 

 short space of time. If a piece of meat be put near these worms, 

 they quickly get into it, and eat greedily. They grow rapidly, 

 attaining their full size in a few days, and make a cocoon of their 

 skin, from which in a certain time the imago issues. If the body of 

 one of these ovoviviparous flies (for the eggs hatch within the parent) 

 be opened, a sort of thick ribbon of spiral form is soon seen. This 

 ribbon appears at first sight to be nothing but an assemblage of 

 worms, placed alongside of and parallel to one another; 



Each worm has a thin white membranous envelope, similar to 



