THE THEREVID^. 87 



from the thorax, and less occupied by the eyes than in the Tabanidse. The head is bearded 

 at the sides and beneath. The antenna? show three joints, of which the third is usually simple 

 and long, and terminated by a bristle or style of two joints. The proboscis is generally of moderate 

 length, but strong, horny, and sharp-pointed ; it encloses three bristles (besides the labrum), and 

 the upper one, which probably represents the united mandibles, is very strong. The abdomen is 

 elongated, pointed, and generally composed of eight segments ; the tarsi have two pulvilli ; the 

 wings generally show two complete cells on the disc. 



In their habits the Asilidae are among the most predaceous of their order; but instead of feasting 

 upon the blood of the higher animals, they content themselves with sucking out the fluids of other 

 insects, which they pounce down upon with hawk-like violence, often lying in wait for a passing prey 

 upon fences, walls, and the twigs of trees. Their prey consists largely of Dipterous flies, but they 

 also freely attack insects of other orders ; even the hard coats of Beetles and Hymenoptera are not a 

 sufficient defence from the formidable lancets of the Asilidae, and the larger species of the family are 

 even said to attack and destroy Dragon Flies. 



The larvae are long, depressed, footless grubs, with a scaly head ; they live underground, 

 feeding upon the roots of plants and decaying vegetable matter, or in rotten wood ; they undergo 

 their transformations in the same situations, and the pupae have the head armed with spines, and 

 the segments of the abdomen with rows of spinules, which assist the insect in making its way out 

 when the time for its final change has come. 



The family probably includes about the same number of species as the preceding one, and 

 they are distributed over the whole surface of the globe. They are 

 generally robust, hairy insects, with strong limbs, and they hold 

 their prey with their fore legs while engaged in sucking out its 

 juices. Many of them, and especially the exotic forms belonging 

 to the genus Mydas, inhabiting the tropical parts of America, are 

 of large size ; Mydas yiganteiis, a deep black Brazilian species, often 

 measures an inch and three-quarters in length. Even of the 

 European and British species, one of the commonest, namely, the 

 Asilus crabroniformis, attains a length of an inch. It is of a tawny 

 yellow colour, with four brown stripes on the thorax, and the basal 

 part of the abdomen black. This insect is said sometimes to attack 

 cattle and other animals. Leptogaster cylindricus, a British species, ASILUS CRABRONIFORMIS. 



is remarkable for its slender cylindrical abdomen, which is con- 

 siderably longer than the wings, and in the female is slightly enlarged at the end. It has in 

 consequence some resemblance to the Tipulce, and, like those insects, frequents meadows during the 

 summer. 



FAMILY XL THEREVID^E. 



The Therevidte form a small family of insects, similar to the Asilidse in the general form of 

 the body, but distinguishable at once by the structure of the proboscis, which is short, not very 

 prominent, and terminated by fleshy lips. The bristles enclosed in it are also much feebler than 

 in the Asilidae. The antennae are short, of three joints, and the third joint has a thin style at 

 its extremity ; the ocelli are distinct ; the abdomen consists of eight segments ; the legs are thin, 

 and the tarsi have two pulvilli ; and the wings have one complete discoidal cell. The larvae live 

 in vegetable mould, or in rotten wood, and are exceedingly long and slender, having a small head 

 with a pair of short antennae, and apparently consisting of about twenty segments, owing to a 

 seeming division of the middle segments. The pupa has the fore part armed with spines, like 

 that of Asihis. The species, which are generally of modei'ate size, are found in most parts of 

 the world, and agree in their general habits with the Asilidse, although they are more sluggish 

 in their movements, and cannot display so much ferocity in the pursuit of prey. They feed chiefly 

 upon other Diptera, for which they lie in wait in various situations, sometimes on the ground 

 in sandy places, but more frequently upon the leaves and branches of shrubs and trees, and on flowers. 

 The commonest British species is Thereva plebeia, an insect rather more than one-third of an 



