6o 



INSECTS. 



proboscis, and prey upon insects of various kinds, often seizing and carrying oft' 



butterflies, much larger than themselves. The general form of the members of 



this family is shown in Fig. 1 of the annexed illustration, representing Dioctria 



oelandica, a species from the island of Oeland, off the coast of Sweden, with 



a shining black body, and wings of the same colour. Many species of the genus 



Asilus are found in Britain, but the largest and handsomest of all is the hornet 



robber-fly (A. crabroniformis), measuring upwards of an inch in length, and of a 



yellowish colour variegated with black, there being four stripes of the latter colour 



upon the thorax, and a broad transverse band across the base of the abdomen. 



Some of the tropical members of the family are far larger, those belonging to the 



genus Mydas, from South America, being scarcely surpassed in dimensions by any 



member of the order. The fly represented in 2 of the illustration is the tesselated 



empis (Empis tessellata), belonging to the family Empidai, the species of which 



are predaceous like the Asilidce, 



and resemble them in form, but 



differ in certain structural details 



which need not be dwelt upon. 



The tesselated empis — the 



largest member of the group 



found in Britain — is ashy grey 



in colour, and has its abdomen 



ornamented with a chess-board 



pattern. As Dallas expressed 



it, " when paired, the females of 



this and of many other of the larger species of the family are always found to 



be busily engaged in sucking out the juices of some other insect. It seems 



probable that the male seizes the opportunity of his intended partner being thus 



occupied to make his advances ; if her mouth were free he would in all likelihood 



himself fall a sacrifice to her voracity." 



The families of short-horned, straight -seamed flies hitherto 

 Bee-Flies 



considered resemble each other in the fact that the larvae live in the 



earth, and feed upon the roots of grass or other vegetable matter, while the adults 

 prey upon other animals, whose blood they suck. But in the bee-flies (Bomby- 

 liidce) — so called from the likeness in hairiness and shape they present to humble- 

 bees — the larvae, so far as known, live parasitically on other insects, attacking 

 grasshoppers, caterpillars, etc., while the adults suck the juices of flowers. The 

 genus Bombylius is represented in England by a small number of species, although 

 in the tropics there are large numbers of forms. In all the thick, fat body is 

 covered with long yellow hairs. The wings are powerful ; and the head is furnished 

 with a long proboscis, which is thrust into blossoms while the insect (No. 8 on p. 65) 

 stays poised in mid-air, like a hawk-moth when similarly occupied. The black-and- 

 white bee-fly (Anthrax semiatra) is mostly of a black tint, and clothed with hair 

 of the same colour ; but the hairs on the front part of the thorax and abdomen take 

 a yellowish tinge, the wings, as shown in the illustration, being black in the basal 

 half but clear elsewhere. These insects may be seen on the wing in dry, sunny 

 spots, stopping from time to time to suck a flower, or rest upon a stone, and seeking 



ROBBER-FLIES. 



1, Dioctria oelandica ; 2, Empis tessellata (nat. size). 



