44 ANIMAL BIOLOGY 



The family Tabanidae, including horse flies, green heads 

 and their allies, is formed mainly of blood suckers which 

 pierce the skin with the sharp stylets of their proboscis. 

 The larvae generally live in the water or in damp situations; 

 this is why the flies themselves are usually more abundant 

 in low swampy regions. 



Few of the Diptera are more annoying than the small, 

 fiercely biting, black flies or buffalo gnats (Simulium) 

 which occur in such numbers in certain parts 01 the 

 United States and especially in Canada, as to make life 

 almost intolerable at times for man 

 and beast alike. The larvae inhabit 

 running water, attaching them- 

 selves to rocks and other objects by 

 the posterior end of the body. 



A large family of the Diptera, the 

 Tachinidae, make their living during 

 their larval state as parasites with- 

 FIG. 34. Black gadfly m the bodies of other insects. The 

 enlarged. (After female fastens her eggs upon the 

 skin of some insect and when the 



young grubs are hatched they bore into the body of their 

 victim and proceed to devour its internal organs. In 

 general the Tachinidae deserve our gratitude because they 

 afford a means of holding in check the ravages of de- 

 structive caterpillars, grasshoppers and other injurious 

 insects. 



Other scourges of the insect world are the robber flies, 

 Asilidae, which swoop down upon their prey, carrying it 

 off and sucking its blood. We can no more than mention 

 the hover flies, Syrphidae, that have the curious habit of 

 hovering over one spot during the summer days ; the fuzzy 

 bee flies, Bombyliidae, that are often mistaken for bees; 

 the long-legged, awkward crane flies, Tipulidae; the beauti- 



