TWO-WINGED FLIES AND FLEAS 97 



feed on dead animal matter, and a few prey on aphides 

 and mites. 



The family Bibionida includes stoutly-built flies, 

 with relatively short antennae. The eyes are excep- 

 tionally large, especially in the males. The sexes 

 differ remarkably in colour, the females being usually 

 red or yellow, the males deep black. The larvae feed 

 on the roots of grass and other plants, or in decaying 

 vegetable matter. In spring or early summer the 

 perfect flies may often be seen in enormous numbers 

 among the herbage in meadows and open places. 



The so-called sand-midges 1 are small black or 

 greyish flies, of which there are about a dozen British 

 species. They are chiefly remarkable for their blood- 

 sucking habits, and the annoyance which they cause 

 to man and beast. The early stages of the life- 

 history are passed in running water, where the larvae 

 feed on minute vegetable organisms, such as algae or 

 diatoms. 



The true midges 2 are for the most part harmless, 

 but certain species of the genus Cemtopogon are 

 inveterate blood-suckers, and are chief among the 

 pests that haunt our gardens in the summer twilight. 

 In this family, also, metamorphosis is usually accom- 

 plished in the water, or in damp situations. The 

 form of the larvae and their habits are very varied. 

 Some species, known as " blood-worms," live in mud 

 at the bottom of stagnant or dirty water. They are 

 especially interesting because their red colour is due 

 to the presence in their bodies of haemoglobin the 

 same oxygen-attracting substance that gives colour to 

 our own blood. 



The family Culicidcz comprises the gnats or mos- 



1 Simulida. 2 Chironomidce. 



7 



