288 INSECTS AND MAN 



they are deposited with their micropyles the points from 

 which the larvae escape downwards. As the mosquito 

 crawls over the leaves its abdomen comes in contact with 

 the bases of the eggs, which, for the time being, are, so to 

 speak, standing on their heads. The adhesive cement 

 causes the eggs to adhere to the ventral surface of the 

 mosquito's abdomen, and, in their new position, their 

 micropyles are at their free ends. Sooner or later the 

 mosquito will seek a meal of blood, human for choice, and 

 the minute Dermatobia larvae (fig. 84), escaping from their 

 eggs, will find a wound in the skin of their host, ready- 

 made for them to enter. The larval growth, of course, 

 takes place beneath the skin, and rapidly causes an angry 

 boil, which necessitates immediate surgical attention. If 

 left undisturbed, the larvae would possibly leave their host 

 to pupate, though this is merely conjecture, based on the 

 habits of other larvae with similar life-histories. 



In addition to Dermatobia, three other Diptera the 

 Tumbu fly and Congo flour maggot of Africa, and the screw- 

 worm fly of the New World are parasitic upon man. The 

 Tumbu fly, Cordylobia anthropophaga (fig. 87), which, in its 

 larval stage, is known as the Cayor maggot, is essentially 

 African. Both man and animals are attacked, the favourite 

 hosts being dogs, rabbits, and goats, which are usually 

 injured in the scrotum ; but whatever part of the body is 

 attacked, and whatever the host, the nature of the infesta- 

 tion is the same. The larva forms a considerable swelling 

 or boil beneath the skin, through the centre of which there 

 is an opening for breathing; when mature the host is 

 forsaken, and pupation takes place in the ground. Exactly 

 how the larva passes beneath the skin is unknown. By 

 some travellers it is thought that the fly oviposits in soil, 

 and that when the larvae hatch from the eggs they 

 penetrate the skin of people sleeping on the ground; by 

 others it is thought that the eggs are laid in clothing, so 

 that when they hatch the larvae find their food close at 



