How insects behave 



Fig. 58. Diagram of a 'reflex arc', by which a muscle reacts automatically 

 to a sensory stimulus: s.o. is the sense organ in the skin, or integument (0; 

 the sensory neurone {s.c.) sends an impulse along the sensory nerve fibre 

 (5. fi.) to the association cell (a.c.)j which passes the impulse to the 

 motor cell (m.c.)', finally the motor nerve fibre (m.fi.) carries the signal to 

 activate the muscle (m). From Imms, 1957 



forests of Africa, and in the dense forest the larvae of the fly live in 

 shallow streams, among mud and decaying vegetation. When the adult 

 fly emerges from the pupa it disappears from the breeding-site, and is 

 to be found in the high forest canopy, 80-100 ft. up in the trees. Most 

 of the species feed there at night on monkeys, but one species feeds by 

 day on humans moving about in clearings, near villages, and around 

 their fires. After the fly has fed on blood its eggs ripen, and then the fly 

 returns, not to the tree-tops, but to the stream again, to lay eggs, con- 

 cealing them so well that in spite of prolonged study, only once or twice 

 have they been found. Yet the eggs must be there, since larvae are 

 plentiful. 



Unless we are prepared to assume that the fly has an intelligent 

 understanding of what it is trying to do, we have to believe that at 

 different times of its adult life it is governed by quite different patterns 

 of instinctive behaviour. 



Thorpe (1948) gives another example, the fly Stomoxys ochrosoma, also 

 in Africa, which flies over columns of the army ant, and drops its (the 

 fly's) larva in front of one of the worker ants that is returning empty- 

 handed to the nest. It is believed that the ant obediently carries the larva 



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