23 



b< ar spiracles. When it becomes full <ir()\vii the larva makes its 

 K>wn cocoon of earth and silk, united in such a way that the re- 



FiG. 13. — Gray horsefly (Tabanus cymatopliorus), 

 female, enlarged to one and a half diameters. 



sidt is a rather dense structure which appears as if moulded 

 from a poor grade of cement. The cocoon finished, the larva re- 

 mains in it unchanged for some length of time, just how long 

 1 have not been able to determine for several reasons. 



The cocoon varies in size to an extent that is quite notice- 

 :a,ble, and one is led to suspect that the smaller cocoons contain 

 the males and the larger ones the females. It was proven by 

 several observations that the nests which contained the small 

 cocoons had not received as large supplies of food as those con- 

 tjiining the large cocoons, and the smaller ones were noticeably 

 lighter in coloration. 



The adult is a conspicuous wasp more than an inch in 

 length, with a well-developed sting which she can use effectively 

 ij case she gets in a tight place, but she never attempts to pro- 

 tect her nesting site or her young by stinging the intruder, as 

 some wasps do. Both sexes are black in general coloration, with 

 the legs largely yellow, and small spots on the sides of the thorax 

 and larger spots on the abdomen greenish yellow. Several fe- 

 7nales may have nests in close proximity to one another, but each 

 attends to its own, and on this account the species is often re- 

 ferred to as a solitary wasp, as distinguished from the the hornets 

 and other wasps which form a group known as social wasps. The 

 nest is a simple burrow excavated in the soft sand by the fe- 

 jrnale herself, at least in cases observed, and in this burrow the 



