6 PEOCEEDINGS OF THE NATIONAL. MUSEUM. vol.64. 



simply finds the mouth of a burrow and crawls down into the nest- 

 ing cell of its host. Observations, however, indicate that this is not the 

 way entrance is effected. Repeated attempts to induce larvae reared 

 in the laboratory to enter the burrows known to be occupied by the 

 host invariably failed. If placed at the mouth of a burrow the larvae 

 refused to enter it ; if placed down on the walls of the burrow inside 

 it, they invariably scrambled out and wandered away. It- is our 

 conviction that the first instar succeeds in attaching itself to the 

 host, and when she enters the burrow rides down to the nesting cell 

 ujDon her. The mandibles of the parasite (fig. 13) are notched on the 

 inner margin, which fits them admirably for seizing and holding en 

 to the hair of the host, and if a bee is placed in a breeding jar among 

 active larvae every one that comes in contact with her will seize hold 

 of a hair or spine with the mandibles and hold on so tenaciously that 

 both bee and parasites can be killed in a cyanide bottle without the 

 parasites releasing their hold (fig. 24). Likewise, if a camel's-hair 

 brush is brought into contact with them they will seize the hairs 

 with their mandibles and hold on tightly so long as the brush is 

 moved vigorously about or rubbed against some object in an effort to 

 dislodge them. So soon, however, as the movement of the brush i« 

 stopped the larvae will release their hold and scramble off the brush. 

 If the brush is free of contact with another object the larva will 

 release its hold with the mandibles and crawl about over the brush ; 

 but if it is dislodge^ while moving about it can attach a thread to 

 the brush and thus let itself down bj^ spinning a thread as do tlic 

 larvae of many Lepidoptera. In this operation the larva goes down 

 head first. Wliat advantage the larva derives from this power to 

 spin a thread has not been learned. 



On May 20, 1920, males of Colletes i^fithorax were abundant 

 about the nesting site eagerly searching for the females, which on 

 that date were emerging freely. A number of both males and fe- 

 males was captured and killed in a cyanide bottle and, after being 

 taken to the laboratory and placed on pins, were examined for first 

 instars. Sixty per cent both of males and of females were found 

 infested, the different individuals carrying from one to four Tri- 

 crania larvae. On the males, all the larvae, with the exception of 

 one, were found clinging to hairs on the posterior, ventral part of 

 the head. On the females, however, although a few were found 

 adhering to hairs on the ventral parts of the thorax, the great ma- 

 jority of the larvae were clinging to hairs on the posterior, dorsal 

 part of the head or on the vertex. 



Beauregard, quoting from the researches of Fabre, writes that the 

 female of Sitai^s humeralis places her eggs in the entrance of the 

 burrow of the host {Antophora pilipes) and that the first larval 

 instars, which on hatching from the eggs find themselves at the open- 



