HABITS OF TWO PARASITES OF BLOW-FIJES, 



221 



little chance of completing their developiueiit, and would probably 

 be killed by mites or some other enemy. 



Many attempts were made to observe the initial process of 

 making the exit-hole, but without success. However, on one 

 occasion a female was observed enlarging an exit-hole. A few 

 days previously this particular puparium had been enclosed in a 

 glass tube stopped with a cork. The tube was under observation 

 with the aid of table binoculars to watch the movements of some 

 adults of both sexes which had emerged. There were two exit- 

 holes in the puparium, dorsally, with centres about 3 mm. apart, 

 one being much larger than the other, and through the former 

 all the large females in the tube must necessarily have escaped. 

 Suddenly a female's antennae were noticed to issue from the small 

 exit-hole, and w^ei'e violently agitated. The upper part of the 

 epicranium could be seen against the inside of tlie pu})arium ; the 

 head was then moved, as was evident by the changing positions 

 of the waving antennae ; eventually, after the scajies had several 

 times come into contact with the serrated edges of the exit-hole, 

 they were withdrawn ; the female could then be seen changing 

 its position. This accomplished, the head began to appear latero- 

 ventraliy through the hole, the right eye coming up first; 

 gradually more and more of the head appeared still maintaining 

 its latero-ventral aspect, until the edge of puparium was slightly 

 oblique to the junction of the mandibles. The right eye and 

 gena were then above the suiface of the })uparium, the antennse 

 still inside. The female now began to bite the puparium, the 

 right mandil)le coming down on it from the outside, the left 

 working up on it from inside. This process continued in a leaf- 

 eating-caberpillar-like movt ment — semicircular foiwards and 

 backwards — until tlie hole was made large enough to enable the 

 female to escape. No effort was made to test the size of the 

 hole; the insect continued to bite until, suddenlv ceasing, it 

 began changing its position again until it was ventral side up 

 inside the puparium, then, moving forward an<l bending upwaicls, 

 the antennfe. head, anterior legs, thorax, middle and posterior 

 legs, and abdomen appeared successively, until the female was on 

 the surface of the puparium, erect. It immediately began clean- 

 ing itself : the apex of the al^domen bore a. portion of the pupal 

 exuvia, wdiich came awav with a minute white meconial discharge. 

 A few seconds later the female was found by a male. 



In the laboratory, when tlie puparia are unburied in soil, these 

 discharges can be seen scatteied all over them, aiul appear as 

 minute white strings. 



The Sexes. — Size : — The females ^ ary from 1"0 mm. to 2*30 mm., 

 the males from 0 60 mm. to 2'0 mm. (6). 



General appearance,. — Both sexes are distinguisliable to the 

 naked eye. The females have large wings extending beyond tlie 

 apex of the abdomen, whereas the ma.les (text- fig. 17) are semi- 

 apterous ; their rudimentary wino-s do not extend farther than 

 the third abdominal segment. 



