STREPS1PTEKA 3 



the abdominal segments of the host, with the oral or ventral surface upwards. Mouth parts vesl 

 Eves lacking. Thorax separated ventral ly from the head by the opening of the brood-canal, an inter - 

 membranal conduit between the pupal and adult skins leading from the unpaired median genital 

 apertures on the second to fifth segments anteriad to this ventral slit. 



Reproduction prolific, larviparous. Development endoparasitic and highlv hvpermetamorphic. 

 Hosts various, hexapodal. First larvae, or triungulinids, campodeiform hexapods. Parasitic stages 

 apodous. The male puparium, with cephalothorax protruded from the abdomen of the host, is merelv 

 the last larval skin with a cap-like lid, or cephalotheca. The pupa is similar to those of the Coleoptera 

 and Hvmenoptera and lies free in its case. 



Habits and metamorphosis. — Probably no order of insects has as a whole a more wonderful 

 or more interesting manner of life than the order which we are now studying. Only three orders of 

 insects have been constructed to contain parasites only, viz. : Siphunculata, Siphonaptera and Strepsi- 

 ptera, but parasitism has in the Strepsiptera reached a more complex development than is displayed 

 elsewhere among insects. 



The difference between the sexes is very striking. The male is an agile two-winged insect of 

 very small size, almost constantly on the wing. The female is merely a white legless sack with the head 

 and thorax flattened into a brown acariform disc. The abdomen remains permanently enclosed in the 

 body of the host and only the cephalothorax protrudes. The female's abdomen is merely a great sack 

 full of eggs, all of which develop at the same time, and not in ovaries, but free in the body cavity. The 

 real female never sheds its last skin. It has lost all instinct, except that which causes it to force its 

 chitinized cephalothorax out through the abdomen of its host. 



The eggs mature within the bodv cavitv and the young, which are numbered in the thousands, 

 find exit from the body of the parent through genital canals opening outside of the body. The}- find 

 themselves then in a larger passage formed between the venter of the female and its uncast pupal skin, 

 in which they pass forward and find exit through a slit between the head and prothorax on the cephalo- 

 thorax. The female reposes with its venter upward, so, when the young emerge, they crawl all over the 

 body of the host. These young are very lively little hexapods, which we call triungulinids. 



The triungulinid remains upon the body of the host until it gets a chance to slip off or is brushed 

 off into a nest or flower. In the latter case it waits until another host comes along and takes passage 

 with it. and is carried to a nest finally. When it reaches a nest it hunts around until it finds a larval 

 host, into which it quick]}' burrows. 



Inside its host parasitic life quickly causes it to lose its legs, and the eyes to disappear, and it is 

 soon entirely grub-like; then the segments of the head and thorax fuse. The male and female, 

 after the second molt, appear different, the female becoming as just described, while the male becomes 

 cylindrical and in the later stages shows a patch of eyes, resembling the primitive collembolan eye 

 patches, but more regular. The anterior portion hardens and is pushed outward, resembling a dipteran 

 pupa case, with tuberculate head and a little cap at the tip of the cylinder. Within this skin a real pupa 

 forms and finally the adult emerges by casting off the puparium-cap, or cephalotheca. The adult male 

 is a most peculiar insect with one pair of large, milky-white wings, shaped as a quadrant of a circle: with 

 a short transverse head; with large eyes composed of many separate facets divided by hairy partitions: 

 with antennae branched and covered with delicate sense organs; with rudimentary mouth parts, and 

 with paddle shaped balancers on the mesothorax. 



These insects fly like a flash, darting here and there, and with the balancers vibrating in unison 

 with the wings and making quite a loud hum for such tiny creatures. Their sole purpose in life is to 

 fertilize the females, which act is accomplished bv setting loose the semina in the brood canal or 

 T-sophagus of the female. 



