66 ANIMAL AGGREGATIONS 



Mosquitoes and midges. — Culicidae and Chironomidae form swarms 

 of males which maintain position as groups, although the individuals 

 within the swarm are continually darting from one part of the swarm 

 to another. Such swarms have been known for years, although their 

 significance has not been generally understood. Knab (1906) cites 

 his own observations on the swarming of mosquitoes and reviews the 

 literature to show that the swarms are composed of males which 

 hover over or near prominent objects such as trees, corn shocks, 

 house gables, or people. Enormous numbers of these dipterans may 

 be present in the collections, which occur generally in the early 

 evening of quiet and almost windless days. Straight-flying females 

 dart into these irregularly gyrating swarms of males and emerge in 

 copula with one male. One such newly mated pair was observed to 

 emerge from one swarm only to enter accidentally another near-by. 

 The copulating pair appeared to be greatly stimulated and flew into 

 the open as soon as possible. The swarming males which were as- 

 sociated for even so short a time with the mated pair also increased 

 their rate of flying and "danced up and down at a furious pace for 

 some time" before again quieting down to their normal rate of 

 gyration. With growing darkness the activity of the swarms in- 

 creased, but fewer successful matings took place; the entering female 

 would be set upon by two or three males, and all would fall together 

 to the ground, where they would separate. Later, females ceased 

 entering the swarms, and the males gradually dispersed. Counted 

 sex ratios of Culex were 897 males to 4 females (Knab), and of Chi- 

 ronomus 4,300 males to 22 females (Taylor, 1900). Mosier and Sny- 

 der (1919a) interpret the large morning swarms of tabanid flies which 

 they observed in the Florida Everglades as aggregations of males to 

 which females are attracted and into which they dart for the purpose 

 of mating. 



Frogs. — With the approach of spring frogs desert their hibernation 

 quarters for breeding places in the shallow ponds (Cummins, 1920). 

 Many hibernate in the mud at the bottom of these same ponds; but 

 others winter elsewhere, perhaps in nearby bodies of water or on 

 land among masses of dead vegetation, or in localities similarly 

 favorable. Cummins suggests that such frogs may migrate to open 



