Abstract
1) Observations and colletions of swarms of Culex pipiens pallens were made from May through November, 1950 at Sinmei town, Fukui prefecture. 2) The percentage number of female against male in the swarming population is somewhat variable according with the season, but as a whole, the value was about one percent. This suggests that in the course of evening swarm of this mosquito species, one female against 100 males will be always found without regard to the place, time and season. 3) The males of this species continue the swarm formation during a period of one month or more after the females ceases from entering house or cow-shed to feed, showing that the swarming habit survives the feeding habit at low temperatures below 15℃. in average for month. The last female in a swarm was obtained as late as on 24th November. 4) The starting time of swarming is at 15-10 Lux in mid Summer but in mid October it is at 500 Lux or above and in the last part of the month it is at about 1200 Lux and finally in late November it is at about 1700 Lux, showing that the time progressively getting fast mainly with the days becoming short and partly with the decrease in temperature when it is below 20℃. or so. 5) 285 individuals (243♀ and 42♂) belonging to eight species were found mingling within the swarm of this species, of which C. tritaeniorhynchus was the most numerous. It is strange that the total number (197) of the female mosquito of the above species by far precedes that (110) of the female of C. pipiens pallens itself. 6) Considerations on the functions of swarming and on the factors governing swarm formation were made.
