1 62 ENTOMOLOGICAL NEWS [June, '20 



wingless Tipulid or snow-fly, Chionea alpina Bezzi, an insect 

 which habitually lives on the snow, the species in question 

 in the high mountains of Switzerland. If Chionea was kept 

 in a glass tray, about one and one-half feet long, and covered 

 with wire netting and with two glass-plates in such a way 

 that the middle portion, at least one third of the whole length, 

 was covered only by wire netting, the two ends in addition 

 by the glass plates, and if the cage was oriented so that one 

 end of the trough was directed towards the open air (of a 

 porch) at about freezing temperature, the other end towards 

 the heated room, the insect would come to rest at the under- 

 side of the free portion of the ware netting and at the ex- 

 treme border of this free portion in the direction of the open 

 air. Inasfar as it refused to go under the glass plate, positive 

 phototropism (heliotropism) seemed to be excluded. If 

 the cage was turned i8o° the insect assumed the correspond- 

 ing position on the other side of the tray. In addition, it 

 could be observed that Chionea avoided the approaching 

 finger at some distance, and that this effect could be increased 

 if the hand was heated by means of an electric light bulb. 

 In this case, the insect could be driven, by merely approach- 

 ing it with the hand, under the glass-plate-covered portion 

 of the tray. The negative thermotropism seemed stronger 

 in the light than in the shade. If the animal was running 

 over the snow, approaching it with the finger was sufficient 

 to cause it to change its course but in this case an optic re- 

 action is not excluded. 



More characteristic cases of thermotropism are found among 

 mosquitoes. Concerning mosquitoes, Howlett (1910) was 

 the first to observe a positive thermotropism as underlying 

 the biting instinct. This observer carried out a series of pre- 

 liminary experiments and found that shed blood or human 

 sweat did not attract the females of Culex fatigans or Stegomyia 

 scutellaris any more than water. On experimenting with the 

 effects of heat, however, it was at once found that the fe- 

 males of Stegomyia scutellaris were readily attracted by the 

 hot air radiating from a test-tube containing hot water; the 

 male mosquitoes, on the contrary, paid no attention to it. 



