welch] water IXSECTS 221 



The Insect Life of Pond and Stream 



Paul S. Welch. 



University of Illinois. 



Part III. 



How THE Common Aquatic Insects Pass the Winter. 



Aquatic insects, as well as terrestrial insects, must have 

 means of providing against the hardships of our winters.' There 

 are two factors which are characteristic of this unfavorable season 

 and which threaten the lives of insects unless adequate adjust- 

 ment is secured. These factors are (1) the low temperature, 

 and (2) the scarcity of food, this factor being largely the result 

 of the first. This means that in order to successfully combat 

 these conditions the insect must have an inactive, resistant, more 

 or less protected stage which normally occurs at this sea- 

 son. This stage may be any one of the four life history 

 stages — egg, larva, pupa, adult. The majority of the common 

 aquatic insects which have been described in these papers pass 

 the winter either as Adults or as Larvae. The following partial 

 list will give some idea of the different hibernating stages: 



(1). Insects Which Pass the Winter as Adults. — Back- 

 swimmers, Waterboatmen. Smaller Giant Water Bugs. Larger 

 Giant Water Bugs, and the Whirligig Beetles burrow into the 

 mud in the bottom of the streams and ponds. Water Scavenger 

 Beetles and Diving Beetles burrow in the mud of the bottom or 

 in the mud of the banks and sides of the pools. The Marsh 

 Treader hibernates under the rubbish along the banks. The 

 Water Scorpion burrows into the mud of some sheltered bank. 

 Mosquitoes hibernate under boards, trash, and rubbish although 

 it is said that they may also pass the winter as larvae and are 

 sometimes found frozen in the ice but become active when thawed 

 out. The Water Strider passes the winter in the mud. under 

 leaves or rubbish on the banks, or at the bottom of the pools. 



(2). Insects Which Pass the Winter in the Pupal Stage. — 

 Of the common water insects, only some of the May Flies pass 

 the winter in this stage. 



f3). Insects Which Pass the Winter in the Larval or 

 Nymph Stage. — Damsel Flies, Dragon Flies, Blood Worms, and 

 Dobson Flies pass the winter in this stage in the bottoms of 

 streams and pools. Some of the May Flies and some of the 

 Stone Flies pass the cold season in the same way. Some of the 



