ADAPTATIONS OF AQUATIC INSECTS 1 9 I 



devoid of insect life, the exceptions being a few chironomid 

 larvae which have been dredged in deep water, and fifteen 

 species of Halobates (belonging to the same family as our 

 familiar pond-skaters), which are found on warm smooth seas r 

 where they subsist on floating animal remains. 



Between ticle-marks may be found various beetles and col- 

 lembolans, which feed upon organic debris; as the tide rises, 

 the former retreat, but the latter commonly burrow in the sand 

 or under stones and become submerged, for example the com- 

 mon Anurida maritima. 



Insect Drift. Seaweed or other refuse cast upon the shore 

 harbors a great variety of insects, especially dipterous larvae, 

 staphylinid scavengers and predaceous Carabidae. On the 

 shores of inland ponds and lakes a similar assemblage of in- 

 sects may be found feeding for the most part on the remains 

 of plants or animals, or else on one another. During a strong 

 wind, the leeward shore- of a lake is an excellent collecting 

 ground, as many insects are driven against it. On the shores 

 of the Great Lakes insects are occasionally cast up in immense 

 numbers, forming a broad windrow, fifty or perhaps a hundred 

 miles long. Needham has described such an occurrence on 

 the west shore of Lake Michigan, following a gale from the 

 northeast. In this instance, a liter of the drift contained 

 nearly four thousand insects, of which 66 per cent, were crick- 

 ets (Nemobius), 20 per cent. Acridiidae, and the remainder 

 mostly beetles (Carabidae, Scarabaeidae, Chrysomelidae, Coc- 

 cinellidae, etc.), dragon flies, moths, butterflies (Anosia, 

 Pieris, etc.) and various Hemiptera, Hymenoptera and Dip- 

 tera. A large proportion of the insects were aquatic forms, 

 such as Hydrophilus, Cybister, Zaitha, and a species of caddis 

 fly ; these had doubtless been carried out by freshets, while the 

 butterflies and dragon flies had been borne out by a strong 

 wind from the northwest, after which all were driven back to 

 the coast by a northeast wind. While some of these insects 

 survived, notably Coccinellidae, Trichoptera, Asilidae, Acridi- 

 idae and Grylliclae, nearly all the rest were dead or dying, in- 



