LOCAL DISTRIBUTION OF INSECTS. 513 



water. Lixus paraplecticus, Tanysphyrus Le?nn<z, Ba- 

 gous atrirostris, are of this description. A species of 

 Ceutorhynchus of Germar's third family (C. Natator K.) 

 swims well. On aquatic plants you must look for Helo- 

 des and the splendid Donacice, which, living on sub- 

 merged shoots and roots of these plants in their larva 

 state, continue to attend them when perfect. Amongst 

 the Eutrechma a , Elaphrus, Notiophilus, and Bembi- 

 dium frequent humid places, as the banks of rivers and 

 ponds ; and in such a station, under the roots of Poten- 

 tilla anserina, Polygonum, &c. if you should be fortunate 

 enough to find Omophron limbatum, which connects the 

 Eutrechma with the Eunechma, you will make a valuable 

 addition to the list of British insects. In the waters 

 also you will meet with many Heteropterous Hemiptera ,- 

 as Gerris, Hydrometra, and Velia, audallthe Hydrocorisa: 

 or water- bugs. On aquatic plants the larvae of some Le- 

 pidoptera feed, as Hydrocampa stratiotata, potamogata, 

 &c. Those also of the Trichoptera must be sought for 

 in the water : and if you should feel inclined to see an 

 interesting collection of their very curious cases, Mr. 

 Sheppard of Wrabness can gratify your curiosity. 

 Though few or no Hymenoptera frequent this element, 

 vast numbers of Dipt era are there alone to be met with 

 in their preparatory state, particularly the gnats. We 

 learn from Humboldt a curious fact with respect to those 

 of South America, or the Zancudos ,- that, with some ex- 

 ceptions, these pests do not frequent those rivers called 

 by the natives black waters, but only those which they 

 name white waters b . Of the Aptera, the genera Hy- 



a See above, p. 401. b Personal Narrat. E. T. v. 91, 



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