INDIRECT BENEFITS DERIVED FROM INSECTS. 281 



many reptiles : the tortoise ; frogs and toads ; and lizards 

 too of diiFerent kinds. St. Pierre nientions a small and 

 Aery liandso;iie species in the island oi Mauritius, that 

 pursues them into the houses, climbs up the wails, and 

 even %valks over glass, watching with great patience for 

 an opportunity of catching them'^. The common snake 

 also is said to receive part of its nutriment from them. 

 But to revert to insects as indirectly advantageous to 

 us, by furnisbitig food to fishes and birds, beginning with 

 the former. 



Our rivers abound ^vith Jish of various kinds, which 

 at particular seasons derive a principal part of their 

 food from insects, as the numerous species of the sal- 

 mon and carp genus. These chiefly prey upon the va- 

 rious kinds of Phryganeae, in their larva state called 

 case or caddis-worms ; and in their imago may-flies 

 (though this last denomination properly belongs only 

 to the Sialis lutaria^ which generally appears in that 

 month,) and Ephemers. Besides these, the waters 

 sv.arai with insects of every order, as numerous in pro- 

 portion to the space they inhabit, as those that fill the 

 air, which form the sole nutriment of multitudes of our 

 fish, and the partial support of almost all. 



Reaumur has given us a very entertaining account 

 of the infinite hosts of Ephemerze that by myriads of 

 millions emerge at a certain season of the year from 

 Honie of the rivers in France, which, as it is v. ell worth 

 your attention, I shall abridge for you. 



These insects in their first and intermediate state are 

 aquatic: they either live in holes in the banks of rivers 

 or brooks below the water, so that it enters into their 

 habitations, which they seldom quit; or they swira 



* SI. Pierre, Voij. 73, 



