INDIRECT BENEFITS DERIVED FROM INSECTS. 279 



portunity of catching them 1 . 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 furnishing food to fishes and birds, beginning with 

 the former. 



Our rivers abound with Jish of various kinds, which at 

 particular seasons derive a principal part of their food 

 from insects, as the numerous species of the salmon and 

 carp genus. These chiefly prey upon the various kinds 

 of Phryganeee, 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 Ephemerae. 

 Besides these, the waters swarm with insects of every or- 

 der, as numerous in proportion 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 ak 

 most all. 



Reaumur has given us a very entertaining account 

 of the infinite hosts of Ephemeras that by myriads of mil- 

 lions emerge at a certain season ©f the year from some 

 of the rivers in France, which, as it is well 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 ha- 

 bitations, which they seldom quit ; or they swim about 

 and walk upon the bed of the stream, or conceal them- 

 selves under stones or upon pieces of stick. Though their 

 life, when they assume the perfect state, is usually ex- 



* St.. Pierre, Voy. 73. 



