33-2 IMPERFECT SOCIETIES OF INSECTS. 



rated, the majority — for instance, the lady-birds, saw-flies, dragon-flies, 

 ground-beetles, frog-hoppers, he, are not usually social insects, but seem 

 to congregate, like swallows, merely for the purpose of emigration. 

 What incites them to this is one of those mysteries of nature, which at 

 present we cannot penetrate. A scarcity of food urges the locusts to 

 shift their quarters, and too confined a space to accommodate their num- 

 bers occasions the bees to swarm ; but neither of these motives can 

 operate in causing unsocial insects to congregate. It is still more difficult 

 to account for the impulse that urges these creatures, with their filmy 

 wings and fragile form, to attempt to cross the ocean, and expose them- 

 selves, one would think, to inevitable destruction. Yet, though we are 

 unable to assign the cause of this singular instinct, some of the reasons 

 which induced the Creator to endow them with it may be conjectured. 

 This is clearly one of the modes by which their numbers are kept within 

 due limits, as, doubtless, the great majority of these adventurers perish in 

 the waters. Thus, also, a great supply of food is furnished to those fish 

 in the sea itself, which at other seasons ascend the rivers in search of 

 them ; and this probably is one of the means, if not the only one, to 

 which the numerous islands of this globe are indebted for their insect 

 population. Whether the insects I observed upon the beach, wetted by 

 the waves, had flown from our own shores, and falling into the water iiad 

 been brought back by the tide ; or whether they had succeeded in the 

 attempt to pass from the continent to us, by flying as far as they could, 

 and then falling had been brought by the waves, cannot certainly be ascer- 

 tained ; but Kalm's observation inclines me to the latter opinion. 



The next order of imperfect associations is that of those insects which 

 feed together : these are of two descriptions ; those that associate in their 

 Jirst or last state only, and those that associate in all their states. The 

 first of these associations is often very short-lived: a patch of eggs is 

 glued to a leaf; when hatched, the little larvae feed side by side very 

 amicably, and a pleasant sight it is to see the regularity with which this 

 work is often done, as if by word of command ; but when the leaf that 

 served for their cradle is consumed, their society is dissolved, and each 

 goes where he can to seek his own fortune, regardless of the fate or lot of 

 his brethren. Of this kind are the larva of the saw-fly of the gooseberry, 

 whose ravages I have recorded before, and that of the cabbage butterfly ; 

 the latter, however, keep longer together, and seldom wholly separate. 

 In their final state, I have noticed that the individuals of Thrips Phy^- 

 pus, the fly that causes us in hot weather such intolerable titillation, are 

 very fond of each other's company when they feed. Towards the latter 

 end of last July, walking through a wheat-field, I observed that all the 

 blossoms of Convolvulus arvensis, though very numerous, were interiorly 

 turned quite black by the infinite number of these insects, which were 

 coursing about within them. 



But the most interesting insects of this order are those which associate 

 in all their states. Two populous tribes, the great devastators of the 

 vegetable world, the one in warm and the other in cold climates, to which 

 I have already alluded under the head of emigration — you perceive I am 

 speaking of Aphides and Locusts — are the best examples of this order: 

 although, concerning the societies of the first, at present we can only say 



