THE AMERICAN ENTOMOLOGIST. 



may we hope from the birds ? Each can 

 answer this question for himself when he 

 learns ; ist, that the moths of every one of 

 the caterpillars mentioned above are noc- 

 turnal, adepts at concealment by day, and 

 exposed, while active, only to a few goat- 

 suckers and nocturnal birds of prey ; 2d, 

 that those caterpillars which develop under 

 the open sky are very hairy, and respected 

 by all birds except the cuckoo, and in 

 winter the charcoal titmouse {Af^sange 

 charbotmiere) ; 3d, that all the others, ex- 

 cepting Hadcna brassica, and this for a 

 few days only, live wholly concealed and 

 protected from depredation, or else en- 

 veloped in webs which birds do not like to 

 penetrate. Now what can a few cuckoos, 

 goat-suckers and titmice do against such an 

 innumerable population ? 



After this summary of incontestible facts, 

 the following recapitulation of principles 

 will stand some chance of being under- 

 stood : 



" I St. Birds are assembled in larger or 

 smaller troops only at the period of the 

 vernal and autumnal migrations, — that is 

 to say, when most insects are infinitely 

 less numerous than in midsummer. The 

 remainder of the time they live in pairs, 

 ordinarily scattered here and there, not 

 common in cultivated fields, while the in- 

 sects invade en masse the trees which they 

 attack, the products of the soil of which 

 they are the enemies. 



" 2d. Birds destroy enormous numbers 

 of insects, but these insects are in great 

 part innoxious, while some are eminently 

 useful. The species really noxious are so 

 few compared with the whole mass, that 

 birds are really of little service. They may 

 even injure us, — either by devouring our 

 fruit or by eating grain in seed time or in 

 harvest, but especially by killing so many 

 carnivorous or parasitic insects, which ren- 

 der us the greatest service. 



" 3d. Those insects which give us most 

 cause to complain are some of them large 

 enough to brave the birds, others (and 

 these are commonly the most formidable) 

 too small to attract their attention, and 

 still others offensive to the taste. Many 



are nocturnal and remain hidden by day, 

 with an instinct of self-preservation as well 

 developed as that of larger animals, or re- 

 maining motionless, are overlooked by 

 birds, which perceive much more easily 

 and pursue more willingly insects which 

 fly or run ; some live underground or in 

 houses, and all are endowed with a fe- 

 cundity which sometimes astonishes the 

 imagination, and which, at all events, is 

 such that man, with the most persevering 

 and assiduous diligence cannot extermi- 

 nate them even in a small field, cannot 

 even relieve his house of them, — no, not 

 so much as a single room. 



" 4th. The caterpillars and other larvas 

 which are especially injurious, nearly all 

 live hidden under the earth or bark, within 

 the wood, in the stems of plants, in fruits, 

 in habited places, or under silken webs, 

 and pay the birds only a slender tribute. 



'' Those which are exposed during their 

 growing period are generally covered with 

 hairs which repulse the birds ; some are 

 nocturnal, and disappear before day, and 

 others are protected by their excessive mi- 

 nuteness. 



"Who does not see that, hunting insects 

 without the least discernment, birds destroy, 

 among many harmless species, many 

 useful ones also, and especially parasites, 

 which, almost wholly diurnal and endowed 

 with great activity, are particularly liable 

 to become their prey ?" 



THE MIGRATIONS OF BUTTERFLIES. 



The fact that many animals, especially 

 rats, mice and lemmings, occasionally mi- 

 grate from place to place in immense 

 numbers is familiar, and abundantly re- 

 corded. These animals are not normally 

 migratory but become so only as a result 

 of excessive multipHcation, and the migrat- 

 ing habit, when once developed, possesses 

 some peculiarities not easy to explain, one 

 of which is that the movement is usually 

 very persistent in some given direction. 

 Many insects that usually exhibit no migra- 

 tory tendencies, likewise exceptionally con- 



