518 HYBERNATION OF INSECTS. 



feed ; which two events, requiring exactly the same temperature, are always 

 simultaneous. Of this fact I had a striking exemplification in the spring 

 of 1816. On the 20th of February, observing the twigs of the birches in 

 the Hull Botanic Garden to be thickly set, especially about the buds, with 

 minute oval black eggs of some insect with which I was unacquainted, I 

 brought home a small branch, and set it in a jar of water in my study, in 

 which is a fire daily, to watch their exclusion. On the 28th of March I 

 observed that a numerous brood of Aphides (not A. betul<s y as the wings 

 were without the dark bands of that species) had been hatched from them, 

 and that two or three of the lower buds had expanded into leaves, upon 

 the sap of which they were greedily feasting. This was full a month before 

 either a leaf of the birch appeared, or the egg of an Aphis was disclosed in 

 the open air. To view the relation of which I am speaking with due admi- 

 ration, you must bear in mind the extremely different periods at which 

 many trees acquire their leaves, and the consequent difference demanded 

 in the constitution of the eggs which hybernate upon dissimilar species, to 

 ensure their exclusion, though acted upon by the same temperature, earlier 

 or later, according to the early or late foliation of these species. There is 

 no visible difference between the conformation of the eggs of the Aphis of 

 the birch and those of the Aphis of the ash : yet in the same exposure those 

 of the former shall be hatched, simultaneously with the expansion of the 

 leaves, nearly a month earlier than those of the latter ; thus demonstrably 

 proving that the hybernation of these eggs is not accidental, but has been 

 specially ordained by the Author of nature, who has conferred on those of 

 each species a peculiar and appropriate organisation. 



A much greater number of insects pass the winter in the pupa than in 

 the egg state ; probably nine-tenths of the extensive order Lepidoptera, 

 many in Hymenoptera, and several in other orders. In placing these pupa? 

 in security from the too great cold of winter and the attacks of enemies, 

 the larvae from which they are to be metamorphosed exhibit an anxiety 

 and ingenuity evidently imparted to them for this express design. A few 

 are suspended without any covering, though usually in a sheltered situa- 

 tion. But by far the larger number are concealed under leaves, in the 

 crevices or in the trunk of trees, &c., or inclosed in cocoons of silk or 

 other materials, and often buried deep under ground out of the reach of 

 frost. One reason why so many lepidopterous insects pass the winter as 

 pupae has been plausibly assigned by Ro'sel, in remarking that this is the 

 case with all the numerous species which feed on annual plants. As these 

 have no local habitation, dying one year and springing up from seed in 

 another quarter the next, it is obvious that eggs deposited upon them in 

 autumn would have no chance of escaping destruction ; and that even if 

 the larvae were to be hatched before winter and to hybernate in that state, 

 they would have no certainty of being in the neighbourhood of their ap- 

 propriate food the next spring. By wintering in the pupa state, these 

 accidents are effectually provided against. The perfect insect is not ready 

 to break forth until the food of the young, which are to proceed from its 

 eggs, is sprung up. 



To the insects which hybernate in the larva state, of course belong, in 

 the first place, all those which exist under that form more than one year ; 

 as many Melolonthce, Elateres, Cerambyces, Buprestes, and several species 

 of LibeUula^ Ephemera, &c. There are also many larvae, which though 

 their term of life is not a year, being hatched from the egg in autumn. 



