552 HYBERNATION OF INSECTS. 



in spring of eggs deposited before winter, and of the leafing of the trees 

 upon which they have been fixed, and on whose foHage the larvae are to 

 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 unac- 

 quainted, 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. betulce, 

 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 admiration, 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 organization. 



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 pupae 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 situation. 

 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 mate- 

 rials, 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 Rosel, 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 neighborhood of their appropriate 

 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. 



