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 [ 
observed that a numerous brood of Aphides (not A. betule, 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 ofan 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 pupz 
in security from the too great cold of winter and the attacks of enemies, 
the larvee 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 
pupz’ has been plausibly assigned by Résel, 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 larvee were to be hatched before winter and to hybernate in that state, 
they would haye 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. f 
To the insects which hybernate in the /arva state, of course belong, in 
the first place, all those which exist under that form more than one year; 
as many Jelolonthe, Elateres, Cerambyces, Buprestes, and several species 
of Libellula, Ephemera, &c. There are also many larve, which though 
‘their term of life is not a year, being hatched from the egg in autumn, 
