THE RESTING HABIT OF INSECTS, ETC. 3 



food enoniionsly in excess of that required for their ordinary needs, in 

 order to prepare them for the long fast which they have to undergo. 

 The ordinary natural cravings of hunger are not sufficient, one would 

 think, to account for this, inasmuch as such animals gorge themselves 

 beyond all possible bounds of repletion. Does heat or some other 

 cause act as the stimulus which causes this gluttony ? If so, it is 

 quite clear that this is an essential part of the complex system which 

 leads up to, and, in fact, permits of, successsful hybernation. Let us 

 see how far our knowledge of insects enables us to understand this 

 matter, and what facts entomology gives bearing on it. Among 

 butterflies and moths a great number of species hybernate in the imago 

 state. ]\Iany of these follow out the usual law of feeding ravenously 

 before their period of hybernation commences. We see thousands of 

 Gonepteryx rhainni, and of Vanessa to, feeding in the clover and 

 lucerne fields, or on the flowers that clothe our hedgesides during the 

 month of August ; but, hoAvever warm the weather, these disappear in 

 normal years before or by the time September appears, and, strange to 

 say, the finer and hotter the summer, the earlier do they disappear. 

 Again, Pyrameis atalanta may be seen until late autumn, whilst the 

 hops are yet in blossom, and afterwards, until the ivy sheds its bloom, 

 ravenously imbibing the nectar therefrom. Our hybernating moths, 

 too, are well-known as gluttons at ivy bloom, or any other available 

 sweets, before their winter fast begins. But among all our hybernating 

 species the most remarkable perhaps is Vanessa urticae. These butter- 

 flies emerge from the pupa? in June, and, after a day or two, in the 

 hottest season of the year, a part of almost every brood enters into 

 hybernation. Another part of the brood pairs, and eggs are laid, which 

 in August produce a new brood, that also in part goes into hybernation 

 almost at once, whilst again the other part attempts to perpetuate the 

 species. Natural forces, however, are against the progeny of the insects 

 comprising this latter part, natural forces in autumn and winter are too 

 strong for them, and they are killed off before they come to maturity. 

 It is clear, here, that hybernation is a preservative habit, enabling the 

 insect to escape from what would otherwise prove a sufficiently destruc- 

 tive influence to annihilate it, a condition of things which actually 

 occurs in our country in an allied species — Pyrameis cardui — which, 

 however, is often present in countries in which it has been again and 

 again annihilated, owing to its migrating tendencies. It is supposed by 

 many good naturalists, although without any very strong positive 

 proof, that a scarce race of this species has adopted hybernation, and 

 thus maintains its existence continually among us. 



But the known peculiarities of Vanessa urticae, and the almost 

 equally Avell-known cases of Vanessa io and Gonepteryx rhamni, lead 

 me to ask seriously whether "cold" is the external stimulus which, 

 acting on their peculiar organisation, causes the reaction of hybernation. 

 Like the marmot, a large number of our hybernating butterflies and 

 moths do go into hybernation on the approach of cold weather, but to link 

 these together because of this seems to be doing that against which the 

 learned Professor lifts up his voice, viz., assuming without proof that 

 this is the direct consequence of an external influence, simply because 

 the phenomenon and apparent cause occur side by side. Have Ave e\-er 

 yet proved a causal connexion betAveen cold and hybernation ? I do 

 not think so, Tavo phenomena may appear side by side, and may 



