552 THE BUTTERFLIES OF XEW ENGLAND. 



course. Even the portion which is concerned in it may be unequally 

 affected, some arousing from the torpor at the end of a few weeks and pro- 

 ceeding regularly thereafter Avith their transformations ; others continuing 

 torpid to and through the winter. This shows its direct relation to hiber- 

 nation. The same phenomenon occurs in the chrysalis state, where some- 

 times early in the season a portion of a brood will disclose the butterfly, 

 while another portion will retain the inmates until the succeeding spring. 

 But its occurrence in the active larval stage is far more unexpected. 



This lethargy in caterpillars Avas first observed by a French naturalist 

 named Vaudouer more than sixty years ago, but his statements lay a long- 

 while nearly unnoticed. According to this observer (a full account of 

 whose observations is given elsewhere), one of the European species of 

 Brenthis upon which he experimented flies in May and again in July and 

 August. The caterpillars from the second summer brood are half grown 

 when winter comes, hibernate in this stage and in time produce the spring 

 brood ; the caterpillars of the spring brood, when they have reached the 

 hibernating age, late in June, act in a precisely similar manner, and some 

 of them do not arouse until the succeeding spring, when, with the cater- 

 pillars of the summer brood, they produce a new spring brood ; but other 

 caterpillars of the spring brood, which became lethargic, awaken from 

 their torpidity after a time, resume eating, undergo their transformations, 

 and emerge as butterflies in July and August. 



This same feature occurs in some of our own species of Brenthis as I 

 have several times observed. It is also found in some of the Melitaeidi, and 

 I suspect also in the genus Argynnis from the fact that there are in some 

 places two apparent broods of the butterfly, months apart, but only one 

 period of egg-laying. Since in these cases the winter is passed in the 

 larval condition, the caterpillar just from the egg, it would appear proba- 

 ble that lethargy makes its appearance in the spring and early summer 

 among the growing caterpillars, or else, what seems less likely, the period 

 passed in chrysalis is very unequal . 



It is possible that to this list should be added those Theclidi and Chry- 

 sophanidi which ostensibly pass the winter in the egg state. If, as is 

 probable, these eggs mature during the hot season in which they are laid, 

 and not in the succeeding, cooler, early spring when the caterpillar 

 escapes, then the only difterence between these caterpillars and those of 

 the Argynnidi is that one passes the winter within, the other without the 

 egg-shell ; and their refusal to escape in the warm weather points to pre- 

 mature hibernation, beginning in a kind of lethargy. 



The cause of this strange feature in butterfly life must be attributed, like 

 all other points in their history, to the struggle for the perpetuity of the 

 species. Should disaster befall the advance guard who have not halted by 

 the way, the sluggards can take up the work ; the chances of surviAal are. 



