THE GREGARIOUS HABIT IN BUTTERFLY LARV.E. 23 



in time of storm and stress. The trouble that fullgrown larvae of A. 

 crataegi have to maintain a footing on a smooth surface, on which a 

 silk holding has not been previously spun, is very marked, in fact, 

 they appear scarcely to be able to maintain their footing at all apart 

 from the silk. 



That the gregarious habit is useful, in that the nests of some 

 species form a safe retreat when not feeding, e.g., in the case of Aporia 

 crataegi, the Melitaeid species, young larvae of Aglais urticae, etc., 

 appears to be certain, from the manner in which they retire and form 

 little close companies within their web at such times, and, thus hidden, 

 remain motionless in the presence of danger. It would appear that 

 Eucheira carries this side of the value of gregariousness to its extreme 

 possibilities. 



That the web also forms an excellent protection at moulting-time is 

 certain, for at such times, the larvae retire within the web, and remain 

 together till the critical operation is over. This is the case, not only 

 in Aglais urticae, Vanessa io, Melitaea aurinia, and many other species, 

 but has also been noted in Aglais milberti, Euphydryas phaeton, and 

 many of the allied American species. 



The fact that the nests make an adequate hybernaculum in many 

 species, e.g., Aporia [crataegi), Melitaea (aurinia, cinxia, etc.), is 

 possibly due to the fact that the larvae have discovered that their 

 natural hiding-places by night form, most effectively, in winter, not 

 only a protection from wet and cold, but also a place of safety against 

 wind and flood, removing them well away from the foodplant, from 

 the surface of the ground, etc., and also as affording protection from 

 enemies, such as birds, etc., that hunt so assiduously throughout 

 the winter. Our previous description (antea, pp. 15-16) of the hyber- 

 naculum of Euphydryas phaeton illustrates this particular phase of 

 the value of gregariousness. 



There can be little doubt that gregariousness is also available as a 

 means of accumulated protection in making warning movements, at least 

 in the tree-feeding species, especially in those that maintain the gregarious 

 habits until the end of larval life, and, in this respect, considerable weight 

 must be given to the combined movements observable in most Vanessid 

 larvae, etc., when disturbed, and already noticed (antea, p. 19) in 

 those of Aglais milberti (antea, p. 20), in Euvanessa antiopa, as well 

 as in our British Melitaeids and the American Cinclidia harrisii, etc. 

 In the Vanessid larvae, it has been repeatedly observed that, when 

 annoyed or alarmed, every larva raises its head in just the same way, 

 and all make a simultaneous movement, at the same time exuding a 

 drop of fluid from the mouth, if the irritation be severe enough. A 

 solitary larva would not produce any definite effect in time to preserve 

 it from fatal injury, even though by that time its enemy discovered ifc 

 was distasteful ; whilst, in the mass, not only is the movement more 

 remarkable, and thus likely to be more effective, but the accumulative 

 secretion makes the distastefulness much more apparent. 



One may ask why, among the fritillaries, Melitaeas require a web, 

 whilst the Argynnids want nothing. One may ask in return, why the 

 individual larvae of the former move slowly or fall to the ground if 

 disturbed or handled, whilst the latter run at a tremendous pace to 

 find a hiding-place. We only know that nearly all objects are attained 

 in very different ways by different, but often allied, species, and why 



