22 



BRITISH BUTTERFLIES. 



bearing tubercles, one tubercle to a segment in each row, and one row 

 often more conspicuous than the others ; sometimes the entire body 

 bristles with these appendages. 



As has already been noticed, there is, in certain of our British' butterfly 

 larvae — Urbicolid, Pierid, Satyrid,etc. — a tendency to the obsolescence of 

 the primary setae. In other cases, however, the bases of the tubercles 

 are developed into long fleshy processes, carrying aborted setae, e.g., in 

 Vanessid, Argynnid, Melitaeid larvae, etc. That these complex processes, 

 often bearing long sharp spines, are modifications of the tubercular 

 structure, and are dermal appendages, appears certain if we examine 

 the newly-cast skin of a Vanessid or Argynnid larva. The structure of 

 the spines of the larva of Dry as jjaphia, the movable prothoracic horns 

 of Apatura iris, with moving tubercular bosses, and the anterior flexible 

 filaments constantly in motion backwards and forwards (especially 

 when eating or alarmed), are all important from the point of view of 

 the development of special external structures for protective purposes. 



The larvae of butterflies have then undergone special development 

 along various lines for protective purposes. The resemblance of some, 

 especially grass-feeding larvae, to their foodplants, makes them readily 

 overlooked; those of the Melitaeids closely resemble the long bloom-heads 

 of plantain and allied plants to which some species are attached, whilst 

 those of the Apaturids and others are most difficult to detect owing to 

 their resemblance to the leaves, etc., of their foodplant. Others, again, 

 are protected by the sharp, prickly spines into which the tubercles are 

 modified, e.g., the Vanessids, whilst others again have bright warning 

 colours, or are protected by nutant spines, etc., evaginable osmateria, 

 e.g., the larvae of the Papilionids. Butterfly larvae, therefore, show 

 considerable variety in their means of defence and consequent 

 ability to escape their vertebrate enemies. They are, however, 

 subjected to the serious attention of a vast army of smaller 

 foes, especially diptera and hymenoptera, which lay their eggs 

 in them, the caterpillars from these eggs devouring the internal 

 organs of the larvae, and, after maturing thereon and killing 

 their host, pupating either in the body or directly after leaving 

 it. The destructive powers of some of the smaller species are very 

 great. One minute species lays its eggs in the newly-hatched 

 larvae of Melitaea aurinia, in June, and, according to Wolfe, after the 

 larva stops feeding preparatory to hybernation, the parasite forms its 

 cocoon inside the web spun by the larva, in which to hybernate, and 

 the latter of course dies. The imagines of these ichneumons emerge in 

 spring, sting fresh M. aurinia caterpillars, and, so rapidly are their own 

 metamorphoses completed, that even a third brood of the parasites 

 will attack the same batch of larvae before the latter are full-grown. 

 The destruction caused by such parasites can readily be understood. 



Many peculiar structures are to be observed in butterfly larvae. 

 We have already referred to the chin-glands — eversible bladder-like 

 glands hidden in a slit on the ventral surface of the prothorax, which 

 are everted when the larva is disturbed, but which appear to have no 

 power of emitting any fluid, although it is possible that some scent may 

 render them of service as a means of protection to the larvae possessing 

 them, and which appear to be general among Nymphalid larvae. 

 But the most striking of the eversible glands in the butterfly larvae arc 

 the well-known osmateria of the larvae of Papilionids, Parnassiids and 



