112 FOURTH ANNUAL REPORT OF 



THE AILANTHUS SILKWOEM— Artacws ISamia} cynthia, Hiibn. 



(Lepidoptera, Borabycidje.) 



Of the diiferent worms which have been introduced from Asia, either 

 into Europe or America, the Ailanthus worm is the only si)ecies which has, 

 so far, proved hard}-; or which has become fullj- acclimated. Indeed it 

 seems to possess the same vigor of constitution so characteristic of the tree 

 upon which it feeds, and which enables that tree to flourish on all kinds of 

 soil and in widely- different latitudes. This merit at once gives it a claim 

 to our attention. 



DIFFERENCE BETWEEN THE CASTOR BEAN AND AILANTHUS SILKWORMS. 



There are two insects wdiich very closely resemble each other. One 

 was brought from India, and feeds on the Castor Bean (Bicinus communis). 

 It is domesticated in Hindostan and was introduced into France b}^ M. 

 Milne Edwards in 1854, and was tested at Paris, and at many other points 

 in France, Italy, Spain and Algeria. The silk is soft and glossy, and the 

 worm goes through its changes with great rajjidity, producing four or five 

 generations annually. The rearing of this insect was soon abandoned in 

 Europe, because in the first place it had no advantage over the Ailanthus 

 worm, and in the second, there was no prospect of obtaining, in that coun- 

 try, any great <|uantity of a raw material which depended on the Castor 

 Oil plant foi' its production ; for there, as with us, the jjlant is only annual, 

 and kills down each winter. It has been ascertained, however, that the 

 worm will feed and flourish on Lettuce, Chickory, Willow and Teasel (^Dip- 

 sacvs.). 



This insect was first figured in 1804 bj^ the English botanist Eoxburj^,* 

 who confounded it with the genuine cynthia under consideration. It like- 

 wise feeds upon the Ailanthus, and the resemblance to cynthia in all stages, 

 is so great, that it might well be considered as but a Castor .Bean feeding- 

 variety ; the more esjDecially as both insects are known to vary greatl}^, 

 and that in its domesticated state in Bengal, 7'icini acquires an orange color, 

 and looks quite different to what it does in the feral state.f The hybrids 

 of the two are also quite vigorous and fertile inter se. But in 1857 M. 

 Gruerin-Meneville pointed out what he considered sufficient specific differ- 

 ences, and the Jiicinus-feedmg from is now known, to entomologists as 

 Samia ricini, G-M. These difterences may be briefly set forth as follows : 

 While the egg of cynthia is covered with dark particles, that of ricini is im- 

 maculate. The full grown larva of cynthia is of an emerald green, with 

 black specks, and dark freckles; while that of ricini is of a pale azure and lacks 

 the spots. The cocoon of the former is larger, more compact and of a paler 

 gray than that of the latter, and while the former jjroduces but two or at 

 the most three broods, the latter produces five or six, annually. The moths 

 when closel}" examined will be found to differ in some essential points : 

 Cynthia has separated white tufts on the abdomen, while ricini has them 



♦'I'nms. Linu. Sue. of Loudon VI, p. ii, pL III. 



tSee also .some iuteresfing observations bv Dr. A. WaUace, in a paper "ou some variations ob- 

 served in Bombijx cynthia in 18«ti"— (Trans. London Ent. Soc. Feb. 4th, 1807.) where he gives reasons 

 I'.i- believing that both ricini and Guerinii are enfeebled varieties of cynth.a. 



