upon lepidopterous larva, &c. 313 



larvae which had been previously fed upon privet, &c. 

 The converse relation does not hold, for Mr. Grut 

 informs me that a larva which he found upon holly ate 

 privet with complete readiness. So also S. ocellatus 

 found upon sallow will always eat apple, and vice versa, ; 

 but I feel sure that in either case it would starve without 

 touching laurel or poplar. The last observation which 

 has come under my notice is the most remarkable. In 

 1885 I found a company of half-grown larvae of 

 P. bucephala feeding upon hazel, and I offered them 

 elm and Salix triandra, both of which were untouched ; 

 while they readily ate oak and Salix cinerea or S. 

 smithiana. In this case elm is a very common food- 

 plant of the species, perhaps the commonest at Oxford, 

 where the larvae were found. 



It therefore seems certain that the young larva on 

 hatching is in a far less specialised condition, as regards 

 its food-plants, than that which it will subsequently 

 reach. And this conclusion is supported by further 

 direct evidence, for it is well known that young larvae 

 will nibble leaves of plants upon which the species has 

 never been found, and may sometimes grow for a con- 

 siderable time upon such food ; while conversely the half- 

 grown larvae offered some new food do not usually give 

 themselves the chance of becoming adapted to it, for as a 

 rule they will starve without nibbling it in the least. 

 There is not much difficulty in imagining the conditions 

 under which a change of food-plant might occur without 

 the most obvious cause, i. e., alteration in range of distri- 

 bution. The instinct of laying eggs is far stronger 

 than that of laying them upon any particular species of 

 plant, for it is well known that in confinement moths 

 will lay eggs upon any surface which is at hand. 

 Similarly a deformed female moth could not seek a 

 scattered food-plant, but would be compelled to lay its 

 eggs in a limited area. So also, in the case of rare 

 plants, any larva wandering far before pupation would 

 render it possible that the moth might not find the 

 plant at all, and under these circumstances it could not 

 wait beyond a certain period without laying its eggs ; 

 and the same facts would probably hold for the last 

 eggs laid by many strong-flying species. Again, in certain 

 cases it is possible that the female moth may have been 

 deceived by the superficial resemblance between plants, 



TRANS. ENT. SOC. LOND. 1887- — PART III. (SEPT.) Z 



