40 Mr. E. B. Poulton's 7iotes upon the colours 



There is also a period in which the usual attitude must 

 be dangerous to Geometer larvae feeding upon trees. I refer 

 to the time when the young larva feeds and rests lupon the 

 leaf and does not retire to the stem. At this time the 

 rigid position and the attenuated body attached by the pos- 

 terior end to the surface or edge of a leaf would tend to 

 attract attention. At the same time it is likely that 

 larvae have, as a rule, most to fear, in these early stages 

 of growth, from their deadliest enemies, hymenopterous 

 and dipterous parasites. These parasites appear on the 

 wing, as far as I have observed, at the same time as the 

 lepidopterous imago, and therefore it is probable that 

 the larvae in which their eggs are laid must be very 

 young. Further, when larvae possess a special apparatus 

 for driving away Ichneumons, &c., the protective struc- 

 tures are well developed in early stages. 



Indeed, in Dicranura vinula the protrusible fiagellaare 

 of the greatest relative size in the young larva, and 

 gradually become of less importance during growth, 

 until it is rare to find the structures of any functional 

 value in a larva much more than half-grown. In nearly 

 all cases the flagella have ceased to be protrusible before 

 the larva is full-grown. This follows from natural 

 causes, and holds good when the structures have not 

 been injured by other larvsB of the same species. 



Of course the need of protection from birds remains 

 through life, and is doubtless more necessary as the size 

 of the larva increases and renders it more conspicuous. 

 But in early stages there is the additional need of pro- 

 tection from parasites. 



The objects usually met with upon leaves have an 

 irregular shape, with a frequent tendency towards the 

 spiral form. Such are, parts of the leaf accidentally 

 injured and curled up, spiral or imperfectly cylindrical 

 cases formed by many larvae, the excrement of birds and 

 snails. Nothing could be more unlike the usual attitude 

 of a Geometer larva. As to colour, the leaf-fragments 

 and larval cases are brown, the excrement of snails dark, 

 while that of birds is rendered conspicuous by irregular 

 white patches on a dark ground. Of course the usual 

 attitude can be retained by larvae of a green colour, for 

 these would be almost invisible against the background 

 of the leaf. It was very interesting therefore to find the 

 green larvae of E. omicronaria in the normal position 

 whenever I observed them. I cannot be sure that they 



