COMBINATION OF MANY METHODS OP DEFENCE 275 



high as forty per cent., and a twentieth of a gramme 

 can be ejected if the caterpillar has not been irritated 

 for some days. Half grown individuals eject nearly 

 as much, but the fluid is weaker, containing about 

 thirty-three to thirty-five per cent, of acid. The rate 

 of secretion is slow ; two days and a half after the fluid 

 had been collected from two large caterpillars they only 

 yielded a fortieth of a gramme between them. 1 So far 

 as we know at present, no other animal secretes a 

 fluid containing anything which approaches this per- 

 centage of strong acid. 



The value of this strongly irritant liquid is suffi- 

 ciently obvious. I have seen a marmoset and a lizard 

 affected by it, and have myself twice experienced 

 sharp pain as the result of receiving a very small 

 quantity in the eye. Although the secretion is there- 

 fore useful as a defence against vertebrate enemies, it 

 is probably chiefly directed against ichneumons. 



The most deadly enemy of the larva of the Puss Moth 



The caterpillar of the Puss Moth is especially 

 attacked by an ichneumon (Paniscus cephalotes), which 

 attaches its shining black eggs to the surface of the skin. 

 These eggs are always fixed in such a position behind 

 the head that the caterpillar cannot bite them or the 

 maggots which hatch from them, and on a spot where 



1 For further details of this investigation see Report of British 

 Association at Manchester, 1887, pp. 765-66. 



