Mimicry and Warning Colours in Grasshoppers. 127 



perfect in time, as successive casual variations in the 

 same direction increased the resemblance. 



The stick-insect is perhaps the most perfect ex- 

 ample where resemblance to an inanimate object 

 has been the result aimed at, so to speak, by nature ; 

 the resemblance of the volucella fly to the humble- 

 bee, on which it is parasitical, is the most familiar 

 example of one species growing like another to its 

 own advantage, since only by means of its deceptive 

 likeness to the humble-bee is it able to penetrate 

 into the nest with impunity. These two cases, 

 with others of a similar character, were first called 

 cases of " mimicry " by Kirby and Spence, in their 

 ever-delightful Introduction to Entomology — an old 

 book, but, curiously enough in these days of popular 

 treatises on all matters of the kind, still the only 

 general work on insects in the English language 

 which one who is not au entomologist can read 

 with pleasure. 



A second case of mimicry not yet noticed by any 

 naturalist is seen in another grasshopper, also 

 common in La Plata (Rhomalea speciosa of Thun- 

 berg). This is an extremely elegant insect; the 

 head and thorax chocolate, with cream-coloured 

 markings ; the abdomen steel-blue or purple, a 

 colour I have not seen in any other insects of this 

 family. The fore wings have a protective colour- 

 ing ; the hind wings are bright red. When at rest, 

 with the red and purple tints concealed, it is only a 

 very pretty grasshopper, but the instant it takes 

 wing it becomes the fac-simile of a very common 

 wasp of the genus Pepris. These wasps vary 

 greatly in size, some being as large as the hornet ; 



