PROTECTIVE AND AGGRESSIVE MIMICRY 267 



form to lay eggs in the nest of that which it resembles, 

 so that its larvae live upon the food stored up by the 

 latter or even upon the larvae themselves. The bold- 

 ness of these enemies sometimes depends upon the 

 perfection of their disguise. Thus the larvae of flies 

 of the genus Volucella live upon the larvae of bees and 

 wasps. Volucella bombylans occurs in two varieties, 

 which prey upon the humble-bees, Bombus muscorum 

 and B. lapidarius, and are respectively like these Hy- 

 menoptera. The resemblance is very perfect, and the 

 flies enter the nests to lay their eggs. Volucella inanis 

 is less like the common wasp (Vespa vulgaris), and only 

 dares to lay its eggs in the evening at the entrance of 

 the nest, so that the larvae may crawl in, or they or 

 the eggs may be accidentally carried in by the wasps. It 

 is said that the resemblance often fails to conceal the 

 fly, which is then killed by the wasps. 1 Some Hyme- 

 noptera also live upon the labours of other species of 

 the same order, and often resemble the species they 

 delude. Thus, bees of the genus Psithyrus closely 

 resemble humble-bees (Bombi) : they lay their eggs 

 in the nests of the latter, and their larvae are developed 

 among those of the Bombi.* 



1 Mr. C. R. L. Perkins attributes the cautious habits and frequent 

 failure of V. inanis to the acuteness and ferocity which distinguish 

 the wasps from humble-bees. 



2 Mr. Perkins considers that the Mimicry is intended to enable the 

 Psithyri to leave the nests after emerging from the pupa, rather than 

 to enable the mature females to deposit their eggs in it. 



