vii DEFENCES OF INSECTS 273 



vulgaris), but its disguise is less perfect, so that it 

 dares not venture within the portals of its model. It 

 lays its eggs at dusk at the entrance to the abode, 

 giving the larvae a chance of being accidentally carried 

 in by the wasps, or by creeping in of their own 

 accord. As it is, the presumption is said to often 

 cost the mother-fly her life, owing perhaps to the 

 slight failure of the imitative dress, or to the greater 

 intelligence of the wasp as compared with the humble 

 bee. Hymenoptera also mimic and live upon the 

 labours of home-building species of their own order. 

 Bees of the genus Nomada resemble Andrenidae, and 

 bees of the genus Psithyrus are almost exactly like 

 the humble-bees (Bombi] in whose nests they are 

 reared. On the banks of the Amazon Bates 

 found many of these " cuckoo " bees and flies, which 

 all wore the livery of working-bees peculiar to the 

 country. 



There are cases in which the welfare of the mimetic 

 species is promoted in another way. The insect that 

 resembles another does not injure the latter, but preys 

 upon an animal which accompanies it, or to whom the 

 species mimicked is indifferent. In the opinion of 

 Professor Meldola certain ant-like spiders from 

 Africa, described by Mr. Mansel Weale, are instances 

 of Aggressive Mimicry by spiders for the purpose of 

 preying upon flies, which are often found in company 

 with the ants, and upon which the latter are not 

 predatory. Both the ants and the flies are said to 

 visit the same trees in order to feed upon the sweet 

 secretions, and the former can mingle freely with the 

 flies without causing alarm. The spiders by mimick- 



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