TYPES OF PARASITISM 317 



(d) A third type of parasitism is met with among those social 

 insects which have themselves adopted a life of parasitism in the 

 colonies of other social insects. They parasitise a colony instead 

 of an individual of a species and obtain their food and that of 

 their larvae at the expense of supplies brought in by the members 

 of the colony. Social parasites occur among ants, bees, wasps 

 and termites, and their behaviour has been fully discussed in 

 numerous contributions by W. M. Wheeler. 



(e) Among solitary wasps and bees there is found an inter- 

 grading series between parasitism on the one hand and inquilinism 

 on the other. In many cases it is difficult to draw any hard 

 and fast lines between the several types of behaviour. In the 

 primitive Vespoid families Scoliidae, Thynnidae and Mutillidae 

 the parent insect seeks out insect larvae living in concealed 

 situations ; these they immobilise by stinging and then lay their 

 eggs upon them, and their larvae are parasitoids living externally 

 to their hosts. Most other solitary wasps store up in their nests 

 one or more insects which they have previously paralysed, and 

 attach one of their eggs to the body of the prey. The wasp 

 larva upon hatching behaves as an ectoparasite (or predator) and 

 devours the prey ; or, if there be several, it consumes them in 

 succession. This behaviour differs but little from that of the 

 Scoliid and other wasps except that the parent insect transfers 

 the prey from its natural habitat into the nest. Many parasitic 

 bees lay their eggs in the cells of other bees of allied genera, 

 among the stores of honey and pollen. The parasitic larva, 

 upon emergence from the egg, finds itself in close proximity to 

 the normal occupant of the cell. In cases studied by Graenacher 

 the parasitic larva has more powerful jaws than its rival, and 

 easily succeeds in destroying it. It then proceeds to consume the 

 food-supply and casts its enlarged mandibles with the first ecdysis. 

 There are, again, other so-called parasitic wasps whose larvae are 

 solely nourished upon the food-stores of the host, the parent 

 removing and destroying the egg or young larva of the host 

 preparatory to the emergence of its own offspring. In Sapyga 

 quinquepunctata and ♦S'. similis, which live at the expense of solitary 

 bees, both Fabre and Nielsen have shown that the long ovipositor- 



