FAMILY LIFE 215 



covered by a continuous sheet of fine threads, and the 

 families of caterpillars are merged in a great, if unorganised, 

 society. 



Returning to the Hymenoptera that store in their nests 

 provision for their grubs by burying or immuring paralysed 

 or dead caterpillars and other prey, it is of interest to find 

 traces of the development from this common habit to that of 

 actual care for the grubs after hatching. In his most instruc- 

 tive work on *' Social Life among Insects," W. M. Wheeler 

 (1923) draws attention to the habits of certain African 

 solitary wasps (Synagris) as described by E. Roubaud 

 (191 6) and J. A. Bequaert (191 8). These wasps make mud- 

 nests on such surfaces as the thatch of huts, and the female 

 '' under normal conditions, when food is abundant, lays an 

 egg in her mud cell, fills it in the course of a few days with 

 small paralysed caterpillars, and then closes it." But when 

 prey is scarce the mother-wasp guards the egg, and after 

 it hatches, collects a few caterpillars at intervals so as to 

 provide food for the grub during the greater part of its 

 period of growth. When the larva is about three-quarters 

 grown, the mother " immures it in its cell with the last 

 supply of provisions." In such species therefore we see 

 actual transition from the storing of food for grubs which 

 the mother will never see to actual care and feeding of the 

 young. This has apparently become the normal habit of 

 one species, Synagris cornuta, as the female feeds her off- 

 spring '' from day to day with pellets made up of a paste of 

 ground-up caterpillars." The habit of bringing food to the 

 larvae through their period of growth is well known in the 

 Sphecoid digging-wasps of the genus Bembex. The habits 

 of the North American B. spinolae have been vividly described 

 by the Peckhams, who dwell on the female's " habit of 

 feeding her young from day to day or rather from hour to 

 hour as long as it remains in the larval state." These 

 insects catch two-winged flies which are placed in the nest 

 after having been killed by stinging. Wheeler remarks how 

 the number or size of the victims is increased ** as they are 

 needed by the growing and increasingly voracious larva." 



