214 THE BIOLOGY OF INSECTS 



comparatively lowly family of the Sawflies (Tenthredinidae) 

 whose larvae are caterpillars (Fig. 76, b) feeding on leaves. 

 The habits of Australian species of Perga have been described 

 by R. H. Lewis (1836) and W. W. Froggatt (1891, 1918). 

 The female Perga lewisii lays about eighty eggs in an incision 

 cut between the two surfaces of a gum-tree leaf, and rests 

 on the leaf until the eggs are hatched ; after this she follows 

 the young caterpillars about as they feed, " sitting with 

 outstretched legs over her brood, preserving them from the 

 heat of the sun, and protecting them from the attacks of 

 parasites and other enemies.'* When fully grown the larvae 

 crawl down to the ground-level and spin cocoons for pupa- 

 tion in the soil. In the later stages of larval growth, these 

 caterpillars are no longer guarded by their mother, but 

 they continue to feed and move in companies so that they 

 may still be regarded as a family living to some extent at 

 least a common life. Such gregarious habits, often resulting 

 from the limited space available on the food-plant, are dis- 

 played by many sav^y caterpillars, as well as by caterpillars 

 of moths and butterflies (Lepidoptera). The local migra- 

 tions of swarms of larvae of the Antler Moth (Chareas 

 graminis) or the Vapourer {Orgyia antiqua) are impressive. 

 Members of such communities move together, apparently 

 guided by contact, their behaviour suggesting that they 

 should be regarded less as a family than as a flock. The 

 family association among untended larval insects seems most 

 apparent in cases where the young creatures by their united 

 labour spin a silken web over the twigs and leaves of their 

 food-plants, and live together on this shelter, a kind of nest 

 not provided by the parent but made by members of the 

 family. The caterpillars of the Peacock Butterfly {Vanessa 

 to) afford illustrations of this habit in their younger stages, 

 while the caterpillars of the Lackey Moth (Clisiocampa 

 neustria) and the Small Ermines (various species of Hypono- 

 meuta) practise it throughout larval life. The silken 

 cobweb-like habitations of numerous families of the last- 

 named group are often so close together that the plants on 

 which they feed, a hawthorn hedge, for example, appear 



