11 VESPIDAE— SOCIAL WASPS HABITS 85 



Insects produced at this early period of the colony are exclusively 

 workers, i.e. imperfect females. They relieve the queen of 

 the task of supplying the larvae with food, and she henceforth 

 remains within the nest, being, it is said, herself fed by her 

 workers ; the society now rapidly increases in numbers, and fresh 

 combs are formed, the upper layer being always the oldest. 

 About the month of August, cells of larger size than those that 

 have previously been constructed are formed, and in these males 

 and perfect females are produced ; in a few weeks after this the 

 colony languishes and becomes extinct. When it is no longer 

 possible for the enfeebled wasps to carry out their tasks of feeding 

 the brood, they drag the larvae out of the cells and destroy them. 

 An uncertain number of queen-wasps seek protected nooks in 

 which to pass the winter, and each of these queens may be the 

 founder of a nest in the ensuing spring. It should be remarked 

 that de Saussure states that all the intermediate grades between 

 perfect and imperfect females exist, and Marchal's recent observa- 

 tions confirm this. There is in fact no line of demarcation 

 between worker and queen in the wasps as there is in the honey- 

 bee. Von Siebold long since drew attention to the existence of 

 parthenogenesis in certain species of wasps, and it appears prob- 

 able that it is of common occurrence. 



Our knowledge of the social life of European wasps has 

 recently been much increased by the observations of two French 

 naturalists, P. Marchal and C. Janet. The latter has given 

 an elaborate history of a nest of the hornet, showing the rate 

 and variations of increase in numbers. His observations on this 

 and other species indicate that warmth is of the utmost im- 

 portance to wasps ; the Insects themselves create a consider- 

 able amount of heat, so that the temperature of their abodes is 

 much greater than that of the air. He considers that in Europe 

 an elevated temperature is essential for the development of the 

 individual,^ and that the chief object of the various wrappers of 

 paper with which the Insects surround their nests is to keep 

 up this high temperature. These envelopes give a great deal 

 of trouble to the Insects, for they have to be repeatedly 



' Hence probably the great difference in the abundance of wasps in different 

 years : if a period of cold weather occur during the early stages of formation of a 

 wasp family, operations are suspended and growth delayed ; or death may even 

 put an end to the nascent colony. 



