HYMENOPTERA 225 



season of the year, or a store laid up by the parent, provides 

 an unlimited supply for the new generations. Then, it would 

 appear, the ordinary process of reproduction may safely be 

 abridged. Hard conditions, on the other hand, such as scarcity 

 of food, or low temperature, require the reproduction of 

 fertilised eggs. It is generally believed that the queen-bee 

 has the power of producing either fertilised (female) or 

 unfertilised (male) eggs at pleasure, and that the worker-bees 

 can transform the larva of an ordinary worker into a queen 

 by a change of food ; the latter power is well authenticated, 

 and finds a parallel in other social insects (Termites). 



Mode of life, etc. — Bees, wasps, and ants furnish the most 

 familiar examples of insect-communities. Division of labour, 

 either among the members of a family or of a colony, has 

 at length resulted in the establishment of three kinds of in- 

 dividuals (males, females, and workers). Bees and ants are 

 remarkable for the complexity of their social organisation, and 

 for the many highly developed instincts which they employ for 

 the good of the whole society. Only the Termites, among non- 

 Hymenopterous insects, exhibit so well ordered a common life. 



Hymenoptera resemble in their external features some of 

 the miscellaneous collection of insects called Neuroptera, but 

 there is no proof of close relationship between the two orders. 

 The wings of Neuroptera, except in some minute forms, are 

 intersected in several directions by veins, so that a great many 

 small polygonal cells are produced; in the Hymenopterous 

 wing the number of the cells is limited. In Neuroptera 

 the waist is not narrowed, as in the majority of Hymen- 

 optera; and the first abdominal segment is not united with 

 the thorax. 



The simplest and most primitive Hymenoptera are those 

 with sessile abdomen (wood-wasps, saw-flies, etc.). A few of 

 these are gall-makers. Then comes the family of the gall-flies 

 \Cynipida), many of which lay eggs in the tissues of living 

 plants, where the irritation sets up abnormal growths. All 

 vegetable galls are not, however, produced by Hymenoptera. 

 Some are due to the attacks of Hemiptera {Aphis, Phylloxera), 

 Diptera (Cecidomyida), Coleoptera (some weevils) or Acarina 

 {Phytoptus). Some Cynipid^ are parasitic on other insects. 

 These lead up to the Ichneumons of various kinds. The 

 ruby-wasps {Chrysididce), and perhaps the Braconidse, among 

 p 



