GENERAL ZOOLOGY 



Parasitic hymenopterans include many species which pass their develop- 

 mental stages as parasites within the bodies of other insects. Among these 

 parasitic forms are ichneumon wasps and braconid wasps (Fig. 15.34), which 

 usually deposit their eggs upon or within the bodies of a variety of other 

 insects. After the larvae hatch, they live parasitically in the body of the 

 host until their time of pupation; they then come to the surface and spin 

 cocoons from which adult wasps later emerge. Caterpillars are often found 

 covered with the minute cocoons of these parasites. Many times, an ap- 

 parently normal cocoon of one of the giant silkworm moths will be found to 

 contain not the pupa of the moth but that of an ichneumon wasp, whose larva 

 has completely devoured the caterpillar which spun the cocoon. The activi- 

 ties of such parasitic wasps have sometimes helped check outbreaks or 

 invasions of insect pests of economic importance. 



Non-parasitic wasps may be subdivided into solitary forms, in which there 

 is no colonial organization, and social wasps, which live in colonies like those 

 of bees and ants. Mud daubers of the genus Sceliphron are solitary wasps that 

 build a nest of mud fashioned into several tubes. When one of these tubes is 

 completed, the wasp collects small spiders, which she paralyzes with her sting 

 and with which she fills the tube. She then deposits a single egg in the outer 

 end of the tube before sealing it with mud. When the larva hatches, it uses 

 the spiders as food, eventually pupating and finally emerging as a winged 

 adult, which gnaws its way out of the tube. Only females are active in the 

 nest-building operation; males apparently die soon after mating. Digger 

 wasps, excavating subterranean burrows which they provision with paralyzed 

 insects, oflTer another example of hunting and food-storing activities (Fig. 

 15.35). 



Among social wasps, species of the genus Polistes represent a simple type 

 of social organization. They build nests of paper, which they make by chew- 

 ing wood fibers and mixing them with saliva. A female Polistes, after hiber- 

 nating through the winter, begins to construct a nest which bv the end of the 

 summer may reach a diameter of a foot or more. The nest is a plate-like 

 group of individual paper-walled cylinders, generally fastened to some support 

 by a slender stalk. The single female, or queen, which begins the construc- 

 tion, is soon aided in tending the young and adding to the nest by other 

 females, the infertile workers, which hatch from her eggs. The males are 

 drones, which do not work and which die soon after mating. The nests of 

 hornets that hang from the limbs of trees are composed of a series of paper 

 combs essentially like those of Polistes but enclosed in a common covering. 



Among bees there are both solitary and social species and others that show 

 transitional stages. Thus, it is possible to establish theoretically the steps 

 through which the highly organized honeybee colony may have evolved. In 

 solitary species each female constructs her own separate nest, in which an 

 egg is laid and where food is either stored or brought to the larva during 

 its development. Some of these solitary species show a tendency toward gre- 

 gariousness, suggesting the beginnings of social life. They build many nests 



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