THE ANTS, BEES, AND WASPS 91 



are the so-called "ant eggs," which are the objects of much 

 solicitude when a nest is exposed. The imagoes are unable 

 to escape from the pupal case without the help of the workers. 

 The males and females are at first winged (Fig. 59, B) and 

 take flight in great numbers into the air on some warm day 

 in spring. At this time fertilization occurs. On their return 

 the males soon die, and the females, stripping off their wings 

 (Fig. 59, C), become the mothers of colonies. The females 

 can be distinguished from the workers by their larger size 

 and the presence of well-developed ocelli. 



Many other insects, especially beetles, live habitually in 

 the nests of ants, and, in some cases at least, seem to per- 

 form some useful function, — acting as scavengers, for 

 instance. These cases, like that of the bumblebees and guest 

 bees, may be cited as illustrations of commensalism (Lat. 

 com (=cum), "together"; mensa, "table"), an association 

 of one species of animal with another for support or advan- 

 tage, but not as a parasite. 



An illustration of cooperation between two different spe- 

 cies of animals is shown in certain ants and aphids. As 

 mentioned in Chapter IV the cornfield ant (La'sius, Fig. 59) 

 collects eggs and young of a species of aphid and guards them 

 throughout the winter in burrows, thereby providing a con- 

 stant supply of honeydew. Some ants build a shelter of wood 

 pulp or mud over colonies of aphids, which are crowded 

 on a branch, from which they derive their nourishment. 

 These aphids are often spoken of as the cows of the ants. 

 In these cases the relation between the ants and aphids is 

 clearly of a more intimate character than the association 

 of the bumblebees and guest bees ; and the advantages 

 are mutual, for while the ants secure a constant supply 

 of food, the aphids receive care and a certain amount of 

 protection against their enemies. This association is spoken 

 of as symbiosis (Gr. syn, "together" ; bios, "life"). 



