190 'ELEMENTS OF COMPARATIVE ZOOLOGY. 



cared for by the workers, which, as the name implies 

 perform all the labor of the colony. They obtain the 

 food, take care of the immature insects, build the nests, 

 and carry on the wars. In their battles some ants always 

 take prisoners, and these are kept as slaves. Some species 

 of ants have depended on slaves so long that they are only 

 able to fight, while did the slaves not feed them they would 

 starve. No group of insects will better reward careful 

 study than these. 



The digger-wasps make mines in the earth or in wood in 

 which they lay their eggs, usually placing with the eggs a 

 supply of food for the young. Some use as food pollen 

 and nectar of plants, while others store up insects or spiders 

 which have been so stung that they are paralyzed, not 

 killed. In this way the food will keep for a long time. 



The true wasps are some solitary, some colonial, and in 



FIG. 91. Sand- wasp (Sphex). 



the colonial forms we find again, as in the ants, males, 

 females, and workers, the workers being winged. Most of 

 these true wasps (and hornets are wasps) build nests usu- 



