COMMUNITIES IN DRY, OPEN LANDS 461 



tropical regions. While the ants of the forests seldom go below the 

 surface of the soil, all the grassland species build their nests in the 

 ground; they dig their burrows 3-5 m. deep and sometimes reach the 

 ground-water level. The earth piles up in conspicuous rings about the 

 entrance. Their work supplements that of the burrowing rodents, ac- 

 complishing the same end in dry soil that earthworms do in moist 

 ground; they care for the constant renewal of the fertile surface layer, 

 which is especially important for the germinating plants; they promote 

 the circulation of air in the ground and the penetration of rainwater; 

 they fertilize the soil with their excrement and metabolic wastes. 



Ants are different from termites in that they are not exclusively 

 plant feeders, but take food of every kind, and especially animal food. 

 In the times of greatest drought, their menu is limited; it is on account 

 of this that certain ants that store food live in the dry steppes. Tetra- 

 morium caespitum 56 carries seeds into its nest in Germany only in the 

 warmest summers ; in Algiers this species regularly stores large quanti- 

 ties of grain. In the Mediterranean lands, the grain-gatherers of the 

 genus Messor always do this, as do the North American species of 

 Pogonomyrmex. The so-called honey ants have a peculiar method of 

 storing up supplies ; they feed individual workers so full of honey that 

 the crop makes the abdomen swell up like a ball, and in times of need 

 this stored honey is regurgitated. This striking habit has been con- 

 vergently developed in semi-desert areas in North America, South 

 Africa, and Australia by species only distantly related. 



Ants and termites are among the "key industry" animals in the 

 open lands and form the base of important food pyramids. Mammals 

 and birds track them even into their nests and dig them out, together 

 with their larvae and pupae. The pampas woodpecker {Colaptes 

 campestris) , and the South African ground woodpecker (Geocolaptes) 

 live almost entirely on ants, as do several mammals which have al- 

 ready been mentioned. The number of ant- and termite-eating animals 

 becomes even greater when the winged sexual forms swarm forth at the 

 beginning of the rainy season, some by day, some by night. Predaceous 

 beetles, frogs, toads, 57 and lizards lie in wait for them on the ground, 

 while wasps, innumerable birds, from hawks to goatsuckers, and a host 

 of bats, pursue them in the air. 



The richest bee fauna appears to be developed in sunny steppes 

 with loose soil; in damp ground the food supplies for the brood might 

 be endangered by mold. 58 Burrowing wasps likewise play a large part 

 in steppe regions; thus, more than 80 species of Cerceris occur in South 

 Africa. Their brood parasites are found with these Hymenoptera, such 

 as the mutillid wasps, the bombyliid flies, and the blister beetles 



