COTTONWOOD ASSOCIATION 



223 



species. Some bee-flies (Exoprospa) (Fig. 188) lay their eggs at the 

 entrances of the burrows of Microbembex. The roots of the beach grasses 

 are probably attacked by the larvae of snout-beetles (Sphenophorus) 

 (Fig. 189) (174) of which several species are very common in the vicinity. 

 The white grasshopper {T rimer otro pis maritima) (40) and the white tiger- 

 beetle (Cicindela lepida) are most characteristic. The long-horned 

 locust (Psinidia fenestralis) (Fig. 189) occurs commonly. 



b) Field stratum. — The field stratum is made up of animals that 

 occupy the grasses, sagebrush, and a few other xerophytes. Animals 



Digger- Wasps of the Cottonwood or White Tiger-Beetle Association 



Fig. 183. — Photograph of a number of the burrows of one of the digger-wasps 

 {Microbembex monodonta) at Pine, Ind. 



Fig. 184. — A digger-wasp {Bembex spinolae)) about twice natural size. 



Fig. 185. — A sectional drawing of a burrow of the digger-wasp {Bembex spinolae); 

 reduced (after the Peckhams, Wis. Geol. and N. H. Surv.). 



are few. An occasional red-legged locust (Melanoplus femur-rubrum) 

 occurs here. Midges, mosquitoes, and the flies which breed on the beach 

 rest on the leeward side of the grasses (169). Various native sparrows 

 are common in fall, feeding on grass and weed seeds. 



c) Shrub stratum. — On the young cottonwoods we find the crab- 

 spider (Philodromus alaskensis), often with its appendages stretched out 

 on the petiole or midrib of a leaf. The animals feeding on the cotton- 

 wood here are few. In early spring the willow blossoms are frequented 



