154 A NATURALIST IN THE GREAT LAKES REGION 



many inhabitants dig in to get down to the moist, cool sand a 

 few inches below the surface. The burrowing spider does this, 

 coming out at dusk to hunt. Its holes are one-eighth to one-half 

 inch in diameter and 5 or 6 to 20 inches deep. The hole is sur- 

 rounded in early morning by moist 

 dabs of sand thrown out in excava- 

 tion. The full-grown spider, legs 

 extended, nearly covers the palm of 

 your hand. It is colored like the 

 sand. Here also the black digger 

 wasp, Anoplius diver sus, makes its 

 FIG. 150 The bee fly, Exoprospa. holes in which to rear its young and 



After Williston. stocks them ^^ spiders for f Qod 



for the larvae. The holes are shallow and the heat serves to 

 incubate the eggs. Two other digger wasps of a smaller sort, 

 Microbembex monodonta (Fig. 149) and M. spinulosa (Fig. 67), 

 or Bembex spinolae, excavate holes that are so 

 abundant in spots the surface layer is per- 

 forated like a sieve. They are the most strik- 

 ingly characteristic features of this area and it 

 may properly be designated the digger wasp 

 association. Not that the digger wasps are 

 not elsewhere found. But they are nowhere 

 else so conspicuous and dominating a part of 

 the animal consocies. Bee flies (Fig. 150) 

 hover over the groups of wasp holes, dipping 

 down to the surface every once in a while to 

 deposit eggs at the entrance of some wasp hole Willow-leaf beetle, 

 so that when the latter drags in flies to stock Disonycha quinquevit- 

 her nest the bee fly egg may be carried in, too. 

 The bee fly larvae live parasitically on the larvae of the digger 

 wasps. 



The low plants of the fore-dunes, sand reed, marram grass, 

 sarfd cherry, smooth and glandular willows, etc., are relatively 

 free from insect pests. Apparently the conditions under which 



FIG. 151. The 



