502 



Saw-flies, Gall-flies, Ichneumons, 



they are familiar with the details of the landscape in the district they inhabit. 



Fair eyesight and a moderately good memory on their part are all that need 



be assumed in this simple explanation of the problem." 



In the last of Sharp's divisions, on the basis of habit, are those solitary 



wasps that make nest-tunnels in wood or the stems of plants. In the pith 



of various kinds of cane-bearing plants, as brambles, blackberries, etc., 



may often be found the tunnels (Fig. 707), provisioned with plant-lice or 



other small homopterous bugs, of various small 

 wasps of the families Mimesidae and Pemphredo- 

 nidae. The Mimesids have a petioled abdomen 

 and look like little Sphecids; the Pemphredonids 

 are shining black. The family Crabronidae, a 

 rather large group of solitary wasps distinguished 

 by having only one closed submarginal cell in 

 the fore wings, includes many wood-borers. Very 

 common in sumac-branches, according to Corn- 

 stock, are the nests of slender yellow-banded Tri- 

 poxylon jrigidum; the cells are separated by mud 

 partitions. The Peckhams found two slender- 

 waisted, black species of Tripoxylon common near 

 Milwaukee, namely, T. albopilosum, f inch long, 

 with tufts of snowy-white hairs on the fore legs, 

 and T. rubrocinctum, a little smaller and with a red 

 band about the body. Although these wasps are 

 normally wood-borers, they will use convenient 

 cavities in any material; rubrocinctum was found 

 using crevices in the mortar of a brick house, 

 and the straw of a stack where thousands of 

 the cut ends of the straws offered attractive 

 clean nesting-holes; albopilosum was found nest- 



FIG. 707. Nest-tunnels of ing in holes made by beetles in posts and trees, 



two carpenter -wasps. A, j^t never i n straws; a third common species, 

 Monobw quadridens (Eume- . 



nidae) ; B, Stigmus jraternes bidentatum, seemed to nest only in burrows tun- 

 (Pemphredonidas). (After ne i e d by itself in the stems of plants. Another 

 Comstock; natural size.) . ,, 



carpenter-wasp, common in the eastern states, 



is the large Eumenid species, Monobia quadridens, which drills a tunnel in solid 

 wood, dividing it into cells by transverse partitions (Fig. 707, A). The species 

 of the genus Crabro make their nests especially in the canes of blackberry- 

 and raspberry-bushes. The Peckhams found that Crabro stirpicola did 

 much of its work at night, something not observed in the case of any other 

 solitary wasp. This species provisioned its cells with various species of 

 flies. 



