226 AMERICAN SPIDERS 



and they have become rather sluggish creatures that excel as am- 

 bushers. They have sacrificed ease of movement for a leisurely life 

 in flower heads or on the ground, and have lost the brushes of hairs 

 beneath their legs and the tarsal claw tufts present in their forebears. 



The species of Oxyptila and Xysticus (Plate 28) are pre-emi- 

 nently spiders of the ground; their colors, dull grays, brown, and 

 blacks, mingle with the leaves and organic debris of the soil. They 

 squeeze their flat bodies under bark and into cracks. The mottled, 

 greatly flattened species of Coriarachne simulate to a remarkable 

 degree the bark of trees or old wood of fences and houses on which 

 they hide. 



The ambushing crab spiders that live on vegetation and in 

 flowers are much more brightly colored than the ground forms, 

 but tend equally to cryptic coloration. The delicate green Synema 

 viridans, for example, lives on foliage, while some of the whitish 

 or colored species of Xysticus are distinctly flower forms. The 

 best-known flower spiders of the north temperate zone are the 

 numerous species assigned to three closely allied, often confused 

 genera, Misumena, Misumenops, and Misumenoides: handsome 

 white, yellow, or saffron-yellow creatures often marked with black 

 or red bands and spots. All are ambushers, obtaining their liveli- 

 hool by strategy. They are usually found in the heads of flowers; 

 there, simulating the phlegmatic assassin bugs, they lie immobile in 

 wait for insects seeking pollen or honey. Large and seemingly dan- 

 gerous bees and wasps, large-winged butterflies, and a host of 

 winged insects are seized and quickly dispatched by the pygmy 

 ambusher. 



In keeping with their habit of deception, these ambushers are 

 known to change color from white to yellow, to conform with the 

 substratum of their hunting ground. In this connection it should 

 be noted that while they may be found on a variety of colored 

 flowers, a very high percentage occur on white or yellow ones. In 

 the fall A. S. Pearse, the American ecologist, found that 84 per cent 

 of all the white spiders (perhaps of two or three species) were on 

 white flowers, and 85 per cent of the yellow spiders were on yellow 

 flowers. Only 6 to 10 per cent of the spiders were found on flowers 

 other than white or yellow. Being homochromous with their flower 

 station seems to bring them some advantage in their hunting, as 

 well as a measure of immunity from their enemies. It is well known 

 that flying insects avoid light-colored flowers in which sit dark 

 spiders or insects, or small dark objects placed there by investi- 

 gators. 



