20 
THE STUDY OF INSECTS. 
then lets go its hold with its feet and sails away. That these 
spiders travel long distances in this manner has been shown 
by the fact that they have been seen floating through the 
air at sea far from land. 
Representatives of nearly thirty families of spiders have 
been found in the United States. But some of these fami¬ 
lies include only rare species, and others arc represented by 
so few species that we cannot discuss them here. The 
greater number of our spiders belong to the eleven families 
described below. The following table will aid the student 
in separating these families. 
TABLE FOR SEPARATING THE PRINCIPAL FAMILIES OF 
SPIDERS. 
A. Claw of the mandibles moving vertically; four lung-slits present. 
( Tarantulas .) p. 27. Theraphosid^e. 
AA. Claw of the mandibles moving horizontally; only two lung-slits 
present, but with a single spiracle or a pair of spiracles also. 
B. Eyes equal or nearly equal in size, and usually arranged in two 
rows. 
C. Feet furnished with two claws (Fig. 28). Spiders which 
do not spin webs for catching prey. 
D. Second pair of legs not so long as the fourth pair. 
E. Maxillae with a concavity or furrow (Fig. 29). Spiders 
which live on the ground, p. 29.DRASSIDJE. 
EE. Maxillae convex (Fig. 32). Spiders which live chiefly in 
silken tubes on bushes, p. 30. Clubionid.e. 
DD. Second pair of legs as long as or longer than the fourth 
pair. (The crab-spider si) p. 40. Thomisid^E. 
CC. Feet furnished with three claws (Fig. 38). Spiders which 
spin webs for catching prey. 
D. The caudal pair of spinnerets very long, and two-jointed. 
Spiders which make irregular webs with a tube or hiding- 
place at one side, from which they run on the upper surface 
of the web, to catch their prey. p. 30. AgalenidjE. 
DD. All of the spinnerets short. 
E. With cribellum and calamistrum. Spiders making webs 
in which there are curled threads, or double threads. 
