PHYLUM ARTHROPODA. SPIDERS AND THEIR ALLIES 



273 



web; then from a point on this thread, other 

 threads are drawn out and attached in 

 radiating hnes. These threads all become dry 

 and smooth. On this foundation, a spiral 

 of sticky thread is spun. The spider stands 

 in the center of the web or retires to a nest 

 at one side and waits for an insect to be- 

 come entangled in the sticky thread; it then 

 rushes out and spins threads about its prey 

 until its struggles cease. 



Many spiders do not spin webs, but 

 wander about capturing insects, or lie in 

 wait for them in some place of concealment. 



Some spiders of 

 special interest 



Crab spiders (Fig. 164), although not all 

 are shaped like crabs, have the habit of walk- 

 ing sideways. Some are white or yellow in 

 color, and are said to favor flowers of simi- 

 lar color. Jumping spiders (Fig. 164) have 

 stout front legs for capturing prey; they are 

 famous for their peculiar antics during mat- 

 ing. Tarantulas (Fig. 169) are the giants of 

 the spider world, reaching a body length of 

 IVi inches and a leg spread of 9 or 10 inches. 

 Spiders of this size are able to capture small 

 birds. Tarantulas, under laboratory condi- 

 tions, are known to have lived over 20 years. 

 The trap-door spider digs a tunnel in the 

 ground about 6 inches deep and closes it 

 with a hinged door, not for the purpose of 

 trapping other animals, but to protect itself 

 from intruders. Wolf spiders do not wait 

 for prey to come to them, but go hunting for 

 their victims. They care for their young by 

 transporting them on their backs. 



More than 30,000 species of spiders are 

 known, of which about 3000 species live in 

 the United States. Only the black widow 

 and the tarantulas (Fig. 169) are harmful to 

 man in this country; and contrary to popular 

 belief, except for the tropical ones, the 

 tarantulas are not particularly dangerous. 

 The brightly colored garden spider is one of 

 the more beautiful species. House spiders 

 are considered a nuisance but are not dan- 

 gerous. 



OTHER ARACHNOIDEA 



King or horseshoe crabs 



Some of the strangest animals on earth 

 are these peculiar "living fossils" (Fig. 166), 

 whose close relatives died millions of years 

 ago. The common name horseshoe crab re- 

 fers to the heavy horseshoe-shaped carapace. 

 Actually, it is not a crab. The horseshoe 

 crab occurs along the Atlantic Coast from 

 Maine to Yucatan. It lives in shallow water 

 along the shores. Here it shoves its way 

 through sand and mud, where it hunts for 

 worms, bivalves, and other small animals on 

 which it feeds. 



Respiration is carried on with the aid of 

 book gills. The respiratory pigment of the 

 blood is hemocyanin which contains cop- 

 per, although this metal is recoverable only 

 in about a hundredth part in a million parts 

 of sea water. Oxygen combines with the 

 copper pigment to give the blood a blue 

 color when it is exposed to the air. 



Scorpions 



Scorpions (Fig. 166) are rapacious arach- 

 nids measuring from Vi to 8 inches in 

 length. They live in tropical and subtropical 

 regions, hiding during the daytime, but 

 running about actively at night. They cap- 

 ture insects, spiders, and other small ani- 

 mals. Larger animals are paralyzed by the 

 sting on the end of the tail. This sting does 

 not serve as a weapon of defense unless the 

 scorpion is hard pressed; and it is not used 

 to sting itself to death, as is often stated, 

 since its poison has no effect upon its own 

 body. The vital statistics of the Arizona 

 State Department of Health show that dur- 

 ing a twenty-year period, there were 64 

 deaths from scorpion sting. The state of 

 Durango, Mexico, reports more than 1700 

 deaths from scorpions over a period of 41 

 years. These records indicate that some 

 scorpions are killers and should be treated 

 with respect. 



The mating activities of scorpions are very 



