16 AMERICAN SPIDERS 



Every one of these living orders of arachnids occurs within 

 the limits of the United States. A few interesting peculiarities of 

 each should be noted. 



Scorpions. The scorpions are the most primitive members of 

 the land arachnids, and also the oldest, being known from Silurian 

 fossils that have an age of about four hundred million years. Among 

 the oldest is a species from fossil beds at Waterville, New York, 

 which was named Proscorpio osborni, and which was perhaps the 

 first animal to adjust itself to a land life in North America. This 

 ancient creature had no tarsal claws, and perhaps had not completely 

 divested itself of the external gills that characterize the related, 

 extinct eurypterids. 



The most obvious characteristic of the scorpion (Plate 4) is 

 the invariable presence of a poisonous sting on the end of the ab- 

 domen, which is narrowed to form an elongate tail. In life, the tail 

 is curved over the back, and the spinelike sting is directed forward, 

 always in position to attack its prey. The sting is generally used in 

 conjunction with the great pedipalpi, which are developed as pin- 

 cers to grasp and hold the victim. The venom of most scorpions 

 is capable of causing mild to severe local reactions. A few species 

 are known to cause pronounced neurotoxic reaction in man and 

 warm-blooded animals. Two species of Centruroides occur in Ari- 

 zona and are more notorious than the black widow for the virulent 

 nature of their sting, which often is serious or fatal in children. 



Scorpions produce living young that mount the back of the 

 mother and stay there until after their first molt, usually for a week 

 or more. During this time they do not feed, but rely for sustenance 

 upon the food stored in their bodies. The story that these little 

 creatures, weakly armed with tiny chelicerae, feed upon the body 

 juices of the mother, is a figment of some fertile imagination. An- 

 other fable is the belief that scorpions commit suicide by stinging 

 themselves when they are helplessly cornered or surrounded by a 

 ring of fire. 



Pseudoscorpions. The pseudoscorpions are so named because of 

 their superficial resemblance to true scorpions. They have the same 

 enlarged pedipalpi terminating in pinching chelae, but the seg- 

 mented abdomen is broadly rounded behind and is without trace 

 of whip or tail. The largest species are scarcely more than one 

 fourth inch in length, and most of the others are much smaller. 



