Phylum Arthropoda 513 



to carry them to a new destination. The trap-door spiders build web- 

 hned tubes in the earth, some with an efficient closing door. One group 

 of spiders, the bolas spiders, catches prey by means of a miniature bola, 

 which is a thread with a sticky mass at its end. This is thrown at some 

 unwary insect which flies within range. In all cases, the prey when 

 caught by the spider is quickly killed by the poison from the poison 

 glands, and the body juices are sucked. 



Complex behavior patterns often precede the actual transfer of 

 the sperm from the male to the female. In various ways, the sperm is 

 transferred to the palpal organ of the male. It is then transferred directly 

 to the epig}'num of the female in some forms ; in others, the female must 

 pick it up. Often the female kills the male after mating. The eggs are 

 usually encased within a cocoon which may be deposited, hung on a web 

 or twig, or simply carried about by the female. Development is direct 

 with miniatures of the adults emerging from the eggs. 



Other Arachnida. — In addition to the numerous conspicuous and 

 often colorful spiders, there are many other important arachnids, some 

 of which are of great economic significance. 



The scorpions (order Scorpionida) are found throughout the 

 southern United States and are particularly abundant in the southwest. 

 They are easily recognized by their long, conspicuously segmented abdo- 

 men which is elongated posteriorly and which terminates in a sting. 

 This elongated portion of the abdomen is carried arched above the body. 

 Connected to the sting is a poison gland by which the animal's prey 

 is killed. The poison of all species is irritating to human beings and a 

 few species are actually dangerous. The poison is a neurotoxin which 

 may be fatal to children. The pedipalps terminate in pincers or chelae 

 by which the prey are grasped. The young are born alive and climb 

 on the back of the mother where they remain until after the first molt. 

 The scorpions feed on insects and other small invertebrates. 



The pseudoscorpions (order of Pseudoscorpionida) are small forms 

 which superficially resemble scorpions in their possession of enlarged 

 chelate pedipalps ; however, they have no elongated abdomen or sting. 

 Like the spiders, they possess silk glands by which they can spin webs ; 

 but these glands are not homologous with the silk glands of the spiders. 

 Although these animals are quite abundant, their small size makes them 

 relatively inconspicuous. Occasionally they are found in houses, but 

 more often they are found under logs or stones or in leaf mold. Their 

 prey commonly consists of mites or other tiny arthropods. 



