Economic Importance of Animals 547 



example of this is the cattle tick which is able to transmit the cause of 

 Texas fever, the loss from which amounts to over $100,000,000 annually 

 in the United States. 



The daddy longlegs or "harvestmen" (Fig. 138) feed on living insects 

 and are thus of economic importance. Many of us as children have 

 asked these interesting animals this question: "Which direction shall I 

 go to hunt the cows?" We watched carefully to see which of the eight 

 legs was moved. This was supposed to be the direction of our bovine 

 search. Naturally and invariably, they had not been good herd masters 

 for their leg movements always led us in the wrong direction. 



The black widow spider is quite poisonous and is said to have caused 

 a number of deaths. The web of certain spiders is used in the manu- 

 facture of certain scientific instruments. Gomstock states that the 

 tarantula or "banana spider" is not capable of seriously injuring man. 

 If this is true, undoubtedly many fingers have been needlessly ampu- 

 tated and many hours of anxiety wasted. 



•The horseshoe crab or king crab (Limulus) of our Atlantic Coast 

 feeds on worms and is used as hog feed and fertilizer (Fig. 136). 



Class Insecta or Hexapoda 



The economic importance of insects is so great and varied that only 

 a few representative examples can be given. For a more complete dis- 

 cussion, textbooks in entomology and governmental publications are 

 suggested for references. 



General Usefulness of Beneficial Insects. — Tannic acid, secured from 

 certain galls produced on plants by insects, is used for tanning animal 

 skins for leather or fur. Many galls (Fig. 271) produced by insects 

 contain ingredients for dyes and inks. Most of the common fruits, 

 vegetables, and many ornamental plants are pollinated by insects. In 

 order for clover seed to develop from clover flowers, the latter must be 

 visited by some insect, usually some kind of bee. It has been observed 

 that the production of fruits and seeds is materially increased if there is 

 a hive of bees near by. This is quite profitable because the bees collect 

 the nectar from the flowers and make it into honey, and in collecting 



Fig. 271. — Several species of common galls produced on plants by insects of the 

 order Hymenoptera. 1. Blackberry seed gall [Diastrophus cuscutaeformis) ; 2. 

 knot gall {Diastrophus nebulosus) ; 3, mealy rose gall (Rhodites ignotus) ; 4, oak 

 bullet gall {Holcapsis globulas) ; 5, mossy rose gall {Rhodites rosae). From 

 Viereck: Insects of Connecticut, State Geological and Natural History Survey, 

 Bulletin 22.) 



