198 INSECTS 



best known and yet most widely employed. In the 

 body juices there is secreted an extremely irritating 

 material known as cantharidin which, when applied 

 to the skin, produces blisters or, taken internally, pro- 

 duces inflammatory conditions of the genito-urinary 

 system. Most of the blister beetles possess this prop- 

 erty to some extent, and a fresh specimen of any of 

 the common American species crushed upon the skin 

 will produce blisters; but the officinal preparations 

 are obtained from a European species, known as the 



FIG. 90. Spanish flies, Lytta vesicatoria, 



Spanish fly, Lytta vesicatoria, from the locality whence 

 most of the specimens come and from its vesicating 

 properties. These beetles come in great swarms when 

 they emerge and are on the wing for a few days only, 

 during which period the entire country is engaged in 

 gathering them in sheets on which they are killed and 

 dried, after which they may be preserved indefinitely. 

 The blistering property is dissolved out of the powdered 

 beetles with alcohol. 



Broadly stated there are no insects that are indis- 

 pensable to man; there are a few that are very use- 

 ful to him, aside from those that are plant pollinators, 

 and he makes use of a few others for which he has 

 substitute materials at hand and already in partial use. 



