THE ECONOMIC IMPORTANCE OF ANIMALS 209 



is the natural enemy of the orange-tree scale, the ladybug, or 

 ladybird beetle. In New York state it may often be found feed- 

 ing upon the plant lice, or aphids, which live on rosebushes. The 

 carrion beetles and many water beetles act as scavengers. The 

 sexton beetles bury dead carcasses of arrimals. Ants in tropical 

 countries are particularly useful as scavengers. 



Insects, besides pollinating flowers, often do a service by eating 

 harmful weeds. Thus many harmful plants are kept in check. 

 We have noted that they spin silk, thus forming clothing ; that 

 in many cases they are preyed upon, and that they supply an 

 enormous multitude of birds, fishes, and other animals with food. 



Use of the Toad. The toad is of great economic importance 

 to man because of its diet. No less than eighty-three species of 

 insects, mostly injuri- 

 ous, have been proved 

 to enter into the dietary. 

 A toad has been ob- 

 served to snap up one 

 hundred and twenty- 

 eight flies in half an 

 hour. Thus at a low 

 estimate it could easily 

 destroy one hundred 

 insects during a day 

 and do an immense ser- 

 vice to the garden dur- 

 ing the summer. It has 

 been estimated by Kirk- 

 land that a single toad may, on account of the cutworms which 

 it kills, be worth $19.88 each season it lives, if the damage done 

 by each cutworm be estimated at only one cent. Toads also 

 feed upon slugs and other garden pests. 



Birds eat Insects. The food of birds makes them of the 

 greatest economic importance to our country. This is because 

 of the relation of insects to agriculture. A large part of the diet 

 of most of our native birds includes insects harmful to vegetation. 

 Investigations undertaken by the United States Department of 



HUNTER, CIV. BI. 14 



The common toad, an insect eater. 



