Insecta. 51 



(cow sheds). In some forms the masters are so dependent upon their 

 slaves that they perish unless cared for by them. Some of the ants that 

 keep the plant lice as cows are injurious through the action of the plant 

 lice, which feed on the roots of corn and other plants. The ants carry 

 the plant lice, or their eggs, into holes in the ground where they survive 

 the winter, which they probably would not otherwise be able to do. 

 Yellow ants often invade houses, making a nest within a wall where it 

 is almost impossible to dislodge them; these are often called "red 

 ants." Though fond of sweets, ants are almost omnivorous. 



Other Hymenoptera. Among the other Hymenoptera we may notice 

 the sawflies whose leaf-eating larvae are known as the rose slug, pear 

 tree slug, currant worm, etc. Various forms of Hymenoptera sting their 

 eggs into the stems and leaves of plants. Around the egg is formed a 



FIG. 37. LARVA OF A HAWK MOTH, WITH COCOONS OF A PARASITIC ICH- 

 NEUMON FLY. 



From Kellogg's Zoology. 



swelling known as a gall. In this the larva develops, finally eating its 

 way out. There are many kinds of galls, and the entomologist knows 

 the kind of insect from the characteristic form of the gall, and the adult 

 insects are known as "gallflies.'" 



The ichneumon flies have an ovipositor consisting of long, slender 

 (usually three) threads, by means of which the eggs are deposited, 

 usually in the trunks of trees, where these larvae prey on the larvae of 

 other boring insects. 



In the fall one occasionally sees a sluggish caterpillar covered with 

 little oval bodies resembling eggs ; examined more closely, these little 

 bodies are seen to have a silky finish ; they are the cocoons of a para- 



