234 ZOOLOGY 



leaves; they are tiny sugarloaf-shaped dots a twentieth of an 

 inch in length. Some wonderful instinct leads the animal to 

 deposit the eggs on the milkweed, for the young feed upon no 

 other plant. Eggs laid in May hatch out in four or five days 

 into rapid-growing caterpillars, each of which will molt several 

 times before it becomes full size. The animal at this stage is 

 known as a larva} 



The Caterpillar. — Field Work. The monarch caterpillar has its body 

 covered in a banded combination of yellow and green. Note the horns that 

 are sometimes protruded from the head. Notice where you find the ani- 

 mals; is their color a protection? The caterpillar is very unpleasant to 

 the taste; by means of its conspicuous color the animal warns birds that 

 it is not good to eat. This is known as warning coloration. 



The body of the caterpillar is segmented and provided with several pairs 

 of legs. Notice that the number of segments is the same as in the adult 

 butterfly. The true or butterfly legs are found on the anterior segments of 

 the body. Compare them with the false legs or prolegs found more pos- 

 teriorly. Notice the tips of the legs. How are the legs adapted to cling- 

 ing? How are the true legs used when the caterpillar is feeding? Watch 

 the caterpillar when it is feeding; the mouth parts are very different from 

 the adult. It is at this stage that caterpillars are of considerable economic 

 importance because of the damage they do to trees and other green plants. 



Formation of Pupa. — After a life of a few weeks at most, the 

 caterpillar stops eating and begins to spin a tiny mat of silk upon 

 a leaf or stem. It attaches itself to this web by the posterior 

 pair of prolegs, and there hangs until a last molt (which occurs 

 within twenty-four hours after attachment) gives the animal the 

 form it assumes in the stage known as the chrysalis or pupa. 



The Pupa. — Field work. The chrysalis of the monarch is green in color 

 with gold spots. It may be found upon almost any green plant, fence, or 

 even stone, as the animal leaves its food plant before going into this stage. 

 If you find one, examine it carefully. Make out the three parts of the body; 

 the wings, antennae, and legs may be seen closely folded against the body. 

 The spiracles also show plainly. 



The Adult. — After a week or more of inactivity the exoskeleton 

 is split along the dorsal side, and the adult butterfly emerges. At 

 first the wings are soft and much smaller than in the adult. Within 

 fifteen minutes to half an hour after the butterfly emerges, how- 

 ever, the wings are full sized, having been pumped full of blood. 



In the adult form the animal may survive the winter. The 

 milkweed butterfly is a strong flyer, and has been found over five 



* For laboratory work see Hu^te^ and Valentine, Manual, page 107. 



