316 



Handbook of Nature-Study 





Black swallow-tail caterpillars, showing 



two stages of growth. The larger 



one has the scent organs protruded. 



Photo by M. V. Slingerland. 



four pairs ot prolegs and the hind 

 prop-leg, all of which enable him 

 to hold fast to the stem or the leaf; 

 these fat legs are green, each 

 ornamented with a black, velvety 

 polka-dot. 



When we were children we spent 

 hours poking these interesting 

 creatures with straws to see them 

 push forth their brilliant orange 

 horns. We knew this was an act 

 of resentment, but we did not 

 realize that from these horns was 

 exhaled the nauseating odor of 

 caraway which greeted our nostrils. 

 We incidentally discovered that 

 they did not waste this odor upon 

 each other, for once we saw two of 

 the full-grown caterpillars meet on 

 a caraway stem. Neither seemed 

 to know that the other was there 

 until they touched ; then both drew 

 back the head and butted each 

 other like billy-goats, Whack! 

 whack! Then both turned labor- 

 iously around and hurried off in a 

 panic. 



The scent organs of these caterpillars are really little Y-shaped pockets 

 in the segment back of the head, pockets full of this peculiar caterpillar 

 perfume. Under the stimulus of attack, the pocket is turned wrong side 

 out and pushed far out making the "horns," and at the same time throw- 

 ing the strong odor upon the air. This spoils the flavor of these cater- 

 pillars as bird food, so they live on in serene peace, never hiding under 

 the leaves but trusting, like the skunk, to a peculiar power of repelling 

 the enemy. 



We must admire this caterpillar for the methodical way in which it 

 eats the leaf: Beginning near the base, it does not burn its bridges 

 behind it by eating through the midrib, but eats everything down to the 

 midrib; after it arrives at the tip of the leaf it finishes midrib and all on 

 its return journey, doing a clean job, and finishing everything as it moves 

 along. (See Moths and Butterflies, Dickerson, p. 42.) 



When the caterpillar has completed its growth, it is two inches long; 

 it then seeks some sheltered spot, the lower edge of a clapboard or fence 

 rail being a favorite place ; it there spins a button of silk which it grasps 

 firmly with its hind prop-leg, and then, with head up, or perhaps 

 horizontal, it spins a strong loop or halter of silk, fastening each end 

 of it firmly to the object on which it rests. It thrusts its head 

 through, so that the halter acts as a sling holding the insect from falling. 

 There it sheds its last caterpillar skin, which shrinks back around the 

 button, revealing the chrysalis which is angular with ear-like projections 

 in front. Then comes the critical moment, for the chrysalis lets go 

 of the button with its caterpillar feet, and trusting to the sling for 



