THE NEW MEXICO RANGE CATERPILLAR. 75 



from side to side sharply, supporting the weight on the rear legs, 

 the head and thoracic legs being drawn beneath the curve of the 

 arched body. 



In the more mature instars, particularly the fifth, they lose some 

 of their fear, and will sometimes eat quietly while being examined 

 under a lens. 



MOLTING. 



When ready to molt the larva ascends a suitable stem, preferably 

 the dead stem of a weed, and hangs head downward until the skin 

 has been shed. Previous to suspension it usually, though not always, 

 spins a light coating of silk upon the stem, and the hooklets of the 

 posterior prop-feet are firmly attached to this web during the process 

 of molting. The attitude assumed is like an inverted interrogation 

 point, the head being drawn under the outcurved body. 



If disturbed during the earlier stages of the operation the larva 

 will manifest its annoyance by repeated quick jerks of the body 

 from side to side, but no abuse however persistent will force it to 

 abandon its hold on the silk when once established. 



The character of the weather is an important factor at this critical 

 period of the larval life, and a cloudy or stormy day or two will mate- 

 rially delay the molting. Larvae have been seen to hang for several 

 days waiting for favorable conditions, but molting usually takes 

 place within an hour or two. The larva suspends itself in the early 

 morning, or the previous evening, and before noon the skin is shed 

 and the newly emerged caterpillar is drying in the sunshine. 



The first noticeable step in the molting process is the inflation of 

 the first thoracic segment, by which the head is thrust forward and 

 the spines, that normally droop cephalad, stand stiffly erect. The 

 segment is twice its usual length at this time. 



After hanging motionless for some time, except for slight move- 

 ments of the muscles, a regular rhythm is to be noticed, waves of 

 motion that come slowly down the body to the head. As these pul- 

 sations continue, the thoracic region gradually inflates, and the larval 

 skin separates from the body, until after fifteen or more waves, fol- 

 lowing each other at intervals of ten seconds, the paperiike skin 

 opens along the side of the thorax and one gets the flash of fresh yel- 

 low rosettes of bristles emerging through the rent. The head is at 

 once withdrawn, and in a few seconds the larva moves away, brave 

 in its panoply of glittering yellow spines, which in the course of 

 twenty-four hours turn dark. The face plate of the cast skin some- 

 times adheres and remains with the skin, but more often is pushed 

 loose and falls to earth. 



During the drying period, after emergence, the fresh larva has 

 often been seen to bend its head back over the body and roll the two 



