22 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



IV PROTECTIVE ARMATURE BOTH IN SHAPE AND COLOR AND 



DEFENSIVE MOVEMENTS. 



Referring to the aggressive or defensive movements of the caterpillars of Adelocephala, 

 Dr. Jewett remarks: " L'p to the third molt the larva? when alarmed move the pr<)tul)erances 

 on the second and third segments as if to frighten away the intruder." 



In my Notes (p. 150) I remark regarding them in the second stage: "In this stage upon 

 touching or teasing the larva the tlioracic spines spring out; at the same time the head, together 

 witli the thoracic region, jerk violentlv. as if to beat oft' an intruder. Also, when two caterpillars 

 meet they evidentlj^ attack each other, butting and striking with their horns like two hostile goats, 

 deer, or cattle. It seemed evident, after repeated observations, that the great thoracic spines are 

 of real defensive use." Again, in referring to a larva in the fourth stage: ""it would appear 

 probable that the formidable spines of the grown-up caterpillar save it not infrequently from 

 being swallowed by birds, though the horns are probably of greater use in the earlier stages, 

 when they are much longer and much more movable, in frightening awa}' ichneumons and 

 Tachinffi. For example, even when 20 mm. in length, a larva was seen when teased to spread 

 apart its great arm-like horns, while the full-fed ones did not notice such stimidus." 



It was also added that in the larva' of the last stage, instead of being green as in the earlier 

 stages, they become i"oseate pale coral red, and " not so near in tint to the spines of the food 

 plant as in the young. "When the caterpillar is at rest they are held close together in a recurved 

 position, and in the grown-up larva when touched they are not moved or the body jerked in 

 response to such stimulus." 



"The horns in Sphingicampa are not held spread out as in C. regal i-i, but those of each pair 

 are constantly held close to each other. The horns and the six silver}', opalescent, shining tuber- 

 cles probablj" become terrifying by the movements of the larva. The latter are turned on and 

 throw their light out suddenly like flashes, and may thus have a deterrent effect on their 

 enemies." (Proc. Amer. Phil. Soc, XXXI, p. 157.) 



It is worthy of note that the larvfe of most of the species of this genus feed on spiny plants, 

 one, A. liiriihii\ on the spiny or honey locust. 



In Brazil, according to Peters, .1. vardii lives on a spiny mimosa whose leaves on the under- 

 side are violet brown: ^4. suhavgnlata lives on a spiny climbing plant, A. hrevis on a thorny 

 mimosa in the gardens of Rio Janeiro, and the caterpillars of an undescribed species on an 

 acacia. 



These caterpillars, with their remarkably long spines, including those figured by Peters and 

 by Burmeister, have the dorsal spines of the abdominal segments nearly or quite as long as those 

 on the thoracic segments. As these larva? are quite large, and their spines in some cases from a 

 half to an entire centimeter in length, they would easih* be mistaken by birds and lizards, as 

 well as monkeys and other mannnals. for the smaller spines of the trees or shrubs on w^hich they 

 feed, especially when not in motion, and it is a question whether they are not more useful as 

 mimicking the spines of their food plants than as simplj' defensive structures. Yet a l)ird, or 

 even a lizard, might hesitate before swallowing such spinose creatures. 



As to the origin of these great spines and their adaptation as protective structures it is not 

 easy to frame a hypothesis. To suppose that thej^ arose by natural selection is scarcely an ade- 

 quate explanation, though this may account for their preservation after they have once been 

 developed. 



V. COLORATION IN THE LARV.(E OF THE CERATOCAMPIN.^. 



We will begin with the species of Anisota. in which the armature, owing to the reduction of 

 all l>ut the pair of slender thoracic horns, is reduced, and becomes subordinate to the coloration. 

 This is especially seen in A. ticruitorla where the alternating deep ocherous and black-brown bands 

 are so prominent, the effect of the black spines in most cases being lost, owing to the position 

 of those of the dorsal and subdorsal series in the dark brown or tdackish stripes. 



