August, ’18] 
CAFFREY: HEMILEUCA URTICATING SPINES 
363 
NOTES ON THE POISONOUS URTICATING SPINES OF 
HEMILEUCA OLIVLE LARVAE 1 
By D. J. Caffrey, Scientific Assistant, Cereal and Forage Insect Investigations, 
Bureau of Entomology 
Introduction 
While making a preliminary study on the New Mexico range*cat- 
erpillar (Hemileuca olivice Ckll.), Mr. C. N. Ainslie 2 noted that the 
larvae were clothed with urticating spines, apparently as a means of 
protection against some of their natural enemies. Since his observa¬ 
tions were made and during the course of further work on the control 
of this caterpillar, some interesting and important points have been 
observed concerning the poisonous effects of these spines borne by the 
larvae of this species. 
Location and Dispersion of Spines 
The urticating spines are borne in clusters along the subdorsal por¬ 
tion of segments 3 and 4 (mesothorax and metathorax) in the second 
and third instars, and in clusters along the sub-dorsal, lateral and sub- 
ventral portions of segments 2 to 12 in the remaining instars. Al¬ 
though the spines are first developed in the second instar, their pres¬ 
ence is not particularly noticeable until the fourth instar is reached. 
During the fourth and succeeding instars, it is very difficult for a sus¬ 
ceptible person to come into contact with the larvae without becoming 
painfully injured. The same is true of the pupae and cocoons, as the 
urticating spines from the last moulted skin of the larvae apparently 
are caught in the silken threads of the cocoon during the process of 
pupation, thus rendering these objects almost as difficult to handle 
as the larvae. 
Accumulative Nature of the Poisonous Agent 
A notable fact, concerning the poisonous substance contained in the 
urticating spines, was that during the first season, the large H. olivice 
larvae could be handled with safety by most persons starting in to work 
with the species. After a short time, however, and generally during 
the second summer of work, it became impossible for these same per¬ 
sons to handle H. olivice larvae, which had advanced beyond the fourth 
instar, without the protection of gloves. It was a common occurrence 
for the new men to ridicule the more experienced workers for wearing 
Published by permission of the Secretary of Agriculture. 
2 Ainslie, C. N., U. S. Dept, of Agr., Bureau of Ent., Bulletin 85, Part V—The 
New Mexico Range Caterpillar—pp. 76-77. 
