OF WASHINGTON. 131 



joints, and, as if designedly to make the resemblance more decep 

 tive, the top egg is rounded and slipped a little to one side, form 

 ing a most perfect head with projecting jaws. When the forming 

 embryos begin to darken in color, and are seen through the trans 

 parent shells, then the mimic worm becomes truly life-like, with 

 mottled segments and a black head. The egg-stick is always 

 attached to the true leaves or to the spines of Opuntia. They are 

 straw-colored when fresh laid. Forty-five or fifty eggs may be 

 counted in a single stick, but the moth frequently deposits short 

 sticks consisting of a few eggs only. I have seen occasionally 

 four or five eggs laid in a short stick, and in that case the cater 

 pillar-like head is not apparent and the moth probably left the 

 work unfinished because of some disturbance during the opera 

 tion. As the various species of Opuntia vary much in the length 

 of their spines and true leaves, these unfinished sticks often escape 

 notice among the spines of the long-leaved species, and this re 

 semblance to the spines and spiny leaves of the plant may have 

 been the original raison d'etre of the mimicry, which has, how 

 ever, been elaborated by the moth in her finished work, on our 

 short-spined Opuntias at least, and has at last produced a mim 

 icry of a mimicry by copying a mimicking caterpillar. 



The eggs are laid at night, and the operation of depositing them 

 has not been observed. It must, however, be a wonderfully in 

 teresting performance. The egg-stick shown in the drawing is 

 So mm. long. The separate eggs are cylindrical and measure 2 

 mm. in length by 7 mm. in width. The surface is beautifully 

 reticulated with wavy raised lines anastomosing obliquely. The 

 eggs are cemented together with a brownish glue which, under 

 the pressure exerted upon the mass, is squeezed out at the sutures 

 between each two eggs in the stick and hardens there, forming a 

 ring or collar which always adheres to the egg beneath when two 

 eggs in the stick are separated. It sometimes has the appearance 

 of a circle of spinules, owing to the corrugations of the surface 

 upon which it is moulded. 



The young larvae of Melitara prodenialis, on hatching from 

 the eggs, feed for a time externally upon the bud-like leaves of 

 Opuntia. When they become larger and stronger they cut 

 through the silicious skin of the pads. The wounds made by 

 them in the plant exude a gummy liquid, and a scab-like crust is 

 formed. Under this the larvae live in companies, large or small, 

 according to the size of the plant, until they are about one-third 

 grown. After this they burrow deeply into the substance of the 

 succulent stems. The larvas, as long as they live upon or near 

 the exterior of the plant, are light brown in color, but after they 

 burrow into the pulp and approach their full size, they attain a 



