Starr County Butterflies
First instar
Second instar
Typical resting positions and feeding damage. The two upper (out-of-focus) caterpillars are molting to L3.
Third instar
Fourth instar
Final instar
Pupa
Fresh Rawson's Metalmark, dorsal view
Fresh Rawson's Metalmark, ventral view
Rawson's Metalmarks are extremely rare in the Rio Grande Valley of Texas, and extremely difficult to distinguish from our more common Fatal and Rounded Metalmarks. I have yet to find a metalmark I am confident is Rawson's. So I was grateful and delighted when Bill Dempwolf offered to send me some eggs he had obtained from a female in the Austin area.
I somehow lost the pictures of the eggs, but they look like other Calephelis metalmarks: think of a wheelbarrow tire with pentagonal and hexagonal treads, or look at a Rounded Metalmark picture here.
Roy Kendall back in the 1970s reported the typical host plant for this species to be Ageratina havanensis (common names include Shrubby Boneset and Havana snakeroot). It is not found in this area, but he also reported that the metalmarks use Conoclinium greggii (Gregg's Mistflower), which was available. I therefore reared the caterpillars on the latter host.
If I did not make a mistake in observation, these caterpillars underwent 5 instars, whereas in my previous experiences with Calephelis metalmarks I only observed four. The early instars were not cryptic but were very inconspicuous when they rested between leaf ribs (see third picture). The prepupal caterpillar does not spin a cocoon, but the hairs (setae) that are left behind when it pupates give that impression and probably offer some level of protection.
This study took place in May, 2022. The first adult emerged exactly 3 weeks after the first egg eclosed, so the entire life history probably takes about 4 weeks.