Starr County Butterflies
Ova
Neonates
First instar
Second instar
Third instar
Fourth instar
Fifth instar
Sixth instar
Pupa
Fresh male Mexican Crescent, dorsal view
Fresh male Mexican Crescent, ventral view
Mexican Crescents began appearing in numbers in the Lower Rio Grande Valley in 2024. Richard Boscoe determined that they were using Tridax procumbens as their host. This plant is considered an invasive species that only arrived in the LRGV at the end of the last century; it has now spread widely throughout the area. It seems likely the butterfly is following the spread of its host.
I reared the species three times in just under a year. Richard Boscoe provided eggs for the first rearing; I confined a female for the second, and I found emerging eggs for the third. Each cohort was observed to have 6 instars, which is unexpected as other Crescents I have reared have pupated after 5 instars. In the final stage the caterpillar seemed to thicken more than lengthen. The coloration of the winter (first two) cohorts was much darker than the last (September), presumably due to temperature.
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Crescent caterpillars superficially all look very similar. The face and the use of Tridax are the best indicators to confirm the identity of a caterpillar.
The September rearing took less than a month; the others a week to two weeks longer. Every reared individual with a plain hind wing on the underside was male, but there were some males with a patterned hind wing.