Tharsalea hermes

Hermes Copper

Hermes copper is a rare butterfly closely associated with its sole larval food plant, spiny redberry (Rhamnus crocea), limited to San Diego County and (formerly?) a bit of northwestern Baja. It is considered threatened under the Endangered Species Act. Fire, development, and drought have devastated the former range of this butterfly; of 98 known locations with hermes occurances historically, 72 of them are now either considered "extirpated" or "presumed extirpated" (Federal Register, Vol.86, No.242, pp.72394ff.).

Interestingly, the butterfly's range is smaller than the total range of Rhamnus crocea, suggesting that not all of the plants are suitable for the butterfly. So why does hermes live happily in some patches of spiny redberry while avoiding others? Knowing its habitat requirements is obviously important for an imperilled insect. The answer may have to do with certain secondary compounds in the plants. The amounts of these compounds, which, among other things, tell females a leaf or stem is suitable for egg-laying, can vary from place to place depending on local climatic differences (temperature, rainfall). And according to a great study by Liberty I. Malter*, there do seem to be differences in key secondary compounds corresponding to plants within and outside hermes habitats. More study is needed, but this seems like a promising avenue to me.

What isn't helping the Hermes copper - besides fire, development, drought, and being particular about which spiny redberry plants to use - is its sedentary nature and small population sizes. Eventual extinction would, sadly, not be surprising. Hopefully they can hang on and outlast us humans; they'll probably do better without us.

* See Malter's MS thesis, "Effects of Nitrogen Availability and Climate on Hermes Copper Butterly (Lycaena hermes) Habitat in Southern California," accessed here on 11/15/2023. This work was noticed in the 2020 Federal rule noted above.

Tharsalea hermes - Hermes Copper butterfly
The rare Hermes copper, Tharsalea hermes, taking nectar at California buckwheat near Descanso in San Diego County. June 9, 2013. California buckwheat seems to be their preferred source of nectar.
Tharsalea hermes - Hermes Copper butterfly
Another Hermes copper on the same day. These are really spectacular butterflies, and it was thrilling to see them in person. I'd looked for them several times in past years with no success; today would be different.
Tharsalea hermes - Hermes Copper butterfly
A female showing the dorsal side.
Tharsalea hermes - Hermes Copper butterfly
Another Hermes copper. Thanks to a tip from Mark Walker, I found them mostly around buckwheat plants between 1 and 2 p.m. at a spot near Descanso in San Diego County's back country. A female was taking nectar, and a few males patrolled pathways. The host redberry is throughout this area but they come to nectar for a little while just after mid-day.
Tharsalea hermes - Hermes Copper butterfly
One last shot from a memorable day.
Original description of Tharsalea hermes - Hermes Copper butterfly
William Henry Edwards described this butterfly in 1870 in the journal Transactions of the American Entomological Society.
life cycle of Tharsalea hermes - Hermes Copper butterfly
This is an early description (1935) of this butterfly's life cycle by John Comstock and Charles Dammers, published in the Bulletin of the Southern California Academy of Sciences ("Notes on the Early Stages of Three Butterflies and Six Moths from California," v.34, pp.124ff.).

©Dennis Walker