By JAVIER GONZALEZ
Information for this column was sourced from butterfliesofamerica.com/docs/Junonia-syen.12428.pdf.
Though Monarch migration is mainly over, there is still a chance to see them and a few other butterfly species fluttering around South Padre Island during the winter months. This is mainly due to the evergreen
nature of their caterpillar food plants (host plants) in our subtropical coastal climate. Two species of which have recently become “special” to the Laguna Madre area thanks to a reclassification of the “Buckeye”
butterfly complex urged by the revelations of modern DNA genome sequencing!
Findings presented by biochemist researchers in a 2020 paper published in the scientific journal, Systematic Entomology, titled Speciation in North American Junonia from a Genomic Perspective finally set order to
the famously confusing genus and the distribution of its species. For decades it was thought that only two Buckeye butterfly species were present in the RGV, the Common Buckeye (Junonia coenia) which has a wide
range across most of the United States, and the ‘Dark’ Tropical Buckeye (Junonia genoveva nigrosuffusa), which is a bit smaller, darker in coloration, and has a more tropical distribution with the northern end of its
range extending into the US in southern Arizona, New Mexico, the Trans-Pecos and the southern coastal tip of Texas.
Here, in the Laguna Madre area though, there was one that didn’t quite fit the mold of either of the two species. It was larger, brighter, and had some other subtle differences that one couldn’t exactly pinpoint, but
made you feel it was something else. Some speculated it could be the Mangrove Buckeye (Junonia evarete) or the Tropical Buckeye (Junonia genoveva), both ranging along the Florida coast, with the latter only in the
southern tip of Florida. Mangrove Buckeye made sense since the Laguna Madre has large stands of Black Mangrove (Avicennia germinans), the Mangrove Buckeye’s host plant. But even then, Black Mangrove has just recently been experiencing a range expansion northward during the last couple of decades as the climate warms. It is now abundant along the shores of the Lower Laguna Madre when not too long ago it was mainly found along the mouth of the Rio Grande River and South Bay.
DNA samples of all the buckeye species mentioned were collected and after their genomes were sequenced and compared, some very surprising results were discovered. The Common Buckeye remained as a constant
in our area, but the larger and brighter one found along the coast was not a Common Buckeye variation, but it also wasn’t Mangrove Buckeye (J. genoveva) or Tropical Buckeye (J. evarete). Discoveries concluded that
the Mangrove Buckeye and Tropical Buckeye were actually not found in the US at all, with their ranges confined to Central and South America. The large and bright coastal buckeyes of Texas and Florida were now a new species, the West Indian Mangrove Buckeye (Junonia neildi) with the South Texas population being a subspecies (Junonia neildi varia) whose range extends all the way south to the Yucatan Peninsula of Mexico.
This subspecies is now a specialty butterfly for the Laguna Madre area! It can be seen along the boardwalk at South Padre Island Birding Nature Center & Alligator Sanctuary year-round as the Black Mangroves
foliage stays fresh even through the winter.
The “Dark” Tropical Buckeye (J. genoveva nigrosuffusa) was also not what it was thought to be. Results concluded that it was its own species and was renamed to Dark Buckeye (Junonia nigrosuffusa) but it didn’t
occur in the RGV! Its range in the US remained southwestern, but its eastern edge only reached the Trans-Pecos in Texas. The dark coastal buckeye of South Texas turned out to also be its own species; new to science!
This new species was given the name Twintip Buckeye (Junonia stemosa). The caterpillar feeds on Woolly Stemodia (Stemodia tomentosa), which is a sprawling, light gray, perennial plant of sandy soils. Big mats of
it can be found on SPI on vacant lots and roadsides. Twintip Buckeye caterpillars have special adaptations that allow it to feed on the wooly foliage, which Common Buckeyes cannot do.
It is possible to see all three Buckeye butterflies of the RGV; Common Buckeye, West Indian Mangrove Buckeye, and Twintip Buckeye in the same field in the Laguna Madre area, especially during the spring and
fall seasons. During the winter through, you are more likely to see the two new ones since the Agalinis host plants to the Common Buckeye are annuals that mostly die off during the winter. Look for them during
sunny days on patches of Betonyleaf Mistlfower (Conoclinium betonicifolium) along the coast and South Padre Island.