RIO GRANDE CITY, Texas— Following a lawsuit by the Center for Biological Diversity, the U.S. Fish and Wildlife Service today proposed to protect the prostrate milkweed as endangered. Just 24 populations of the plant survive in South Texas and northern Mexico, where they serve up large quantities of nectar to bees and tarantula hawks.
The Service also proposed to designate 691 acres in eight units in Zapata and Starr counties, Texas, as critical habitat for the plant.
“I’m hopeful that Endangered Species Act protection will keep the prostrate milkweed flowering in South Texas for generations to come,” said Michael Robinson at the Center. “This fascinating plant long ago secured a sunny niche in tough landscapes, but it’s being driven to the edge of extinction by human development. Federal action is crucial.”
The prostrate milkweed is imperiled largely because of competition from nonnative buffelgrass, which is planted as livestock forage and displaces native plants. Moreover, plowing to facilitate conversion of savannahs to buffelgrass pasture destroys the underground tubers of the prostrate milkweed.
Construction and maintenance for roads, utilities and the oil and gas industry also destroy these plants, and additional border wall construction on the Lower Rio Grande National Wildlife Refuge threatens to uproot more of them.
Under natural conditions, the prostrate milkweed is thought to be able to persist at low densities because it produces so much nectar that far-flying pollinating insects such as tarantula hawks and large bees are so juiced up after visiting it that they can fly farther and pollinate other, relatively distant prostrate milkweed populations. But as prostrate milkweed numbers and densities have declined, the plant is also imperiled by lower reproductive success and loss of genetic diversity.
Just 24 populations of prostrate milkweed remain in Starr and Zapata counties in Texas and in Tamaulipas and eastern Nuevo León in Mexico. Nineteen of those populations are rated in low condition, the remaining five are in moderate condition and none are in high condition — indicating acute imperilment.
The Endangered Species Act has been successful in keeping more than 99% of species under its wing from going extinct. But long delays in adding animal and plant species to the endangered list have heightened the perils and made recovery more difficult.
Critical habitat areas are protected from federal actions and funding that would destroy or harm them. Species for which critical habitat have been designated are twice as likely to be trending toward recovery than those without.
The Fish and Wildlife Service’s proposed rule comes in response to a Center lawsuit. The suit sought to force the agency to make timely evaluations and protection decisions for 241 plant and animal species thought to be trending toward extinction, including the prostrate milkweed and more than 35 others in Texas. The prostrate milkweed was the subject of a 2007 protection petition by WildEarth Guardians.
The proposed rule starts a 60-day public comment period. The Fish and Wildlife Service must make a final listing and critical habitat decision within a year.
“The prostrate milkweed keeps a low profile and isn’t showy, but it’s been part of the South Texas grasslands and shrublands since time immemorial,” said Robinson. “I’m glad it’ll soon get help to survive and continue supporting pollinating bees and wasps, whose numbers are also declining.”
The prostrate milkweed’s low and sprawling leaves and stem wilt during droughts. But the plant’s subterranean tuber stays alive and, after soaking up moisture from occasional tropical storms, sends up stalks and pink and yellow flowers.