Want to Meet the Beetles? Better Hurry, Removal of Milkweed Beetles from San Antonio River’s Milkweed Patch Imminent

An invasion of red-and-black milkweed beetles have made a temporary eyesore of the San Antonio River’s celebrated Milkweed Patch on the Museum Reach.  The striking insects, whose colorful torsos suggest the patterns of a tiki mask, have moved into the 1200-square foot Tropical milkweed garden on the banks of the San Antonio River just south of the Pearl Brewery  in a classic play of nature’s cycles.

Milkweed Beetles have taken over the Milkweed Patch

The beetles, which look like ladybugs on steroids, don’t bite, sting or carry diseases. They do, however, defoliate milkweed plants, and have left the highly trafficked stretch of the River with some unattractive bald spots.

Migrating Monarch butterflies moved through town earlier this spring, laying the first generation of eggs in their annual migration at the Milkweed Patch.  The resulting acrobatic caterpillars occupied the Patch, feasting on milkweed leaves, the Monarch butterfly host plant.  Late straggling Monarchs continue to mingle with our local colony but the pervasive milkweed beetle, Labidomera clivicollis, dominates.

Milkweed Patch going bald thanks to milkweed beetles

Volunteers for the Monarch Larvae Monitoring Project (MLMP), a citizen scientist program based at the University of Minnesota and which aims to better understand the Monarch life cycle and migration, have noticed fewer Monarch caterpillars and chrysalises during their weekly observations as beetles consume the milkweed leaves.
Discussions ensued about possibly pruning the milkweeds, which typically die back in winters when a hard freeze occurs.   That didn’t happen this year.  But San Antonio River Authority staff determined a better approach would be to hand-remove the beetles, THEN prune the plants.

Milkweed beetles have defoliated the Milkweed Patch. But aren’t they cute?

“We believe this to be a holistic management approach with minimal negative impact to the environment that is consistent with our commitment to the local community for the project, ” said Steven Schauer, Manager of External Communications at the San Antonio River Authority (SARA), which oversees maintenance of the area.   The Museum Reach stretch of the San Antonio River was designed as a manicured, urban park setting, unlike the Mission Reach section, which is managed as a native riparian restoration.
SARA deserves praise for working with MLMP  volunteers and resisting the use of pesticides to address the problem.   A round of pesticides would quickly rid the area of

Gulf Fritillary, photo courtesy NABA.org

beetles (and other plant pests) and would also jeopardize the Monarchs’ and other butterflies’ continued colonization of the River.  Just north of the Milkweed Patch is a huge Passionflower planting, where Gulf Fritillary butterflies have made their home and are breeding.
If you’d like to “meet the beetles,”  better do so in the next few days.  The critters will be less visible once the hand removal is accomplished.