Invasive hammerhead flatworms and black velvet slugs have been seen in San Antonio after recent rains

Invasive species can cause declines to native species populations

Black velvet slug photo on the left courtesy Annie Villaroman. Hammerhead flatworm photo on the right courtesy Alana Gudopp-Kelly.
Black velvet slug photo on the left courtesy Annie Villaroman. Hammerhead flatworm photo on the right courtesy Alana Gudopp-Kelly. (KSAT 12)

SAN ANTONIO – A number of invasive worms and slugs have been seen in the San Antonio area recently after a few weeks of rainy weather.

Alana Gudopp-Kelly, who lives in Stone Oak, spotted a hammerhead worm climbing a pillar in front of her house in the area behind Reagan High School.

“I read they are invasive so I put it in a bag with salt and alcohol,” Gudopp-Kelly said.

Annie Villaroman captured a photo of a black velvet slug by her North Side house last week and shared it to social media because she thought it was beautiful. Turns out, it’s also an invasive species.

KSAT reached out to Matt McClure with the Texas State University Invasive Species Institute who said that the black velvet slugs have been established in the San Antonio area over the last several years.

McClure also noted that “hammerhead worms have been well-established in Texas for many years, although there may be new invasions of other species of hammerhead worms happening too.”

Invasive species can cause declines to native species through competition for habitat and food or disease and parasitic transmission, among other things.

“Invasive slugs and snails (as well as native ones) can cause damage to garden plants, and hammerhead flatworms are predators to earthworms and other invertebrates,” said McClure.

The only direct danger to humans, he said, is if the worms or slugs are ingested. They might also be eaten by an animal and then that animal might contaminate a surface if they become infected with nematode parasites.

These parasites are known to cause abdominal angiostrongyliasis in humans which has symptoms like fever, abdominal pain and tumor-like lesions, according to Science Direct.

McClure stated that this can occur with other invertebrates as well and encouraged people to always wash their hands after encountering any organisms in general.

“Hammerhead flatworms also release a toxin presumably used to help them catch prey and avoid predators, which can cause irritation when handled,” McClure said.

Another type of invasive worm, the New Guinea flatworm, which can also carry nematode parasites, has also been spotted in the San Antonio area.

The TSU Invasive Species Institute has more information on the black velvet slugs, hammerhead flatworms and New Guinea flatworms on its website.

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About the Author:

Mary Claire Patton has been a journalist with KSAT 12 since 2015. She has reported on several high-profile stories during her career at KSAT and specializes in trending news and things to do around Texas and San Antonio.