Invasive worm spotted in San Antonio area could carry rat lungworm parasite

New Guinea flatworm is a new invasive species in Texas, expert says

The New Guinea flatworm has been spotted throughout San Antonio, Corpus Christi, Austin, College Station and the greater Houston area. These photos were taken in a suburb of San Antonio in July, 2020. (KSAT)

SAN ANTONIO – An invasive flatworm has made its way into Texas and has been found throughout the San Antonio area, experts say.

In fact, this writer spotted some last weekend.

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I remembered reading about an invasive type of worm, and when my preschooler pointed out the unusual black worms on our back porch after a rain storm, I knew they weren’t typical earthworms. So I reached out to The Texas Invasive Species Institute and sent some pictures for confirmation.

“This is the New Guinea flatworm (Platydemus manokwari) which is a fairly recent invader in Texas,” I was told.

The New Guinea flatworm may be tiny, but it can carry a dangerous parasite.

According to the Texas Invasive Species Institute, the tiny black worms made their way into the United States and were first spotted in Florida in 2015. Since then they’ve been seen throughout the Southeastern United States. Here in Texas, they’ve been spotted throughout San Antonio, Corpus Christi, Austin, College Station and the greater Houston area.

The flatworms are predators of native snails and other invertebrates. While they’re not parasites themselves, they have the ability to transmit harmful nematodes (Angiostrongylus cantonensis) to mammals including humans. Angiostrongylus is commonly referred to as rat lungworm.

“The correct host for these nematodes are rats, but they’ll try to get into any mammal- they’re just not able to complete their lifecycle inside other non-rat hosts,” said Ashley Morgan-Olvera, director of research and education/outreach for the Texas Invasive Species Institute.

The parasite is transmitted to mammals when they ingest an infected flatworm or slug.

“For humans in developed countries, it can happen after we handle the flatworm/slug and then touch our mouths. Thankfully, transmission of the parasite is easily prevented. This is why we tell every citizen who contacts us (or looks at the species page on our website) not to bare handle any flatworms and to always wash your hands with soap and water afterward,” Morgan-Olvera said.

People can also get the parasite from unwashed vegetables.

“Simply washing any garden vegetables before consumption would prevent any parasite transmission to humans,” Morgan-Olvera said.

According to the Centers for Disease Control and Prevention, Angiostrongylus usually causes mild symptoms in humans but can lead to a rare type of meningitis (eosinophilic meningitis) with symptoms including headache, stiff neck, tingling or painful feelings in the skin, low-grade fever, nausea and vomiting.

If you spot the New Guinea flatworms in your yard, it’s recommended that you spray them with a mixture of 1 ounce of citrus oil per half-gallon of white vinegar to kill them, and then dispose of them.

You can also place as many as you can fit in a Ziploc bag with a little salt, freeze for 48 hours and throw the bag away, according to TISI, but experts highly discourage handling them with bare hands.

The worms range in size from 1.6 to 2.6 inches. Both ends look similar, but the end with the head is narrower and has two eyespots. The underside of the worm is a pale tan color and the upper-side has a faint stripe.

If you think you found one, but need confirmation about the species, you can send pictures by email to Morgan-Olvera at If you can preserve it in a container with isopropyl or ethanol alcohol like vodka, rum or Everclear, she’s also accepting specimens. Reach out to her for more information on how to do that.

Click here to read more about the New Guinea flatworm on the TISI site.

In addition to the New Guinea flatworm, TISI also warned of another invasive species that can carry rat lungworm -- the Black Velvet Leatherleaf slug. Researchers say the slugs are well-established in the San Antonio area.

The Black Velvet Leatherleaf Slug is an invasive species in Texas and can carry the nematode parasite Angiostrongylus costaricensis that causes abdominal angiostrongyliasis in humans. (Texas Invasive Species Institute)

The hammerhead flatworm, also known as the hammerhead slug is another invasive species in Texas. It’s a known predator of earthworms and may feed on other live organisms.

The hammerhead flatworm, also known as the hammerhead slug is an invasive species in Texas. (Photographer: S. E. Thorpe Source: Wikimedia Commons)


About the Author

Julie Moreno has worked in local television news for more than 25 years. She came to KSAT as a news producer in 2000. After producing thousands of newscasts, she transitioned to the digital team in 2015. She writes on a wide variety of topics from breaking news to trending stories and manages KSAT’s daily digital content strategy.

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