They are lengthy and slender. They have a boomerang-shaped cranium and a noxious mucus coating. They have been lurking in plain sight in the United States for years.
They can secrete the neurotoxin tetrodotoxin, which is also found in pufferfish and blue-ringed octopuses. Some species are shorter than an inch (2.5 centimeters), while others can grow up to 15 inches (38 centimeters) in length. Each fragment will regenerate into a complete worm if it is cut up.
With recent sightings of hammerheads in Washington, D.C., New Yorkers and others in the Northeast Corridor may ponder how long it will be before the toxic intruders move further north.
According to Peter Ducey, a professor of biological sciences at the State University of New York at Cortland, the worms have been present in New York state for decades (and likely in a much larger portion of the country than we suspect).
“These animals are widespread in New York,” Ducey. They are ubiquitous and abundant.
Climate change is bringing milder temperatures and more precipitation to the Northeast, allowing southern populations to expand northward, but “we don’t yet have enough data to tell,” Ducey said.
The news and social media tend to favor tales about “unusual or scary creatures,” according to Ducey, and these worms and their potential impact on surrounding ecosystems “are certainly uncommon.” Observe, but do not contact
Hammerhead worms are a species of planarian, or flatworm. In North America, four species of the genus Bipalium and one species of the genus Diversibipalium of invasive hammerhead worms have become established, according to Bruce Snyder, associate professor of biology at Georgia College and State University. According to the National Invasive Species Information Center of the United States Department of Agriculture, the worms are believed to have arrived in the United States in 1891 through landscaping materials.
The preponderance of hammerhead worms (also known as broadhead planarians) are currently found in the southeastern United States, where they prefer moderate, moist environments.
Snyder explains, “They are frequently found in forests, but are also associated with human development.”
Since the worms tend to wind up wherever soil is transported, “they’re in a lot of gardens, yards, and around houses,” he said. In these habitats, they are found in leaf debris. You frequently discover them beneath rocks, logs, or garbage.”
More than 3,000 sightings of the invasive hammerhead species Bipalium kewense in southeastern states have been submitted to the iNaturalist database by citizen scientists. According to the Maine Department of Agriculture, Conservation, and Forestry, the worms are also present in California and Oregon, and there have been reports of sightings in southern and central Maine since 2022.
According to the New Jersey Department of Environmental Protection, hammerhead tetrodotoxin, which disrupts neuronal signaling to muscles, can make pets ill if they consume the worms. Ducey warned that direct contact with the worms can cause skin irritation in humans, but the effects may be more severe if the toxins reach the body via a wound.
“My students and I wear gloves when handling worms in my laboratory,” he said. In general, we attempt to interact with them as little as feasible.
According to the New Jersey Department of Environmental Protection, hammerheads feed on earthworms, mollusks, and invertebrates, and may use their venom to subdue prey or deter predators.
Ducey began studying nematodes in the 1990s, but hammerhead sharks arrived in New York decades earlier; he remembers seeing them in his Long Island backyard as a child.
Bipalium adventitium was discovered in the New York area for the first time in 1947 by zoologist Libbie Hyman, who published her discovery in 1954 in the journal American Museum Novitates. She found the worms in a garden in Westchester County, New York, approximately 35 miles north of New York City.
In 1943, Hyman also identified B. adventitium worms in California, which “demonstrated that the worm was already widely distributed across the country,” according to Ducey.
Nevertheless, after Hyman’s discovery, “nobody looked for them very much,” he added.
Prior to approximately 25 years ago, Ducey and students in his lab went in pursuit of the two most widely distributed species in the United States: B. adventitium and B. kewense. The scientists discovered the worms virtually everywhere they searched, even in areas where hammerheads had not previously been reported.
And once such invasive species reproduce successfully in the environment, they are here to stay, according to Ducey.
“The time to acquire them is prior to their arrival in a new location. “The time to stop them is at the very start of these invasions,” he said. Very few invasive species can be eradicated entirely once they have become established.