Hammerhead worms are predatory land flatworms, recognized by their distinctive spade- or hammer-shaped head. Not native to many regions where they are now found, they are a species of concern.
Origins of Hammerhead Worms
Hammerhead worms originate from the warm, humid regions of Southeast Asia, including areas like Vietnam. Their native habitats feature moist conditions with abundant organic matter, such as leaf litter and rich soil, which support their survival.
How Hammerhead Worms Spread Globally
The global spread of hammerhead worms primarily occurs through human activities. They are often transported unintentionally within the soil of potted plants, nursery stock, and other horticultural materials. Their resilient, difficult-to-detect egg cases aid their movement across continents. Once introduced, their asexual reproduction, including regeneration from small segments, allows them to establish populations quickly.
Current Distribution
Hammerhead worms are established as invasive species across various parts of the world. In North America, they are widely present, particularly throughout the Southern and Eastern United States, with sightings in states including Alabama, California, Florida, Georgia, Louisiana, Mississippi, North Carolina, South Carolina, and Texas. They are also found in greenhouses and outdoor environments in more northern states like Illinois, Kentucky, Massachusetts, Michigan, New Jersey, New York, and Ohio, and have recently been noted in regions such as Washington D.C., Virginia, Maine, Arkansas, and North Texas.
Beyond the U.S., they are documented in Canada, with reports from Ontario since at least 2017. In Europe, hammerhead worms are widespread, particularly in France and Italy. Their presence extends to French overseas territories, including Caribbean islands and French Guiana.
These worms prefer moist habitats such as gardens, flower beds, and areas with leaf litter or wet mulch. They often seek shelter under rocks, logs, and shrubs, but can be observed on surfaces like driveways and sidewalks after heavy rains.
What to Do If You Encounter One
If you find a hammerhead worm, it is important to handle it carefully. Wear gloves or use an implement like tongs to avoid direct skin contact, as some species secrete a neurotoxin that can cause irritation. Do not attempt to cut the worm, as its remarkable regenerative abilities mean that each segment can grow into a new worm, effectively multiplying the problem.
To dispose of a hammerhead worm, place it in a sealed container or bag. Effective methods include applying table salt, white vinegar, or rubbing alcohol directly to the worm within the sealed container. Alternatively, submerging the worm in soapy water or placing the sealed container in a freezer for 24 to 48 hours can also be effective.
After handling, always wash your hands thoroughly. Reporting sightings to local cooperative extension services or invasive species networks, such as iNaturalist or state-specific invasive species institutes, can help track their spread.