Hammerhead worms, scientifically known as Bipalium, are land planarians characterized by their distinctive hammer or half-moon-shaped heads. These predatory flatworms have garnered attention due to their non-native status in many regions, their unique feeding habits, and potential ecological impacts. While they may evoke fear due to their appearance and toxicity, understanding their biology and behavior is key to managing their presence and mitigating any negative consequences.
What are Hammerhead Worms?
Hammerhead worms are land planarians, a type of flatworm belonging to the genus Bipalium. The name "hammerhead worm" comes from the distinctive shape of its head, which resembles a hammer or a half-moon. They are typically light brown or honey-colored, with some species exhibiting dark stripes running down their backs. These worms can grow to be impressively long, with some individuals exceeding 10 inches in length. They are slimy, legless, and predatory.
Identification
The hammerhead shape of the flatworm’s head combined with its long body (up to 1 foot) may cause fear in humans. Drawings of the anterior region of 6 species of the genus Bipalium, showing the differences in shape and color. With the exception of B. nobile, they are invasive species in the United States.
Distribution and Habitat
Native to tropical regions like Southeast Asia, hammerhead worms have been introduced to various parts of the world, including North America and Europe. They were introduced to the United States in 1901 when they were brought over on horticultural plants. They easily hide among objects and in soil where there's moisture, so moving any type of container or plants around the world has allowed them to colonize new areas. As of 2007, four invasive species of Bipalium were known in the United States: B. adventitium, B. kewense, B. pennsylvanicum, and B.
In Kentucky, hammerhead worms have been confirmed in multiple counties, suggesting a wide distribution throughout the state.
Read also: Diet of the Great Hammerhead
These worms thrive in warm, damp environments, often found under rocks and logs, in leaf litter, or in gardens and forests. Hammerhead worms are most likely to be found in warm, damp environments. They might be spotted under rocks and logs or in leaf litter. They are sensitive to light and prefer cool, dark, moist areas.
Diet and Predatory Behavior
One of the primary concerns regarding hammerhead worms is their diet. They are carnivorous predators, feeding on earthworms, snails, slugs, and insects. They are also cannibalistic, sometimes eating their own. These flatworms can track their prey.
To capture prey, hammerhead worms use their body muscles and sticky secretions to attach themselves to the victim, preventing escape. They then evert their pharynges from their mouths, located on the midventral portion of their bodies, and secrete enzymes that begin the digestion of the prey. After digesting their prey into a gooey puddle, the hammerhead worm uses tiny, hairlike structures on its underside, called cilia, to suck in the victim.
Impact on Earthworm Populations
The hammerhead worm has no known natural predators or threats. But they pose several threats to the environments in which they live. The predation on earthworms by hammerhead worms is a significant concern, as earthworms play a vital role in maintaining healthy ecosystems. Earthworms contribute to soil aeration, nutrient cycling, and decomposition of organic matter. The decline in earthworm populations due to hammerhead worm predation can have cascading effects on soil health and plant growth. They prey on earthworms, which are essential to the health of compost, gardens, crops, and forests.
Toxicity and Handling Precautions
Some species of hammerhead worms produce tetrodotoxins, a potent neurotoxin also found in pufferfish. These toxins are used to overcome prey or protect eggs and themselves from predators. While encountering or accidentally making skin-to-worm contact won’t automatically kill you, being aware of what these flatworms are and exercising caution around them is recommended. People should avoid handling or holding hammerhead worms. If you touch any, wash your hands afterwards.
Read also: What Scalloped Hammerheads Eat
Hammerhead worms are also potential hosts for rat lungworms, as are snails and slugs. Humans can acquire this parasite by consuming undercooked or raw snails, slugs, freshwater shrimp, crabs, and frogs.
Safe Handling Practices
When handling flatworms, especially invasive hammerhead worms, it is crucial to take precautions. Use a stick, gloves, or paper towel to grab the worm and place it in a resealable plastic bag. If you accidentally touch it, ensure you wash and disinfect your hands immediately.
Reproduction
Flatworms are hermaphroditic, meaning they have both male and female reproductive organs used for sexual reproduction.
However, they more commonly reproduce asexually when a portion of their body pinches off and regrows another entire flatworm. So, don’t chop them with a hoe because each resulting piece could regenerate a new worm.
Asexual Reproduction
Asexual fragmentation is its main reproductive strategy in temperate regions and most individuals never develop sexual organs. Part of their body does naturally “fall off” and turn into a new individual, so don’t help them with that process. A small rear portion of the worm pinches off and develops a head within 10 days. This process occurs a few times a month.
Read also: A Defining Moment in the Reformation
Management and Control
There isn’t a true management tactic for these. No sprays or baits can be applied to prevent or control them. If you find a hammerhead worm and you choose to kill it, there are several options.
Prevention
There isn’t a true management tactic for these. No sprays or baits can be applied to prevent or control them.
Eradication Methods
First, don’t try to physically destroy or cut up the worms. Segmenting them can result in reproduction.
Salting them, like you would a snail or slug, will destroy them. Do be cautious about not getting salt in the soil around your plants. Spritzing the hammerhead worm with vinegar or citrus oil can also kill it. Other remedies, such as salt, vinegar solution, or citrus oil also are effective.
Apply salt or vinegar directly on the worm while it’s in the bag. Then, seal the bag and place it in the freezer for 48 hours. It should dissolve. Toss the sealed bag in the trash.
Hammerhead Worms in the Ecosystem
The concern that many have with hammerhead worms is that they feed on earthworms. However, most earthworms in Georgia are introduced species as well. Because hammerhead worms feed on the invasive earthworms such as jumping worms, some believe they should be left alone.
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