It’s the time of the year when hammerhead flatworms start making their way into the news cycle again, so here’s another story to add to the pile.
Flatworms are predators that prey on soft-bodied creatures like earthworms, snails, slugs, and small arthropods. Flatworms wrap themselves around their prey and digest it on the underside of their body -- that’s where their mouth is.
The hammerhead flatworm has a half-moon-shaped head and is usually light/honey-colored with one to five dark dorsal stripes. They can grow up to 15 inches long and are very narrow.
Some flatworms, including the hammerhead flatworm, secrete chemicals through their skin to make themselves noxious to predators and help them digest their prey. Those chemicals can also irritate human skin.
If you touch one of these worms you should make sure to wash your hands. According to the Penn State Extention, there are no documented cases of pets or children being sickened by eating or handling flatworms.
The hammerhead flatworm has been known to reproduce by pinching off a piece of itself. After about 10 days, a head begins to form on the piece of worm that was left behind. That is why if you find a hammerhead flatworm you should dispose of the entire thing and not cut it up.
These worms prefer hot, humid environments. They do well in greenhouses, tropical and subtropical areas. It is known to spread from greenhouses and as a “hitchhiker” in the landscaping, mulch, and nursery industries.
According to the Texas Invasive Species Institute, hammerhead flatworms can potentially be found in greenhouses in Michigan.
- Natural habitats: AL, CA, FL, GA, LA, MS, NC, SC, TX. (Possible temporary populations: AZ, MA, NH)
- Greenhouses: AL, CA, GA, IL, KY, MA, MI, NC, NJ, NY, OH, OK, SC, TN
According to the North Carolina Extension, the concern that the worms pose an issue to native invertebrates may be true in areas where they are newly introduced -- but is likely not the case in places where they have been established for decades.
Hammerhead flatworms can be killed with citrus oil and salt. They can also be sprayed with a combination of citrus oil and vinegar or just vinegar alone. The vinegar must be applied directly to the flatworm. Placing them in a Ziploc bag with salt or vinegar is one method to ensure they do not try to escape.
There is some good news though. According to the Penn State Extention, terrestrial flatworms are known to feed exclusively (or nearly exclusively) on non-native earthworms (like invasive jumping worms) in urban and suburban areas.
Jumping worms look similar to earthworms but can easily be identified because of the way they thrash around. Jumping worms have been detected in Michigan and pose a threat to the ecosystem because of the amount of leaf litter they consume.
There are currently no proven methods to control or manage populations of jumping worms, so the state recommends placing them inside sealed plastic bags and freezing or heating them before sending them to a landfill.
You can learn more about this invasive worm from the Texas Invasive Species Institute, the Penn State Extention, and the North Carolina Extension.