How bad are shovel headed worms when it comes to killing earthworms? I’ve found a few lately and dislike them—even the chickens are freaked out about them! I understand that they are some type of land flatworm in the Planaria family and are invasive. They look like some kind of alien as they scan their heads back and forth over the ground. This was the largest at almost 1 foot long. —Mike Hilbig, HobbyFarms.com reader
Based on the photo you submitted, Mike, you’ve identified this worm correctly. It’s one of the four or five invasive land planarian species now found in different corners of the United States. Many of these species were introduced into North America and Europe from Asia through the horticultural trade and arrived hidden in the soil of potted tropical plants. Over the last century or so, several of these land flatworm species have established breeding populations in the southeastern United States and California, and they’re spreading quite rapidly where conditions are favorable to their survival.
The planarian worm you’ve come in contact with is likely Bipalium kewense which is the most common land species found in the Southeast. This unusual creature has many common names, such as the hammerhead worm, shovel headed worm or arrowhead worm, due to its unique fan-shaped “head”—though this is more of an appendage than a head because it doesn’t contain the mouth (which is actually near the middle the body) or eyes (as land planarians actually don’t have true eyes).
Interestingly, while land planarians can reproduce by laying eggs, their primary mode of reproduction is through a process known as fragmentation or budding, where the worms detach a piece of their tail that will grow into a new worm.
As you suggest, these unusual-looking invasive worms can get quite large, with adult worms reaching nearly a foot in length when they stretch out during their crawling locomotion. Land planariums are covered with a layer of mucus on their lower half, allowing them to transverse a variety of rough surfaces and leaving a glistening slime trail similar to that of snails or slugs. These creatures are primarily active during the evening and night hours to avoid the daytime heat which can desiccate them.
Unlike your friendly night crawlers, land planarian species are predators and feed on a number of prey, including snails, various insect larva, slugs and earthworms. The species pictured (Bipalium kewense) does primarily feed on earthworms. Where large concentrations of these land planarians are found, there can be a noticeable decline in earthworm populations. That being said, many entomologists don’t believe that the presence of these long slimy worms necessarily signals the end of earthworms, as both species seem to be able to coexist in some form of balance.