Hammerhead Flatworm

This is a shovel-headed garden worm, wandering hammerhead worm, or hammerhead flatworm, Bipalium vagum — technically not a worm like an earthworm, but a land planarian. Planaria actually eat earthworms and other invertebrates. Planaria are way too cool and fascinating for me to get fully into here — check out this site (among others) for more information!

Bipalium vagum is a relatively small member of Bipalium. The hammer-shaped head can be black to dark brown, often with two darker patches separated by a lighter base color. The neck has a black collar going almost entirely around the flatworm’s body (broken only at the center ventrum). The body itself is light brown, with one central dorsal black stripe with a dark brown stripe on either side of it. This little guy (hermaphrodite, really) was about 25mm long.

Planaria actually reproduce primarily via asexual fragmentation, where larger individuals shed sections of themselves at the tail end, and the sections “regenerate” a new head and become full individuals. (If you cut a planarian in half, each piece will regenerate a new adult worm!)

Planarians move by using a long strip of strong, closely spaced cilia on their underside, called the creeping sole. The area secretes a thin film of mucus along which the cilia glide. If they fall off of something, they can sometimes lower themselves to the ground with a string of mucus. Here’s a terrible iPhone video of a Bipalium vagum moving:

Identified via iNaturalist.

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