by Andrea Laine, EMGV

In September, a fellow master gardener found a strange-looking worm crawling across her porch. At 8 to 12 inches long it was hard to miss.

A few weeks later there was another one under a container in her ornamental garden. Since it looks a lot like an earthworm and earthworms are beneficial to a garden, she let it be. And then she learned it’s true nature. The worm, commonly referred to as a land planarian or hammerhead flatworm (Bipalium kewense and Dolichoplana striata are two species), is an invasive species from Southeast Asia and its favorite food source is the gardeners’ beloved earthworms.

Hammerhead flatworms thrive in high temperatures and humidity. They are typically found in dark, moist areas such as under rocks or logs, beneath shrubs, and in leaf litter or garden debris. They may appear on the soil surface after a heavy rain. The worms can endure freezing temperatures by hiding under objects or in commercial greenhouses where they arrive in container plants. Though this was my friend’s first sighting of one, they have been present in the U.S. for more than a century. Like Count Dracula, they shun daylight, feeding and moving about under the cover of darkness.

Unfortunately, the worms mucus membrane repels would-be predators. And don’t even think about squishing one – they can reproduce via fragmentation. But when food resources are low, the land planarian resorts to cannibalism. So, they may be their own worst enemy, afterall.

Resources and Further Reading:

From the Texas Invasive Species Institute: http://www.tsusinvasives.org/home/database/bipalium-kewense

From the University of Florida Entomology and Nematology Department: http://entnemdept.ufl.edu/creatures/misc/land_planarians.htm

A master gardener in Galveston, Texas chooses a more positive outlook on the land planarium: https://aggie-horticulture.tamu.edu/galveston/beneficials/beneficial-57(partial)_land_planarian.htm

Photo credit:
https://commons.wikimedia.org/wiki/File:Platydemus_manokwari_in_Florida_PeerJ2015_fig-1-full.pmg