Photo: Jill Spohn
There have been 41 observations on iNaturalist of Hammerhead Worms (subfamily bipalinae) in Fairfax County. There are more than one species, all nonnative and feeding on earthworms. One recent sighting was a thin, foot-long worm with the distinctive hammer head.
Cutting them or smashing them may result in regeneration. They also emit a toxin, so grabbing them barehanded or getting parts on you may result in toxic burns. If necessary, they can be destroyed by bagging and freezing.
Here is a link to a NC State extension article that includes great info about Wandering Broadhead Planarians: Terrestrial Flatworms, Land Planarians & Hammerhead Worms | NC State Extension Publications (ncsu.edu)
Please take or send samples to our local Virginia Cooperative Extension office.