Water Caltrop
Exotic Aquatic Invasive Species

The Return of the Non-Native


Water Caltrop (Trapa bicornis),a.k.a. Water chestnut, Buffalo nut, Bat nut, Devil pod, Ling nut, Singhara, or Pani-phal, has returned to our watershed and is expanding.

At a workshop of interested agencies and organizations on November 15, 2019, we were dismayed to learn that the exotic aquatic genus we thought had been eliminated from our area has been spreading silently, infesting several ponds in our watershed. There seems to be no one at a Federal, state, or local level who can take charge of stopping the spread.

Ponds which have known infestations in our watershed are at Vienna Metro, Brookfield Pond, the Northern Virginia Community College pond, and a stormwater pond in Merrifield owned by Inova. Geese carrying the barbed seedpods on their feathers seem to be the primary vector.

Previous appearances of this species in Northern Virginia were misidentified as the closely-related Trapa natans, essentially the same weed with four points on the seed pods, rather than two. Trapa natans is well established in the northeast U.S.

Water caltrop forms thick floating mats that can expand exponentially, shading out native submerged aquatic vegetation, causing decines in disolved oxygen, and interfering with boating.

USPS map of Trapa bicornis locations Select "Records" tab for text details of locations.
USGS Trap bicornis description
2014 Eradicaation Effort


Sinister seed of Water Caltrop, a.k.a. Bat Nut