Chesapeake Bay Program - Oyster Drill

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	Mollusk Bivalve Gastropod

Background

Photo by: Eric Zabel
Courtesy the University of Rhode Island & Dr.Emily Carrington

Urosalpinx cinerea, the Atlantic oyster drill, is an oval mollusk that grows to about 1 3/4 inches in length and proliferates on and among rocks, wharf pilings and the rich three-dimensional habitat of oyster reefs along both the Atlantic and Pacific coasts. It is one of most voracious predators of the common eastern oyster. Along the East Coast its range extends from the Gulf of St. Lawrence to Florida.

The Atlantic oyster drill does not exclude any forms of shellfish from its diet. It often consumes other bivalves, gastropods and crabs.

This small snail has a knobby, oval shell that is usually gray, yellowish-white, or purplish in color, and it has a thin, sharp lip with deep, brown ribs along its convex whorls, criss-crossed by thin spiral ridges. It has about 9 to 12 rounded vertical folds per whorl and a short siphonal canal. The inside of its aperture is also purplish. A dark, hornlike "door" or operculum protects the snail when it retracts its head completely within its shell. The oyster drill can live from above the low-tide line to waters nearly 50 feet deep.

PHOTO: Courtesy of Virginia Institute of Marine Science - Juliana Harding

Photo by: Juliana Harding
CourtesyVirginia Institute of Marine Science

Urosalpinx cinerea uses a secreted chemical to soften the shell of its prey and deploy its radula, the long, toothed structure that extends from its mouth like a file and drills holes in tough oyster shells. It then inserts its proboscis into the hole and feeds on the soft meat of the oyster. Although it seems to prefer juvenile oysters, the snail also drills through the shells of mussels, barnacles and other tough-shelled aquatic animals that inhabit the reefs.

The prolific oyster drill spawns throughout the summer months, laying its eggs in round, capsule-like structures that are anchored by thin stems to pilings, rocks or reefs. Larvae crawl from these egg cases within 6 to 8 weeks.

The oyster drill is no favorite of Chesapeake Bay watermen; however, those who cultivate oysters try to grow them upriver, in lower salinity waters which the oyster can tolerate, but not the snail.

Other Sites of Interest:

Atlantic Oyster Drill - General background information on the Atlantic Oyster Drill.
Two Things You Can Do To Improve The Oyster Beds - Information on how to recognize Oyster Drills and their egg casings from New Hampshire Department of Environmental Services, Shellfish Program.
Field Guide to the Rocky Shores of Rhode Island - General information on the Atlantic Oyster Drill and other Atlantic coast organisms.

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For more information, contact the Chesapeake Bay Program Office:
410 Severn Avenue, Suite 109, Annapolis, MD 21403 / Tel: (800) YOUR-BAY / Fax: (410) 267-5777.