Eastern oyster drill (Urosalpinx cinerea)

Physical description

The Eastern oyster drill is a marine snail with a ribbed, textured shell. The shell can be yellow, yellow with brown streaks, gray, white, or orange on younger individuals. In a few Atlantic populations, drills can reach about 60mm in length (2.4 inches); in Washington, they are generally closer to 25mm (1 inch) and have been seen as large as 36mm (1.4 inches). The inside of the shell is purple, reddish brown, or yellow. The Eastern oyster drill possesses a dextrally (right-handed) coiled shell with a pointed spire, an open siphonal canal, and usually five whorls of the shell with between nine and 16 axial ridges on each whorl.

This species can be distinguished from the Japanese oyster drill by its open siphonal canal, shell design featuring axial ribs or vertical bump instead of ornate "spokes," absence of a pronounced "shelf-like" lip extending from its aperture (opening), and generally smaller adult size. The egg casings of both invasive oyster drill species have similarities and may be confused. In Washington, drills have been observed laying eggs anywhere from late February to September. The eggs are yellow, rubbery capsules slightly larger than a grain of rice; drills adhere the eggs to hard surfaces like rocks or oyster shells. Though similar in color and size, key features can help tell them apart. Japanese oyster drill eggs have frilled wings or folded edges like a taco, whereas Eastern oyster drill eggs are flattened and wider at the margins and much less cylindrical without folding edges.

The Eastern oyster drill can also be confused with native snail species, such as the dog whelk (Nucella lamellosa) and the dire whelk (Lirabuccinum dirum). Dog whelks primarily eat barnacles. Dire whelks primarily feed on limpets and snails, and sometimes scavenge on fish carcasses. Neither are considered pests of aquaculture or native ecosystems.

Dog whelks have a heavier, chunkier shell and are generally larger (commonly up to 54mm or 2.1 inches, but reportedly reaching 100mm or almost 4 inches). Their shells come in variations of smooth, smooth-banded, and ornamented by frills. Their egg casings can bear some resemblance to invasive drills, though the dog whelk eggs are cylindrical and vase shaped. They have radial symmetry, are not flattened like the Eastern oyster drill, and do not have folded edges like the Japanese oyster drill. The Oregon Institute of Marine Biology provides a good description of dog whelk in this PDF (PDF).

The invasive Eastern oyster drill has axial ridges or vertical bumps along the shell exterior that continue all the way around the shell into adulthood. In the native dire whelk, these axial ridges or bumps lessen as it grows into adulthood and become obscured and smoothed near the opening or aperture. Size can also help distinguish between the two. The dire whelk commonly grows to 50mm or 2 inches, whereas it is uncommon for the Eastern oyster drill to grow above 35mm in Washington.

Ecology and life history

Eastern oyster drills are found in the intertidal zone and have been recorded at depths reaching 120 feet. They prefer hard substrate, especially structure provided by Pacific oyster shells, clusters, and reefs/shellfish beds, where they feed, shelter, and lay their eggs). However, they can be found on or around human-created structures like cinderblocks, aquaculture gear, and debris. They can also be found (often in lower densities) in soft substrates.

Drills use acid secretion and a raspy tongue-like structure called a radula to puncture or "drill" holes through their prey's shell, secreting a digestive enzyme into their prey’s body to enable them to feed. Drills feed on a range of shellfish, such as Eastern oysters (Crassostrea virginica), Pacific oysters (Magallana gigas), Olympia oysters (Ostrea lurida), mussels (Mytilus spp.), and barnacles. They are especially fond of small juvenile or "spat" oysters. Larger shellfish, with thicker shells, are less vulnerable to drill predation. 

In the spring, drills lay benthic egg capsules the size of grains of rice on hard structures. Egg capsules are laid in clusters and are translucent, sometimes with a yellow or orange tint. They can be discerned from native whelk egg capsules by their pronounced flattened vase-like shape. Hatching juveniles are miniature versions of adults and emerge as "crawl aways" with no pelagic larval stage, limiting their dispersal ability. Because of this strategy, human-aided dispersal (such as moving shellfish, equipment, or debris with hitchhiking drills) is the chief risk of further spread in Washington. 

Geographic range

The species is native to the North American East Coast and was accidentally introduced to Willapa Bay sometime between the late 1800s and early 1900s, likely as hitchhikers with Eastern oysters (Crassostrea virginica); their known Washington distribution includes Willapa Bay and recent detections at Brinnon Tidelands in Hood Canal. This species has not spread as widely as the Japanese oyster drill and other invaders.

Eastern oyster drills were first introduced to San Francisco Bay, Calif., and later to Willapa Bay and Boundary Bay, BC. They are also found in several other California bays, generally (but not entirely) coincident with oyster culture. It is also thought that their East Coast range has expanded through accidental introductions. Isolated populations have also turned up in England and the Netherlands. 

The University of Washington's Ruesink Lab has more information on Eastern (and Japanese) oyster drills, including their distribution in Willapa Bay, where they are found in warmer and lower-salinity areas than Japanese oyster drills. Their distribution in Washington is not widespread, as the species has limited natural dispersal ability; WDFW is working to keep them from being introduced to new areas of shoreline.