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 (smaller individuals) and can reach about 60mm in length (2.4 inches); it is generally closer to 35mm (1.4 inches) in length. The inside of the shell is purple, reddish brown, or yellow. The Eastern oyster drill possesses a dextrally coiled shell with a pointed spire, an open siphonal canal, and usually 5 whorls of the shell. The shell features axial ribs on its spires.

The species can be distinguished from the Japanese oyster drill by its open siphonal canal, shell design featuring ribbing instead of ornate "spokes," absence of a pronounced "shelf-like" lip extending from its aperture (opening), and generally smaller adult size.

This species can be confused with native species of drilling predatory snails, such as the native dogwhelk (Nucella lamellosa) to which it (and its egg casings) bear some resemblance. Native dogwhelks primarily eat barnacles and are not considered pests of aquaculture or native ecosystems, contrasting with the preferred diet and status of the non-native Eastern oyster drill. Native 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). They come in smooth-shelled, smooth-banded, and frilly shelled variations. Their egg casings lack the twist and vase-shape of non-native drills, instead resembling a smooth, torpedo-like shape. A good description of native Nucella lamellosa can be found here, courtesy of the Oregon Institute of Marine Biology.

Ecology and life history

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

Drills use secretion of an acid and a raspy tongue-like structure called a radula to puncture or "drill" holes through their prey's shell, then using secretion of a digestive enzyme into the body of their prey 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. 

Drills lay benthic rice-grain-sized egg capsules on hard structures in Spring. Egg capsules are laid in clusters and are translucent, sometimes with a yellow or orange-ish tint. They can be discerned from native whelk egg capsules by their pronounced twisted vase-like shape. Hatching juveniles are miniature versions of adults and emerge as "crawl away" juveniles with no pelagic larval stage--which limits 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 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 only Willapa Bay as this species has not spread as widely as the Japanese oyster drill and other invaders. They were first introduced to San Francisco Bay, CA and later to Willapa Bay, and Boundary Bay, BC. Eastern oyster drills are also found in several other California bays, generally (but not entirely) coincident with oyster culture. It is also thought that their North American East coast range has been expanded through accidental introductions and 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. Its distribution in Washington is still localized to Willapa Bay as the species has limited natural dispersal ability, and WDFW is working to keep it from being introduced to new areas of our shoreline.