Invasion History

First Non-native North American Tidal Record: 1955
First Non-native West Coast Tidal Record:
First Non-native East/Gulf Coast Tidal Record: 1955

General Invasion History:

The native range of Stramonita canaliculata is somewhat uncertain, because of confusion with S. floridana (Florida Rock Shell). Both species were formerly treated as subspecies of S. haemastoma and often simply recorded as the latter species. Stramonita canaliculata was believed to be confined to the Gulf of Mexico, while S. floridana occurred on the Atlantic coast from Florida to North Carolina (Sieling 1960; Abbott 1974). However, S. canaliculata has been reported from Georgia (Walker 1982; Hoese 1969, cited by Butler 1985). Claremont et al. (2011), found considerable geographical overlap between the two species, with S. canaliculata occurring on the Florida Atlantic coast at least as far north as the Indian River Lagoon and S. floridana occurring at locations in the Gulf to the Texas-Mexico border, and on the Yucatan Peninsula, although S. canaliculata was more common in the Gulf. They suggest that the two species may be differentiated more by ecological preferences, with S. floridana preferring more open, oceanic environments and S. canaliculata favoring more continental, estuarine shorelines (Claremont et al. 2011).

The northern limit of the Western Atlantic range of 'S. haemastoma' was believed to be Oregon Inlet, North Carolina, just north of Cape Hatteras, but in 1955-1956, living animals and recent shells were found in Chincoteague, Hog Island, and the lowermost Chesapeake Bay (Sieling 1960; US National Museum collections). Stramonita populations in these bays had been identified as S. floridana (Sieling 1960; Counts and Bashore 1991; Harding and Harasewych 2007), but Claremont et al. (2011) has re-identified them as S. canaliculata. These northern populations are considered to be probable introductions (Sieling 1960; Counts and Bashore 1991; Prezant et al. 2002), although natural dispersal of larvae from southern waters cannot be excluded. The source of these introductions could be either the Gulf of Mexico or S. canaliculata populations on the Atlantic coast.

North American Invasion History:

Invasion History on the East Coast:

In 1955, living specimens of Stramonita were found in Hog Island and Chincoteague Bays, Virginia (VA), extending the northward range of the genus by 240 km. Sieling (1960) considered the morphology of the shells to match shells from Louisiana, presumably S. canaliculata. Old shells, perhaps 80-100 years old were found in excavations of the now-closed Green Run Inlet, suggesting an early introduction, probably before 1883, when the inlet became unnavigable (Sieling 1960). However, this species was not found in a thorough 1913 survey of Assateague Island mollusks (Henderson and Bartsch 1914; cited by Sieling 1960). Sieling (1960) suggested that cold winters in the late 1800's and early 1900's may have reduced or eliminated early populations. In that case, the specimens found in the 1950's may have resulted from oyster transplants. In a 1988-1989 survey, S. haemastoma was rare 'with the decline of oyster populations' (Counts and Bashore 1991), but they were found again in 1994-1996 survey (Prezant et al. 2002).

Stramonita has not been reported from Chesapeake Bay proper, until recently (Andrews 1956; Wass 1972), but U.S. Natural History Museum collections include one worn specimen found at Virginia Beach in 1955. In 2005, four specimens were collected from Deep Creek, Newport News, VA on the James River, and in 2006 13 specimens were collected from Back River, a York tributary near Williamsburg, VA (Harding and Harsewych 2007). Harding and Harsewych (2007) used morphological and genetic evidence to identify snails as S. floridana, but Claremont et al. (2011) re-analyzed their data, and identified the Chesapeake and Atlantic bay specimens, and their Indian River Lagoon reference specimens, as S. canaliculata.

Although larvae of the S. haemastoma complex are capable of long-distance transport, and adults have been found on logs far at sea, natural dispersal northward is unlikely because the prevailing currents near Cape Hatteras run southward, while the Gulf Stream further offshore moves eastward (Bumpus and Lauzier 1965). Therefore, coastal shipping or oyster transplants seem the likeliest source of the populations in the eastern bays.

Invasion History Elsewhere in the World:

In 1974-1976, snails identified as S. haemastoma floridana were found in Miraflores Locks on the Pacific side of the Panama Canal, together with the native Pacific form, S. biserialis (U.S. Museum of Natural History collections). We are unsure of the status of these specimens and genetic studies would be needed to determine their origin.


The shell of Stramonita canaliculata is solid and dextrally coiled, with a prominent pointed spire. Mature shells have 5-7 whorls, with a double row of nodules on the shoulder of the whorls. The sculpture is highly variable, but includes spiral grooves with transverse ribs, which can vary from faint to prominent. The suture between the whorls is usually very prominent in this species. The aperture is oval, with a short siphonal canal. The inner surface of the lip is finely crenulated. This shell can reach 117 mm, but 70-80 mm is a more typical adult size. The shell is gray with brown markings, while the aperture is pink. Description from: Sieling 1960, Abbott 1974, Morris 1975, Butler 1985, Harding and Harasewych 2007, and Claremont et al. 2011.

Stramonita (formerly Thais) haemastoma (Linnaeus 1767), described from Europe, was formerly treated as a widespread species, containing many subspecies in warm-temperate and tropical regions on both sides of the Atlantic and in the tropical Eastern Pacific. These subspecies have now been raised to the status of full species, on the basis of morphology and genetics (Liu et al. 1991; Vermeij 2001; Claremont et al. 2011). Two species are found on the southeast coast of North America. Claremont et al. (2011) show mapped records of S. canaliculata from central Florida, through the Gulf coast to the Yucatan, and records of S. floridana from Georgia to Texas. The two species overlap, but S. canaliculata is more common on the Gulf coast (Abbott 1974; Liu et al. 1991; Claremont et al. 2011). However, morphology of both species is highly variable, so molecular techniques are useful for identification (Liu et al. 1991; Harding and Harasewych 2007; Claremont et al. 2011). Harding and Harasewych (2007) identified specimens of Stramonita from Chesapeake Bay and Atlantic bays of Virginia as S. floridana, based on morphology and DNA barcoding. However, Claremont et al. (2011), in a wider review of the genus, re-interpreted Harding and Harasewych's molecular data and identified the Virginia specimens as S. canaliculata. We have tentatively accepted this identification, but further sampling and molecular studies are needed to determine the identity of Stramonita in the Chesapeake and Atlantic coastal bays.


Taxonomic Tree

Kingdom:   Animalia
Phylum:   Mollusca
Class:   Gastropoda
Subclass:   Prosobranchia
Order:   Neogastropoda
Family:   Muricidae
Genus:   Stramonita
Species:   canaliculata


Fusus canaliculatus (Gray, 1839)
Thais canaliculata (None, None)
Thais haysae (Clench, 1927)
Thais floridana haysae (None, None)
Thais haemastoma canaliculata (None, None)
Thais haemastoma haysae (None, None)
Stramonita haemastoma canaliculata (None, None)

Potentially Misidentified Species

Stramonita floridana
A very similar, partly sympatric species, ranging from North Carolina to Yucatan, formerly considered conspecific. Morphology of S. floridana and S. canaliculata is highly variable and molecular methods are helpful in their identification (Claremont et al. 2011).

Stramonita haemastoma
East Atlantic form, ranges from Spain to Namibia. Was formerly considered the type subpecies, out of many (Claremont et al. 2011).



Stramonita canaliculata is a large, predatory marine gastropod. Sexes are separate and the snails usually reach maturity in 8-10 months, at 50-60 mm shell length. In protected environments with abundant food, snails 2-3 months old have been seen depositing eggs (Butler 1985). Fertilization is internal. In the Gulf of Mexico, eggs are laid in April through August, in bunches of up to 150 capsules, each containing 500-6,000 eggs. The number of capsules, size of the capsules (4-18 mm), and number of eggs per capsule increase with the age and size of females. A long-lived female could potentially produce 10 million eggs in her lifetime (Butler 1985). The eggs usually hatch in about 14 days, but can hatch in as early as 10 or as late as 39 days (Butler 1985) varying with temperature (Butler 1985). The eggs hatch into planktotrophic veligers, which at 25°C take 28 days to develop at high food levels, but can take up to 172 days at very low food levels. The larvae metamorphose at ~1.0-1.5 mm shell length (Doberteen and Pechenik 1987).

Stramonita canaliculata inhabits rocky shores and oyster beds in shallow water, but sometimes as deep as 11 m (Butler 1985; Rosenberg 2014). The snails apparently survive temperatures as low as 5°C in Chincoteague Bay (Harding and Harasewych 2007). In experiments, S. canaliculata survived for 28 days at 35°C with ~50% mortality (Brown and Stickle 2002). Snails acclimated to 20 PSU survived at 10 PSU without mortality, and some on a Florida Reef survived a gradual decrease to 5 PSU. However, this species prefers the more saline parts of estuaries (Butler 1985). Spawning usually occurs at 21-28°C and at salinities above 20 PSU (Butler 1985). Feeding rates were reduced during air exposure, when the conditions of an intertidal oyster reef were simulated (Brown and Stickle 2002).

Stramonita canaliculata is a carnivorous snail, feeding on barnacles, mussels, and small (<30 mm) and large Eastern Oysters (Crassostrea virginica), in that order of preference. Other reported prey are Donax variabilis (Coquina), Rangia cuneata (Gulf Wedge Clam), Mercenaria mercenaria (Hard Clam), and Crepidula plana (Eastern White Slippersnail) (Butler 1985). The snail rasps a hole in the shell with its radula and secretes enzymes to digest the prey. They scavenge on dead oysters and starved snails will cannibalize others of their own species. Feeding stops at temperatures below 12°C and salinities below 7.5 PSU (Butler 1985). Adults of this snail have few predators, because of their thick shells. They are parasitized by trematodes, and attacked by the boring sponge Cliona truitti (Butler 1985).


barnacles; mussels; clams; oysters

Trophic Status:




General HabitatUnstructured BottomNone
General HabitatOyster ReefNone
General HabitatMarinas & DocksNone
General HabitatRockyNone
Salinity RangeMesohaline5-18 PSU
Salinity RangePolyhaline18-30 PSU
Salinity RangeEuhaline30-40 PSU
Tidal RangeSubtidalNone
Tidal RangeLow IntertidalNone
Vertical HabitatEpibenthicNone

Tolerances and Life History Parameters

Minimum Temperature (ºC)5.2Mean January temperature, 2001-2004, at a Chincoteague Bay buoy (Harding and Harasewych 2007)
Maximum Temperature (ºC)35Experimental. Brown and Stickle 2002
Minimum Salinity (‰)5Field, on a Florida reef (Higgins 1938, cited by Butler 1985). Snails acclimated to 20 PSU survived transfer to 10 PSU, without mortality(Butler 1985)
Maximum Salinity (‰)36Typical Gulf of Mexico and Atlantic salinity, but S. canaliculata probably tolerates higher salinities in some Gulf lagoons.
Minimum Reproductive Temperature21Butler 1985
Maximum Reproductive Temperature28Butler 1985
Minimum Reproductive Salinity20Butler 1985
Maximum Reproductive Salinity35Typical Gulf of Mexico and Atlantic salinity, but S. canaliculata probably tolerates higher salinities in some Gulf lagoons.
Minimum Length (mm)16.5Butler 1985
Maximum Length (mm)112Rosenberg 2014
Broad Temperature RangeNoneWarm temperate-Tropical
Broad Salinity RangeNoneMesohaline-Euhaline

General Impacts

Stramonita canaliculata together with S. floridana, are regarded as the most serious oyster predators in more saline estuaries in many parts of the southeastern United States. 'There is consensus that the southern oyster drill prevents profitable oyster culture on thousands of hectares of otherwise suitable grounds along the Gulf coast, but methods for controlling this predator are essentially absent' (Butler 1985). In Chincoteague and Hog Island Bays, it represented a threat to Crassostrea virginica (Eastern Oyster) populations when it was first discovered (Sieling 1960), but the decline of oysters due to disease and other factors seems to have limited S. canliculata's population growth (Counts and Bashore 1991). Oyster populations in Atlantic Bays have recovered to some extent (Fofonoff, personal observations), and S. canaliculata has persisted and appeared in lower Chesapeake Bay (Prezant et al. 2002). If this snail becomes abundant it could affect the recovery of oyster populations (Harding and Harasewych 2007).

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
CAR-VII Cape Hatteras to Mid-East Florida 0 Native Estab
CAR-I Northern Yucatan, Gulf of Mexico, Florida Straits, to Middle Eastern Florida 1837 Native Estab
CAR-II None 0 Native Estab
NA-ET3 Cape Cod to Cape Hatteras 1955 Def Estab
M130 Chesapeake Bay 2005 Def Unk
M120 Chincoteague Bay 1955 Def Estab
M128 _CDA_M128 (Eastern Lower Delmarva) 1955 Def Estab
S190 Indian River 0 Native Estab
S183 _CDA_S183 (Daytona-St. Augustine) 0 Native Estab
S130 Ossabaw Sound 0 Native Estab
S206 _CDA_S206 (Vero Beach) 0 Native Estab
G080 Suwannee River 0 Native Estab
G110 St. Andrew Bay 0 Native Estab
G130 Pensacola Bay 0 Native Estab
G190 Mississippi River 0 Native Estab
G160 East Mississippi Sound 0 Native Estab
G310 Corpus Christi Bay 0 Native Estab

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude


Abbott, R. Tucker (1974) American Seashells, Van Nostrand Reinhold, New York. Pp. <missing location>

Brown, Kenneth M.; Stickle, William B. (2002) Physical constraints on the foraging ecology of a predatory snail, Marine and Freshwater Behavior and Physiology 35(3): 157-166

Bumpus, Dean F., Lauzier, Louis M. (1965) Surface circulation on the continental shelf off eastern North America between Newfoundland and Florida., Serial Atlas of the Marine Environment <missing volume>: <missing location>

Butler, Philip A. (1985) Synoptic review of the literature on the southern oyster drill Thais haemastoma floridana, NOAA Technical Report NMFS 35: 1-9

Byron, Kevin W.; Smee, Delbert L. (2012) Effects of flow on the behavior of the Southern Oyster Drill Stramonita haemastoma in response to exudates from oysters and oyster reef fauna, Journal of Shellfish Research 31: 93-100

Claremont, Martine; Vermeij, Geerat J.; Williams, Suzanne T.; Reid, David G. (2013) Global phylogeny and new classification of the Rapaninae (Gastropoda: Muricidae), dominant molluscan predators on tropical rocky seashores, Molecular Phylogenetics and Evolution 66: 91-102

Claremont, Martine; Williams, Suzanne T.; Barraclough, Timothy G.; Reid, David G. (2011) The geographic scale of speciation in a marine snail with high dispersal potential, Journal of Biogeography 38: 1016-1032

Counts, Clement L. III; Bashore, Terry L. (1991) Mollusca of Assateague Island, Maryland and Virginia: A reexamination after seventy-five years., Veliger 34(2): 214-221

Dall, William Healey (1889) A preliminary catalogue of the shell-bearing marine mollusks and brachiopods of the south-eastern coast of the United States, Bulletin of the United States National Museum 37: 1-221

Doberteen, Ross A.; Pechenik, Jan A. (1987) Comparison of larval bioenergetics of two marine gastropods with widely differing lengths of larval life, Thais haemastoma caniculata (Gray) and Crepidula fornicata (L.), Journal of Experimental Marine Biology and Ecology 109: 173-191

Florida Museum of Natural History 2009-2013 Invertebrate Zoology Master Database. <missing URL>

Harding, Juliana M.; Harasewych, M. G. (2007) Two modern records for the southenr oyster drill Stramonita haemastoma floridana (Conrad, 1837( in Chesapeake Bay, USA., Nautilus 121(3): 146-158.

Harvard Museum of Comparative Zoology 2008-2021 Museum of Comparative Zoology Collections database- Malacology Collection. <missing URL>

Liu, L. L.; Foltz, D.W.; Stickle, W.B. (1991) Genetic population structure of the southern oyster drill Stramonita (=Thais) haemastoma., Marine Biology 111: 71-79

Morris, Percy A. (1975) A field guide to shells of the Atlantic, Houghton-Mifflin, Boston. Pp. <missing location>

Prezant, Robert; Counts, Clement L.; Chapman, Eric J. (2002) Mollusca of Assateague Island, Maryland and Virginia: additions to the fauna, range extensions, and gigantism., Veliger 45: 337-355

Roller, Richard A.; Stickle, William B. (1989) Temperature and salinity effects on the intracapsular development, metabolic rates, and survival to hatching of Thais haemastoma caniculata (Gray) (Prosbranchia: Muricidae) under laboratory conditions, Journal of Experimental Marine Biology and Ecology 125: 235-251

Rosenberg, Gary 1995-2023 Malacolog 4.1.

Sieling, Fred W. (1960) A notable range extension of the southern drill, Thais haemastoma floridana, into Chincoteague Bay, Chesapeake Science 1: 212-215

Stickle, William B.; Kapper, Martin A.; Liu, Li-Lian; Gnaiger, Erich; Wang, Shiao A. (1989) Metabolic adaptations of several species of crustaceans and molluscs to hypoxia: tolerance and microcalorimetric studies, Biological Bulletin 177: 303-312

U.S. National Museum of Natural History 2002-2021 Invertebrate Zoology Collections Database.

Vermeij, Geerat J. (2001) Distribution, history, and taxonomy of the Thais clade (Gastropoda: Muricidae) in the Neogene of tropical America., Journal of Paleontology 25(3): 697-705

Walker, Randal L. (1982) The gastropod Thais haemastoma in Georgia: T. h. floridana or T. h. canaliculata?, Gulf Research Reports 7(2): 183-184

Wells, Harry W. (1961) The fauna of oyster beds, with special reference to the salinity factor, Ecological Monographs 31: 239-266