Invasion History

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

General Invasion History:

Limulus polyphemus occurs on the Atlantic Coast of North America from Taunton Bay, Maine to the Yucatan Peninsula, Mexico (Gosner 1978). Occasional introductions are known in European waters, and on the coasts of California and New Zealand (Wolff 1977; Cohen and Carlton 1995; Ahyong and Wilkens 2011). Horseshoe crabs are often kept in private and public aquaria, and may sometimes be 'adopted' by fishermen or sailors and released in their home waters (Wolff 1977). Early occurrences in or near San Francisco Bay were probably introductions with transplanted Eastern Oysters (Crassostrea virginica) (MacGinitie 1949, cited by Wolff 1977). The benthic larvae occasionally occur in near-bottom plankton, although Wolff (1977) considered ballast water transport to be improbable. The introductions in San Francisco Bay and the northeast Atlantic have not resulted in established populations, possibly because water temperatures are not suitable for spawning (Wolff 1977).

North American Invasion History:

Invasion History on the West Coast:

A single specimen of Limulus polyphemus was caught off the Farallon Islands, west of San Francisco Bay, in 1886, and another in the Bay, in 1917 (Wolff 1977; Cohen and Carlton 1995). MacGinitie (1949, cited by Wolff 1977) reported that many young Atlantic Horseshoe Crabs were introduced to San Francisco Bay with oyster transplants, but did not mature or reproduce. Two more specimens were caught in San Francisco Bay in 1995 (Cohen and Carlton 1995). Additional releases of 'pets' by tourists and aquarists are possible.

Invasion History Elsewhere in the World:

In 1866, a large shipment of Limulus polyphemus was sent to Europe for the aquarium trade. Large numbers of unsold animals were released into the North Sea (Wolff 1977; Jensen and Knudsen 2005). From 1967, to 1977, more than 20 Atlantic Horseshoe Crabs were caught in European waters, from the North Sea (Germany) to the east coast of Denmark. Many of these crabs may have been released by the crews of Eastern European fishing fleets returning to the Baltic (Wolff 1977; Jensen and Knudsen 2005). We have no reports of later releases, although it is likely that some have occurred. One specimen was collected in New Zealand, on Great Barrier Island, NE of Auckland, in 1948. This may have been an aquarium release (Powell 1949, cited by Wolff 1977).


Horseshoe crabs (Class Merostomata) are not true crabs, and are more closely related to arachnids (spiders, scorpions, ticks, and mites). They lack antennae – instead, the first pair of feeding appendages are narrow feeding structures called chelicerae. Posterior to these are five pairs of walking legs. The body is partitioned into a shield-shaped anterior carapace, a posterior abdomen, and a long, thin, spike-like telson. The coxa (basal segment) of each walking leg is heavily armed with spines, called gnathobases, which tear up food and move it forward to the mouth. The first four pairs of walking legs are chelate (ending in paired claws) – the last pair has single claws, and has four leaf-like structures (used for digging) attached to the base of the claws. The underside of the abdomen bears five pairs of book gills, used for respiration and swimming. Adult females of Limulus polyphemus reach 600 mm total length – males are smaller. Newly hatched young, known as 'trilobite" larvae are about 1 cm long, and swim and burrow in the sediment (Barnes 1983).

Four species of horseshoe crabs occur worldwide. Limulus polyphemus is found on the Atlantic and Gulf coast of North America – the other three occur in East Asia (Gosner 1978; Barnes 1983).


Taxonomic Tree

Kingdom:   Animalia
Phylum:   Arthropoda
Subphylum:   Chelicerata
Class:   Merostomata
Order:   Xiphosura
Suborder:   Limulina
Family:   Limulidae
Genus:   Limulus
Species:   polyphemus


Potentially Misidentified Species



Limulus polyphemus (Atlantic Horseshoe Crabs) have separate sexes. They migrate into the shallow waters of bays, sounds, and estuaries. Mating and egg laying occurs on high tides at new and full moons in spring and summer. The smaller male climbs onto the back of the female, holding on with hooklike first legs, while the female partially buries herself in the sand. She lays 2,000 to 30,000 fertilized eggs in the sand of the intertidal zone. The eggs are 2-3 mm in size and covered by a thick membrane. The eggs hatch in about a month, on the next spring tide, into 'trilobite' larvae, with an overall horseshoe-crab shape, but with a short tail-spine, and only two pairs of book gills. The larvae actively swim and burrow in the sand and mud. Juveniles are common on shallow mudflats. They take 9 to 12 years to mature and may live for 19 years (Barnes 1983; Lippson and Lippson 1997).


bivalves, polychaetes, nermerteans


fishes, birds, humans (bait fishery)

Trophic Status:




General HabitatUnstructured BottomNone
General HabitatSalt-brackish marshNone
General HabitatOyster ReefNone
Salinity RangeMesohaline5-18 PSU
Salinity RangePolyhaline18-30 PSU
Salinity RangeEuhaline30-40 PSU
Tidal RangeSubtidalNone
Tidal RangeLow IntertidalNone
Vertical HabitatEpibenthicNone

Life History

Tolerances and Life History Parameters

Minimum Temperature (ºC)0None
Maximum Temperature (ºC)30None
Minimum Salinity (‰)10Smithsonian Marine Station 2002
Maximum Salinity (‰)40Smithsonian Marine Station 2002
Broad Temperature RangeNoneCold temperate-Warm temperate
Broad Salinity RangeNoneMesohaline-Euhaline

General Impacts

Introductions of Limulus polyphemus have failed to establish populations, and therefore have not had any economic or ecological impacts.

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
CAR-I Northern Yucatan, Gulf of Mexico, Florida Straits, to Middle Eastern Florida 0 Native Estab
NEA-II None 1866 Def Failed
NA-ET3 Cape Cod to Cape Hatteras 0 Native Estab
CAR-VII Cape Hatteras to Mid-East Florida 0 Native Estab
B-II None 1967 Def Failed
NEP-V Northern California to Mid Channel Islands 1886 Def Failed
P090 San Francisco Bay 1917 Def Failed
NA-ET2 Bay of Fundy to Cape Cod 0 Native Estab
B-I None 1971 Def Failed
B-III None 1976 Def Failed
NZ-IV None 1940 Def Failed

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude


Ahyong, Shane T.; Wilkens, Serena L. (2011) In the wrong place- Alien marine crustaceans: Distribution, biology, impacts, Springer, Dordrecht, Netherlands. Pp. 451-485

Barnes, Robert D. (1983) Invertebrate Zoology, Saunders, Philadelphia. Pp. 883

Cohen, Andrew N.; Carlton, James T. (1995) Nonindigenous aquatic species in a United States estuary: a case study of the biological invasions of the San Francisco Bay and Delta, U.S. Fish and Wildlife Service and National Sea Grant College Program (Connecticut Sea Grant), Washington DC, Silver Spring MD.. Pp. <missing location>

Gosner, Kenneth L. (1978) A field guide to the Atlantic seashore., In: (Eds.) . , Boston. Pp. <missing location>

Jensen, Kathe R.; Knudsen, Jorgen (2005) A summary of alien marine benthic invertebrates in Danish waters., Oceanological and Hydrobiological Studies 34 (suppl. 1): 137-161

Lippson, Alice Jane; Lippson, Robert L. (1997) <missing title>, Johns Hopkins University Press, Baltimore. Pp. <missing location>

MacGinitie, G. E.; MacGinitie, Nettie (1968) <missing title>, McGraw-Hill, New York NY. Pp. <missing location>

Smithsonian Marine Station at Fort Pierce 2007-2022 Indian River Species Inventory.

Wolff, Torben (1977) The horseshoe crab (Limulus polyphemus) in European waters,, Videnskabelige meddelelser fra Dansk naturhistorisk forening. 140: 39-42

Wolff, W. J. (2005) Non-indigenous marine and estuarine species in the Netherlands., Zoologische Verhandelingen 79(1): 1-116