Northeastern Beach Tiger Beetle Fact Sheet
Northeastern Beach Tiger Beetle
Cicindela dorsalis dorsalis
New York Status: Extirpated
Federal Status: Threatened
The northeastern beach tiger beetle has been described as a handsome, sand-colored insect. The white to light tan wing covers on the insect's back are often marked with fine dark lines. The head and thorax (chest area) are bronze-green. Overall length varies from 1/2 to 3/5 inch (13-15.5 mm). True to their name, they grasp prey with long, sickle-like mandibles (mouthparts) in an aggressive, "tiger-like" manner. Larvae are also predatory and similarly equipped.
Northeastern beach tiger beetles have a full, two-year life cycle. Adults emerge in late June, reach peak abundance by mid-July, and decline through early September. They feed, mate and bask at the water's edge on warm, sunny days. Some adults are also active on warm, calm evenings. High body heat is necessary for maximum predatory activity. Foraging occurs in the damp sand of the intertidal zone; prey species include lice, fleas, and flies. Adults also regularly scavenge dead crabs and fish.
Mating and egg-laying occur from late-June through August. Females deposit their eggs in the sand after mating, higher up the beach in the dunes. Eggs hatch and larvae appear in late July and August. Larvae experience three developmental stages or "instars." Most larvae reach the second instar by September and a few reach the third instar well into November, when larvae are still active.
Most overwinter as second instars. Next year, these same individuals overwinter again, this time as third instars. Overwintering occurs high up the beach; storms and wave activity are thus avoided. Both second and third instars emerge from winter inactivity in mid-March. Third instar larvae emerge, pupate in the bottom of their burrows, and re-emerge as winged adults in June, two full years after the eggs were laid.
Larvae live in vertical burrows located in the upper intertidal to high drift zone, where prey is most abundant. Larvae forage from their burrows, preying on passing insects. Their primary food sources are beach fleas, lice, flies and ants. Larvae are regularly covered during high tide; sand moisture is important. Larvae lack a hard shell and are subject to desiccation. They avoid hot, dry conditions. During the summer months they are inactive, going through a period of aestivation. With each successive stage of development, larvae grow in size and burrow deeper, going from 4 to 6-7 to 9-14 inches into the sand.
Populations of tiger beetles normally experience very high larval mortality and dramatic year-to-year, two to three fold fluctuations in abundance, sometimes resulting in local extinction. Weather factors such as flood tides, hurricanes, erosion and winter storms, mortality due to predators and parasites, and recreational beach use all contribute to the population declines. Natural enemies of adults include robber flies (Asilidae), birds and spiders. Larvae are preyed upon by parasitic, wingless wasps (Methocha), which lay their eggs on the tiger beetle larvae. The larval wasps develop by eating the larval tiger beetles.
Distribution and Habitat
Early records indicate that the northeastern beach tiger beetle occurred in "great swarms in July" along coastal beaches from Martha's Vineyard south to New Jersey and on both sides of Chesapeake Bay in Virginia and Maryland. It was very common on Rhode Island and Long Island beaches. Today, it is extirpated from the northern Atlantic Coast with the exception of a tiny population of fewer than 40 adults on Martha's Vineyard, Massachusetts. This is the only known population north of Maryland.
Over 50 sites occur in the Chesapeake Bay area; half of these have over 100 adults with 16 having over 500. Ideal habitat for the adult beetles and their larvae are wide, undisturbed, dynamic, fine sand beaches. The most important consideration, though, is limited use and disturbance by vehicles and humans.
The northeastern beach tiger beetle is currently extirpated from New York State. During the last 20 years, the beaches on Long Island have been subject to increasing vehicular traffic. Surf fishermen, commercial seiners, and beach recreationists in general use 4-wheel-drive trucks and other off-road vehicles on the beaches, especially in the intertidal zone. Foot traffic can be heavy. The impacts on larvae can be considerable, compacting burrows and crushing individuals. The fact that the tiger beetle is in the larval stage for two years increases the significance of these disturbances.
Although there are many populations in the Chesapeake Bay area, most are threatened by activity associated with human population increases. Developmental pressure, with concurrent beach alteration, beach stabilization structures, and recreational activities, have greatly altered the beetle's habitat along the Atlantic Coast. The continual disturbance or disruption of occupied habitats has eliminated many populations. A series of nearby or contiguous populations is probably necessary to naturally re-establish populations that have been locally depleted or extirpated. The decrease in habitat availability and a reduced number of populations make it difficult for beetles to recover from population declines. Long-term survival of this species is probably dependent upon its ability to disperse for considerable distances to colonize transient or well separated habitats, something which is perhaps unlikely without outside help. While mark-recapture study results have shown the beetles capable of traveling 5-12 miles from their original capture site, it might not be enough to reach the nearest suitable habitat.
The natural balance between the beetles and their primary predators has also been altered by habitat degradation and other factors. In some cases, these natural enemies may now pose a significant threat to the beetles.
The northeastern beach tiger beetle is listed as endangered by Maryland and Massachusetts. Threatened status has been proposed by Virginia.
Management and Research Needs
Detailed knowledge of certain aspects of distribution, annual and seasonal abundance, and ecology have only recently been gained, and much remains to be learned. Controlling access to beach areas and limiting foot traffic and off-road vehicle use are being considered and/or implemented at known locations of the northeastern beach tiger beetle. There are also a few remote islands in New England and New York (Gardiners Island) that need to be searched and checked or re-checked for the presence or absence of additional populations.
The objective of recovery efforts is to restore this threatened species to a secure status within its historical range. This could be accomplished by translocating beetles. Reestablishment methodology needs to be developed and survivorship maximized. Research is needed to determine whether the population on Martha's Vineyard is the same subspecies as those in the Chesapeake Bay area, the likely source of beetles for translocating. Most potential translocation sites are not currently suitable due to beach traffic, etc. This will need to be addressed prior to translocation. Also, existing sites in the Chesapeake Bay area need to be protected. Access must be controlled; barriers, like fencing, must be erected and areas patrolled. Habitat management will also be necessary. Phragmites control measures have been implemented in some instances. Further study is also needed to determine the effects of oil spills and other pollutants on beetle larvae. Another issue relates to beach nourishment (adding sand to a beach) programs, which could potentially destroy larvae directly, while benefiting the beetle in the long run.
Boyd, H. P. 1978. The tiger beetles (Coleoptera:Cicindelidae) of New Jersey, with special reference to their ecological relationships. Trans. Amer. Entomol. Soc. 104:191-242.
Luebke, J. I. and D. R. Beatty. 1987. Natural history and population decline of the coastal tiger beetle. Cicindela dorsalis dorsalis Say (Coleoptera:Cicindelidae). Virginia J. Sci. 38(4):293-303.
Leng, C. W. 1902. Revision of the Cicindelidae of boreal America. Trans. Amer. Entomol. Soc. 28:93-186.
Stamatov, J. 1972. Cicindela dorsalis endangered on northern Atlantic coast. Cicindela 4:78. U. S. Fish and Wildlife Service. 1993. Northeastern Beach Tiger Beetle (Cicindela dorsalis dorsalis Say) Recovery Plan. Hadley, Massachusetts. 50 pp.