Wednesday, February 1, 2012

The Beach Tiger Beetle

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. 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. 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.

Status: Data Deficient by IUCN, but listed as endangered by Maryland and Massachusetts. Threatened status has been proposed by Virginia.

Population: Today, it is extinct in 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.

Biology: 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. 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. 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. 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. Larvae grow in size and burrow deeper, going from 4 to 6-7 to 9-14 inches into the sand.

Threat: 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, birds and spiders. Larvae are preyed upon by parasitic, wingless wasps, which lay their eggs on the tiger beetle larvae. The larval wasps develop by eating the larval tiger beetles. 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.

Conservation Underway: 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. The Service's Virginia Field Office is working with Bavon Beach property owners and other partners to develop and fund the construction of a breakwater system with beach and dune replenishment and restoration. The system would help increasing habitat for the tiger beetle.