Habroscelimorpha dorsalis dorsalis (synonym Cicindela dorsalis dorsalis), commonly known as the northeastern beach tiger beetle, is the largest subspecies of eastern beach tiger beetle species (Habroscelimorpha dorsalis). In 2012, Cicindela dorsalis dorsalis was reclassified under the name Habroscelimorpha dorsalis dorsalis, but the names are used interchangeably in recently published literature.U.S. Fish and Wildlife Service, Virginia Field Office. (2019, August 28). 5-Year Review of the Northeastern Beach Tiger Beetle. Retrieved April 17, 2020, from https://ecos.fws.gov/docs/five_year_review/doc6121.pdf As its name suggests, the northeastern beach tiger beetle dwells along the U.S. northeast coast in small sand burrows. The beetle is diurnal and can be spotted by its light tan color with dark lines and green hues on its thorax and head.
The northeastern beach tiger beetle is not only an important part of the delicate coastal food web, but can serve as an indicator of beach integrity and quality. The beetle is highly susceptible to abundant human activity and beach erosion. In 1990, the northeastern beach tiger beetle was listed as “threatened” under the Endangered Species Act (ESA) due to massive population declines throughout its range.
Taxonomy There are four subspecies of Cicindela dorsalis: Cicindela dorsalis media, Cicindela dorsalis dorsalis, Cicindela dorsalis saulcyi, Cicindela dorsalis venusta. Cicindela dorsalis dorsalis is the only subspecies to be listed under the ESA.U.S. Fish and Wildlife Service. (n.d.). Listed Animals. Retrieved April 19, 2020, from https://ecos.fws.gov The northeastern beach tiger beetle only overlaps in range with Cicindela dorsalis media, which occupies the southeast coast of the U.S. ranging from Maryland to Florida.Knisley, C. B. (2011). Anthropogenic disturbances and rare tiger beetle habitats: benefits, risks, and implications for conservation. Terrestrial Arthropod Reviews, 4(1), 41–61. doi: 10.1163/187498311x555706
Physical description The northeastern beach tiger beetle is one of the physically larger subspecies of Cicindela dorsalis with a body length if roughly . Its hardened forewings, also called elytra, acquire varying shades of white and tan. The northeastern beach tiger beetle has wings hidden under these elytra. The beetle has large white and black jaws, long antennae, and long legs that allow them to move quickly across hot sand.U.S. Fish and Wildlife Service, Chesapeake Bay Office. (1994, September 29). Recovery Plan for the Northeastern Beach Tiger Beetle. Retrieved April 17, 2020, from https://ecos.fws.gov/docs/recovery_plan/940929b.pdf
The body of this species, including the thorax and bronze-colored head, displays chestnut-colored lines, and sometimes patches of green coloring. Elytra of older beetles tend to be a lighter, whiteish color due to friction with sand particles. Even in the larval stages, the northeastern beach tiger beetle possesses large jaws in order to efficiently catch prey. Larvae also have small hooks that extend from their abdomen in order to grasp the side of their burrows. This prevents the larvae from being lifted out of their burrows when they catch prey. However, the larvae lack a hard cuticle, which makes it difficult to survive outside their burrows in hot summer months.U.S. Fish and Wildlife Service. (n.d.). Status of the Species Rangewide: Northeastern beach tiger beetle. Retrieved April 17, 2020, from https://www.fws.gov/northeast/virginiafield/Status/NBTB.htm
Ecology and behavior
Diet The northeastern beach tiger beetle remains an invertivore throughout its lifecycle—meaning the beetle only preys on invertebrates such as small amphipods, flies, or other beach arthropods. Adult beetles actively hunt their prey as well as scavenge on dead prey, such as washed up fish and crabs on the shoreline. The immature larvae wait in their burrows for passing prey, primarily small arthropods. The northeastern beach tiger beetle uses its long, sharp mandibles in order to catch their food and crush it with lightning speed, hence its common name: “tiger” beetle.
Predation Predators of the northeastern beach tiger beetle include wolf spiders, asilid flies, and birds. These account for about 6% of adult beetle mortality. A decline in northeastern beach tiger beetle populations disturbs the balanced beach ecosystem as beetle predators encounter food scarcity, and populations of small amphipods and flies increase with fewer predators like the northeastern beach tiger beetle.
Reproduction The northeastern beach tiger beetle begins its mating season as early as June, and the season lasts until late July. The female beetle lays eggs in shallow nesting pits, which are usually about below the surface of the beach. In order for a site to be considered a “breeding site,” the beach must have a width of at least ( wide is preferred), length of at least , and a population of at least 30 adults. On beaches with these conditions, it can be assumed there are larvae present. Depending on the sand’s moisture, the larvae will hatch from their eggs after approximately 12 days. The larvae then dig a burrow to develop in and undergo three life “stages” (more information under Life History).
Life history The northeastern beach tiger beetle relies on warm, sunny days to thermoregulate its body temperature—their bodies must be kept at high temperatures to maximize their predatory ability. Given this requirement, the adult beetles emerge around mid-June and peak in abundance in July. Within two weeks after emergence from their larval state, the beetles remain in close proximity to their burrows. After peak abundance in July, dispersal becomes more common, and adults move about from their original burrow spot.
Adult beetles are most active during the day, but display nocturnal activity on warmer nights. When active during the day, adult beetles can be found close to the water’s edge feeding, mating, and absorbing the sun. At night, it is common for females to sit at the bottom of their vertical sand burrow, while the males are positioned to guard the top of the hole. As the temperatures drop in the fall, the adult beetles die off. Larvae, however, are able to seal up their burrows and hibernate for the winter months.
Larvae can be classified into three developmental stages, also called “instars”. Between each stage, the larvae grow bigger and expend more energy. The first-instar larvae emerge from their eggs in late July and early August. They reach the second instar by September, and reach the third instar by mid-March. At this time, some of the larvae develop into adult beetles by June in the same year that they reach their third larval instar. However, it is common for larvae to remain in this third instar for an additional year and emerge as adults the following June. Larvae closest to the water’s edge develop faster given the higher abundance of prey and increased water exposure. Throughout their development, larvae almost exclusively remain in the same burrow. However, larvae have been known to move burrow sites when disturbed or if prey is scarce. Larval activity varies with temperature, moisture, and tide levels—larvae are extremely susceptible to hot, dry conditions and will remain inactive during the summer. Larvae are most active during the fall and spring.
Habitat
Habitat description As evident by their name, the northeastern beach tiger beetle lives exclusively along the northeastern U.S. shorelines. These beetles prefer beaches with much diverse vegetation growing in the dune area and need medium-coarse sand to dig suitable burrows.U.S. Fish and Wildlife Service, Virginia Field Office. (2009, March 19). 5-Year Review of the Northeastern Beach Tiger Beetle. Retrieved April 17, 2020, from https://ecos.fws.gov/docs/five_year_review/doc2372.pdf The top of the burrows appear as perfectly circular holes. As the beetle larvae develop, their burrow depths increase. A burrow for a first instar is roughly , that of a second instar is , and that of a third instar is . Adult burrows are about deep. The further a larval burrow is from the water’s edge, the deeper the larvae must dig for moist conditions.Knisley, C. (1987). Habitats, food resources, and natural enemies of a community of larval Cicindela in southeastern Arizona (Coleoptera: Cicindelidae). Canadian Journal of Zoology, 65(5), 1191-1200. doi:https://doi.org/10.1139/z87-184 In areas that experience frequent and harsh storms, larvae move further up the beach and into the high tide drift zone. Larvae can survive in a flooded burrow for only three to six days.
Habitat destruction is a significant threat to the northeastern beach tiger beetle. As more shorelines along the east coast of the U.S. experience erosion events due to hurricanes, harsh storms, and anthropogenic factors, habitable shoreline is becoming increasingly sparse for beetles. Several studies have shown that beach width is a “critical indicator of suitable habitat”—the northeastern beach tiger beetle prefers beaches that are at least wide.Knisley, C., Drummond, M., & McCann, J. (2016). Population trends of the northeastern beach tiger beetle, Cicindela dorsalis dorsalis Say (Coleoptera: Carabidae: Cicindelidae) in Virginia and Maryland, 1980s through 2014. The Coleopterists Bulletin, 70(2), 255-271. Third instar larvae have been found on much narrower beaches, some less than 2 m wide, since these larvae rarely move from their burrows and beaches erode as the larvae develop.
Historical and present range Northeastern beach tiger beetle populations boomed along the northeast beaches “in great swarms” in the late 19th century and early 20th centuries.Leng, C. (1902). Revision of the Cicindelidae of boreal America. Transactions of the American Entomological Society, 28, 93-186. This beetle inhabited Massachusetts, Rhode Island, Connecticut, New York, New Jersey, Maryland, and Virginia. Starting in the 1920s, scientists began to notice that northeastern beach tiger beetle populations were declining. Currently, the northeastern beach tiger beetle appears to be extirpated (locally extinct) from Rhode Island, Connecticut, New York, and New Jersey.
Critical habitat areas are beaches which have been deemed vital to conserving the northeastern beach tiger beetle species. When the species was listed as “threatened” in 1990, no critical habitat was proposed, and there continues to be no official critical habitat claimed today. However, protected areas have been identified in Virginia and Maryland. Virginia areas include Sandy Point Island, Rigby Island, Bethel Beach, Winter Harbor, Picketts Harbor, and Kiptopeke State Park. Flag Ponds, Maryland is also an area under state protection. In 2015, the Center for Biological Diversity submitted a petition to the U.S. Fish and Wildlife Service (USFWS) to designate approximately 42,955 acres of northeastern coast as critical habitat.Center for Biological Diversity. (2015, January 22). Petition to the U.S. Department of Interior and the U.S. Fish and Wildlife Service for Rulemakings Designating Critical Habitat for Nine Northeast Species. Retrieved April 17, 2020, from https://ecos.fws.gov/docs/tess/petition/756.pdf This included areas within the Chesapeake Bay, New Jersey, Long Island, southeastern Massachusetts, Cape Cod, and Martha’s Vineyard. This petition has not come to fruition.