Basis for Listing
The sandy tiger beetle was first located in Minnesota in 1967 in Polk County, and a few additional specimens were collected at the same site up until 1970. No other localities of this species are known in Minnesota. The single known location was revisited in 2000 and 2004, but no individuals were seen. The area was formerly private pastureland with steep, open sand dunes. It is now owned by the City of Fertile and is open to public recreation. The original dunes show evidence of extensive off-road vehicle use, which can destroy larval burrows. Two larger, formerly abundant tiger beetle species still persist at this site in small numbers, but the sandy tiger beetle may no longer occur here, and may be extirpated from Minnesota. The sandy tiger beetle was listed as an endangered species in Minnesota in 1996.
Adult sandy tiger beetles are small, averaging 10-11 mm (0.39-0.43 in.) long. They are mostly white, but have a dark red-brown head and thorax, and a brown stripe along the wing-cover suture. They also have an oblique, slightly elongated brown spot on the posterior third of each wing-cover. Their legs are metallic wine or metallic green in color.
Tiger beetle larvae are mostly white and somewhat grub-like (Pearson et al. 2006). The portions of their bodies that are exposed in their burrow entrances are usually the same color and texture as the surrounding soil surface, allowing them to blend in with the soil (Pearson et al. 2006; R. Dana, Minnesota DNR, pers. comm.). Tiger beetle larvae have eyes with dense photoreceptors that give them detailed focusing ability and three-dimensional visual perception (Pearson et al. 2006).
The sandy tiger beetle has been found on steep, open, blowing sand dunes.
Biology / Life History
Adult sandy tiger beetles emerge in the fall (as early as mid-August), begin hunting until colder weather, and then burrow underground for the winter. They re-emerge in early spring (mid-April), begin mating and laying eggs, and slowly die-off as the summer progresses.
Tiger beetles prey on small insects and other arthropods and are visual hunters. Adults will either chase their prey or wait in a shaded area and ambush prey as it wanders by (Pearson et al. 2006). They often chase their prey in fast, short bursts with brief stops in between runs. These stops are necessary for orientation as tiger beetles can run so fast that they cannot see the prey they are pursuing.
Adults have hind wings that are transparent and they are folded under the elytra (hard front wings) when at rest. When disturbed, tiger beetles may take short, low flights to escape. These escape flights and the ability to run quickly are their main defenses against predators. Tiger beetles are also usually well camouflaged in their environment.
Tiger beetle larvae dig burrows in which they live and secure prey. They are ambush predators that lie in wait in the top of their burrows with their jaws open and their heads and thorax flush with the ground surface, essentially filling the burrow entrance and disguising their presence (Pearson et al. 2006). When prey is within reach, the larvae anchor themselves to the sides of the burrow by 2 pairs of hooks on their lower backs, and quickly leap out and grab the prey with their mandibles. The struggling prey is then pulled back into the bottom of the burrow and eaten. When they are done eating, the larvae carry the indigestible portions of the prey to the top of their burrow and throw it backwards away from the burrow entrance. The larvae also use their burrow for protection, and will retreat into it when they sense danger. Larvae primarily use vision to detect danger, but may also sense vibrations in the ground created by large predators (Pearson et al. 2006). It is not known how deep the larvae burrow to overwinter.
Conservation / Management
The sandy tiger beetle is a habitat specialist that requires protection of dune areas. Management plans prepared for occupied sites should provide for the habitat needs of this species. Off-road vehicle use should be restricted on sites where this species has been documented.
Conservation Efforts in Minnesota
Further survey of the only known location of the sandy tiger beetle in northwest Minnesota is needed to see if this subspecies still survives in the state.