Basis for Listing
The northern barrens tiger beetle was first observed in Minnesota in 1889 in Cass County. It has subsequently been located in Anoka, Chisago, Crow Wing, Morrison, Pine, Sherburne, Todd, Wadena, and Winona counties. Although widespread, this species occurs in a habitat that is easily destroyed by development. It is abundant in areas where it receives protection. The northern barrens tiger beetle was listed as a special concern species in Minnesota in 1996.
Adult northern barrens tiger beetles are 13-14 mm (0.51-0.55 in.) long, and are usually bright green with a transverse ivory band in the middle of each wing cover. Black individuals have occasionally been collected within the large population at Sand Dunes State Forest, suggesting possible gene-flow between the Minnesota and central Wisconsin (C. p. huberi) subspecies.
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 northern barrens tiger beetle is found in openings and sandy roads through pineries, often with scattered ground cover of mosses and lichens. Jack pine (Pinus banksiana) barrens are ideal habitat for this species.
Biology / Life History
Adult northern barrens 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-May), begin mating and laying eggs, and then 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 two 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 northern barrens tiger beetle occurs in a habitat that is threatened by development, and possibly off-road vehicle use and clearcutting of large areas (Steffens 2005). Further surveys are needed to determine if its distribution is as fragmented as it appears.
Conservation Efforts in Minnesota
Additional surveys are needed to determine the distribution and abundance of northern barrens tiger beetles in central Minnesota. Steffens (2005) has identified a number of sites with potential habitat for this species.