Basis for Listing

The sandy stream tiger beetle is known historically from 5 counties in Minnesota: Winona (1920), Washington (1921), Scott (1923, 1962), Fillmore (1965, 1997), and Wabasha (1960-1972), and it was rediscovered in large numbers along the Minnesota River in Scott County in 1997, 2000, and 2001. Habitat loss due to dredging in Winona County, flood control and channel changes in Fillmore County, and trampling of larval burrows by cattle in Wabasha County threaten the species' survival in these areas. The sandy stream tiger beetle was listed as a special concern species in Minnesota in 1996.

  Description

Adult sandy stream tiger beetles are 10-12 mm (0.39-0.47 in.) long, and are dull olive-green to olive-brown with a slender, parallel-sided shape. They frequent sandy shorelines in company with the extremely abundant bronzed tiger beetle (C. repanda), which is about the same size, but which has a much more robust build. The bronzed tiger beetle is also reddish-brown. Close-focusing binoculars are useful in separating these species. The white markings on the wing covers of the sandy stream tiger beetle are much more angular than those of the bronzed tiger beetle. In the hand, the former has a pre-apical notch on each wing cover, placing it in the subgenus Ellipsoptera.

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).

  Habitat

In Minnesota, the sandy stream tiger beetle prefers stream banks and sandbars of very fine sand. Suitable looking areas with coarser sand have not yet produced this species. Thus far in Minnesota, this tiger beetle only occurs in the southeastern forested corner of the state, but in states further south and west it is known to occur along riparian habitats in the prairie (Willis 1967).

  Biology / Life History

Adult sandy stream tiger beetles emerge in the early summer (as early as late June), and begin hunting, mating, and laying eggs. They slowly die-off as summer progresses, seldom occurring beyond mid-August. Habitat alteration by severe spring flooding is a concern, but generally there is enough adjacent habitat along larger rivers for them to survive. Adults have been found a considerable distance up-slope from riverbanks, so they may have dispersal capabilities not yet understood.

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 stream tiger beetle has survived some natural flooding disasters in Scott County, but it is not known how it will respond to human- or cattle-induced disturbances or to potential mating-disruption due to lights from sandbar and/or island beach parties after dark (the species is strongly attracted to lights).

  Conservation Efforts in Minnesota

There is a need for further surveys of sites where the sandy stream tiger beetle was previously found to determine whether it still survives there. Additional surveys along the Mississippi, Minnesota, and other larger rivers are also needed.

  References and Additional Information

Dawson, R. W., and W. Horn. 1928. The tiger beetles of Minnesota. University of Minnesota Agricultural Experiment Station Technical Bulletin 56. 13 pp.

Pearson, D. L., C. B. Knisley, and C. J. Kazilek. 2006. A field guide to the tiger beetles of the United States and Canada: identification, natural history, and distribution of the Cicindelidae. Oxford University Press, New York. 227 pp. + plates.

Willis, H. L. 1967. Bionomics and zoogeography of tiger beetles of saline habitats in the central United States (Coleoptera: Cicindelidae). University of Kansas Science Bulletin 47(5):143-313.