Hungerford's Crawling Water Beetle

Brychius hungerfordi

Description

Hungerford's crawling water beetle is a small (0.2 in or 4.2 mm), distinctive, yellowish brown beetle with irregular dark markings and longitudinal stripes over the elytra, each of which is comprised of a series of fine, closely-spaced and darkly-pigmented punctures. Males tend to be smaller than females.

In Spangler's (1954) original study, specimens ranged from 0.15 in (3.7 mm) in length and 0.07 in (1.9 mm) in width (a male) to 0.17 in (4.35 mm) in length and 0.09 in (2.25 mm) in width (a female). Males are characterized by thickened tarsal segments of the front legs with small tufts of hair on the first three segments. This species can be differentiated from all other Halipilidae in Michigan by the shape of its pronotum (dorsal plate of the thorax), the sides of which are nearly parallel for the basal two-thirds and are widened mid-laterally.

Behavior

Hungerford's crawling water beetle is thought to live longer than one year and to overwinter as larvae in the dense aquatic vegetation at the stream's edge. As with other Halipilidae, larvae probably go through three instar phases and pupate in the moist soil above the water line. Adults and larvae are seldom captured together, and they appear to inhabit different microhabitats in the stream. Adults are more apt to be found in stronger currents, foraging for algae on gravel and stone.

Compared to other Halipilidae, the adults are strong swimmers, and they obtain oxygen by swimming to the surface or crawling to the water line at the edge of the stream. Larvae obtain oxygen directly from the water and are found in association with dense mats of vegetation which offer protection and foraging. The growth form of this vegetative cover may be more important than the plant composition. Both adults and larvae are herbivorous but little is known about their specific dietary requirements or feeding adaptations. However, it is likely that they scrape food material from rocks by grasping with their tarsal claws and scraping with their distally flattened and singled notched mandibles which are slightly medially-cupped. This speculation is based on observations of the beetles crawling from rock to rock stopping occasionally to grip a rock for varying lengths of time.

There is no evidence that this species has a dispersal flight. No adults have been found at black-light stations, and the adults seem unusually reluctant to fly. It is possible that if this species disperses by flying, it is during a very brief period of time in the spring. The primary mode of dispersal appears to be movement within the stream.

Habitat

The east branch of the Maple River, which is the site of the largest population of Hungerford's crawling water beetle, is a small stream surrounded by forest with a partially-open canopy so sunlight reaches the water. The stream is cool (59-68°F, or 15-20°C) with a relatively fast-flowing current and a substrate of limestone gravel and rock. The forest is intact, the beaver populations are healthy, and their dams function to stabilize water levels so the riffles below the dams remain predictable from year to year.

Distribution

Although streams in the Great Lakes states, especially Michigan, Wisconsin and Minnesota, have been extensively surveyed during the past 30 years, no additional populations of Hungerford's crawling water beetle have been discovered. The survey resulted in the discovery of the only known population in Canada.

The largest population presently occurs in the East Branch of the Maple River in a pristine portion of stream on the boundary of the University of Michigan Biological Station. Two smaller populations are known from the East Branch of the Black River, Montmorency County, Michigan; and the North Saugeen River at Scone, Bruce County, Ontario.

Threats

Because adult beetles must swim to the surface for air, they are vulnerable to predation by fish, tad-poles, and other aquatic insects. The warmer summer water temperatures force the trout population to deeper waters in Lake Kathleen, giving the beetles an opportunity to repopulate.

It appears that human activity in or near the habitat may be speeding up the loss of the species. The removal of existing beaver dams upstream poses a significant threat to the beetle: the downstream side of the beaver dams serve as a riffle and aeration site because they retain sediments and organic material, raise water temperature, and modify nutrient cycling, decomposition dynamics, and riparian zone structure and composition.

Potential threats that may result in modification of the species' habitat include certain fish management activities, such as removal or introduction of fish; stream-side logging and heavy siltation resulting from logging, impoundment, bank stabilization with structures that create an artificial shoreline; stream pollution; and general stream degradation. In Michigan, one site has already been impounded by a dam, and the Ontario site has been impounded upstream.

Given the rate of recreational development and the demands for fish, wildlife, and forest management in northern Michigan, unknown populations of Hungerford's crawling water beetle could be easily extirpated before they are discovered, increasing the need to protect existing populations. Because only three populations of this species are known to exist, loss of even a few individuals could severely affect the continued existence of the species.

Although current scientific research has mostly involved capture and release rather than collecting, the species will continue to draw scientific interest and collection should be regulated. Because of the species' rarity, there is the possibility that amateur scientific collections could occur.

Because all three known populations occur immediately downstream from a roadway, accidental events such as a chemical spill, or the cumulative effects of road salt runoff, pose a threat.

Because of its limited numbers, the beetle faces reduced reproductive vigor and the possibility of stochastic extinction.

Conservation and Recovery

At the present time recovery efforts related to these problems are restricted to legal instruments already in force. The Endangered Species Act requires Federal agencies to evaluate their actions with respect to any listed species. The act also prohibits any imports or exports of listed species, or to offer them for sale. Laws also prohibit any malicious damage or removal of species from their habitat. In the case of this species, the Fish and Wildlife Service has not recommended designating Critical Habitat because of the potential of increased pressure put on the species by vandals or hikers.

The most important regulatory control for protecting this species is the issuance of permits that would modify the beetle's habitat.

Contacts

U. S. Fish and Wildlife Service
Regional Office
Federal Building
Ft. Snelling
Twin Cities, Minnesota 55111
http://midwest.fws.gov/

East Lansing Ecological Services Field Office
2651 Coolidge Rd.
East Lansing, Michigan 48823-6316
Telephone: (517) 351-2555
Fax: (517) 351-1443

References

U. S. Fish and Wildlife Service. 7 March 1994 "Endangered and Threatened Wildlife and Plants; Determination of Endangered Status for Hunger-ford's Crawling Water Beetle." Federal Register 59 (44): 10580-10584.