Montana Field Guide

[From Hatch 1938] "Length 2 mm.; piceous, the antennae, elytra, tibiae and tarsi paler; pronotum quadrate, about five-sixths as broad as long, sides bisinuate, anterior angles prominent and acute, posterior angles slightly acute; disc of pronotum uniformly alutaceous, set with fine hairs, with an elevated, slightly sinuate carina extending from base to apex on either side at a distance from either lateral margin of about one-fifth the total width of the pronotum; the surface of the pronotum undulating with an especialy prominent longitudinally oval impresssion on the middle line just in front of the middle and other less prominent impressions at about the anterior third along the lateral marginsand at about basal third just within the lateral carinae and elsewhere; elytra uniformly smooth, shining, set with fine hairs and with about ten longitudinal series of punctures the outer two of which are invisible in dorsal view, the second interval carinate in basal fourth, the fifth interval carinate in about basal three fifths, the seventh interval strongly carinate nearly to apex."

Adults presumably active throughout the year.

Determined by a combination of the sculpture of the pronotum (neither smooth nor with a transverse impression between the lateral carinae) and the pronotum shape (quadrate, 5/6 as long as broad) (Hatch 1938).

Restricted to warm springs, adults are flightless and not known to migrate between sites.

Requires surface flowing warm water with temperatures between 60-84 deg. F; found frequently in muddy areas containing watercress and less of a rocky substrate (Kindschi 1994). These beetles feed on small pieces of algae and diatoms that they scrape from submerged rocks on the gravel bottom and among vegetation. Both Z. thermae and M. browni require warm and flowing surface water with temperatures of 60 to 84° F. They are endemic to Bridger Creek Warm Springs near Bozeman, MT.

Uses mandibles for feeding on small pieces of algae and diatoms, scraping the food from rocks (Kindschi 1994).

Adults are probably long-lived (>1 year); they are restricted in their dispersal capabilities by flightlessness and also by their requirement for thermal water (Brown 1976); it is likely, however, that mature larvae crawl out of the warm spring and pupate near its edge (Hooten 1991).

Little is known of the reproduction habits of these beetles, but sexual reproduction of the adults likely occurs on cobbles during winter low water flow periods, and the females will lay eggs on these cobbles or adjacent vegetation.

Microcylloepus browni is a Montana Species of Concern because they are extremely locally distributed riffle beetles (1 known spring site). They occupy limited spring or seepage habitat (total area=35 m2) in and along Bridger Creek where it flows through the property of the U.S. Fish and Wildlife Service’s Bozeman Fish Technology Center (Technology Center) at the mouth of Bridger Canyon, Montana. The globally rare (G1) rankings are largely due to the single locality that this species is found.

Restricted habitat, future human development upstream in the watershed could affect surface flows of this spring (Kindschi 1994). (Kindschi 1994). Specific threats to populations of Z. thermae and M. browni include habitat alteration from the development of warm water and surface water from Bridger Creek which may have adversely affected habitat; although specific impacts are not documented since water use began more than 100 years ago. Upstream land use activities have potential to become a threat but are not known to be a problem at this time aside from some detectable sedimentation.