Montana Field Guide

A recent synopsis of Zaitzevia in North America (Brown 2001) concluded that Z. thermae was a subspecies of the more cosmopolitan Z. parvula on the basis of no difference between the two in genitalic morphology, and that other morphological differences (smaller length and width, reduced wings of Z. thermae) were consistent with those seen in other riffle beetle species between typical members in non-thermal locations and those inhabiting thermal springs. However, Brown (2001) also included the caveat that molecular or genetic evidence could support the taxonomic validity of Z. thermae as a full species. Apparently overlooked in the synopsis by Brown (2001) was the unpublished thesis by Hooten (1991), where electrophetic analysis segregated the two species and supported the status of Z. thermae at the full species level, even though Hooten (1991) also noted that the genitalia of the two species were indistinguishable.

[From Hatch 1938] "Length 2 mm.; piceous, the antennae, lergs, elytra, and apical portions of the abdomen paler; antennae short, eight-segmented, the funicle composed of a basal long and four very short segments, the last segment of the antennae forming a well marked club; pronotum widest at about basal fourth where it is nearly as wide as long, apex about seven eighths as wide as base, the sides somewhat arcuate; anterior angles of pronotum slightly prominent and acute, the posterior angles nearly rectangular; pronotal disc smooth, shining, sparsley coarsely puntuate and pubescent, with an opague longitudinal median impression occupying about or somewhat more than its median half, the region of the anterior angles opaque the lateral carinae of the pronotum, bordering an opaque impressed area on their median side; the median basal portion of the pronotum impressed, this impression more or less confluent with the median and lateral opaque impressions; elytra with about nine longitudinal series of punctures, corse at base, finer behind the middle, nearly obsolete towards apex; elytral intervals each set with a series of semierect setae, the fourth, sixth, and seventh intervals carinate, carinae crenulate on top, the fourth interval carinate froma bout basal sixth to beyond apical fourth, the sixthinterval carinate to beyond middle, the seventh interval carinate to beyond apical fourth, the carinae of the sixth and seventh intervals confluent for about basal seventh; the surface of the elytra latarad to the fourth interval sericeous except for a smooth humeral space; apex of elyta serrulate."

Presumably adults active throughout the year.

Distinguished from all other elmids by a combination of 8-segmented antennae, pronotum with median longitudinal impression, lateral carinae of pronotum confined to basal 3/5, elytra sericeous laterad to 4th interval, terminal abdominal sternum pimply and rather narrowly biconic at apex, and male genitalia (aedeagus slender and clyndrical with parameres tighly appressed to penis) (Hatch 1938; Brown 2001); also genetic differences (see Hooten 1991).

Non-migratory. Restricted to a single location.

Requires surface flowing warm water with temperatures between 60-84 deg. F; commonly found securely attached under rocks or clinging to watercress (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 warm and flowing surface water with temperatures of 60 to 84° F; it is likely, however, that mature larvae crawl out of the warm spring and pupate near its edge (Hooten 1991).

Adults may be found in copulation most of the year, and the males cling tenaciously to their mates; it is likely that pupation occurs in late summer and early fall (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.

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

Restricted habitat, future human development upstream in the watershed could affect surface flows of this spring (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.