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Montana Field Guide

Montana Field Guides

A Mayfly - Ameletus sparsatus

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Native Species

Global Rank: G4G5
State Rank: SNR

Agency Status

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General Description
This large swimming mayfly species is associated with medium to large sized, moderate gradient, cool-coldwater rivers (Intermontane River Aquatic Ecological System) with cobble riffles, some gravels and silted pool & side channel areas with aquatic vegetation areas.

Diagnostic Characteristics
Adult morphology: Body length: 10-12 mm. Eyes have green pigmentation in living males. Mesonotum is yellow with light brown at the periphery. Mesotergum is yellowish with brown longitudinal streaks (based on a preserved female imago specimen from Alberta, Canada). Fore wings transparent with some cross-veins surrounded with smoky brown, giving them a speckled appearance. Specimens from British Columbia, Alberta, and Colorado have well-defined dark patches on the fore wings (four larger patches in a preserved female imago from Alberta). Abdominal sternite 2 has a pair of C-shaped markings; ganglionic markings may be visible on sternites 7 and 8 (Zloty 1996, Zloty and Pritchard 1997). This species is likely to be confused with A. amador and A. falsus. The male genitalia resemble those of A. imbellis (Zloty 1996).

Larval morphology: Body length: 10-11 mm. Antennae mostly brown with segments 2-4 pale. Labrum is pale with brown ovoid patch proximally. The dorsal surface of the front femora has numerous long spines and a fringe of sparse and relatively short hairs. The anterior surface of the front femora is yellow with a broad brown patch at the middle that does not extend onto the ventral surface. Posterolateral spines on abdominal segments 8-9 very long. Ganglionic markings sometimes visible on sternite 8 (Zloty and Pritchard 1997). Based on a large series of larvae from the Henrys Fork, eastern Idaho, younger larvae were pale and incompletely marked. All larvae, regardless of age, showed distinct subcutaneous ganglionic markings (Jensen 1966).
Larvae of A. sparsatus could be confused only with larvae of A. cooki and A. suffusus.

Range Comments
Rangewide, Ameletus sparsatus is known to occur in Colorado, Montana, Idaho, Alberta, and British Columbia.
In Idaho, Ameletus sparsatus has been reported from seven counties including Valley County in west-central Idaho; eastward to Blaine, Custer, and Lemhi counties; and southeasterly to Fremont, Bonneville, and Bannock counties (Jensen 1966, Newell and Minshall 1978). Jensen (1966) reported specimens from large and mid-sized rivers including the Henrys Fork, Salmon River, and Big Lost River; and from smaller drainages including Rapid Creek (Bannock County), Lake Fork Creek (Valley County), and Pine Creek (Bonneville County). A more recent publication by Zloty (1996) and the even more recent World Wide Web-based distribution map by Kondratieff (2000) agree that A. sparsatus is known from only two Idaho counties: Blaine and Valley.

In Montana, Ameletus sparsatus has been reported from the Madison River in Gallatin County adjacent to Yellowstone National Park and most recently in the Bitterroot River (Bioblitz 2009). Unfortunately, the identification key to Ameletus species has not been used by bioassessment agencies, and thus we have very few species-level ID’s. This species could potentially occur in mid-sized to larger river systems in the other counties in the southwestern part of Montana, but species-level records are just not available.

Observations in Montana Natural Heritage Program Database
Number of Observations: 7

(Click on the following maps and charts to see full sized version) Map Help and Descriptions
Relative Density



(Observations spanning multiple months or years are excluded from time charts)

This species is associated with larger, moderately flowing rivers and streams (Jensen 1966). Zloty and Pritchard (1997) found larvae in third- or fourth-order streams that had abundant littoral vegetation. The trophic relationships of larvae of Ameletus spp. include scrapers and collectors-gatherers (detritus, diatoms) (Merritt and Cummins 1996).

Reproductive Characteristics
In Alberta, adults of this species emerge from mid-July to mid-August (Zloty and Pritchard 1997).

A. sparsatus is included in the Idaho Comprehensive Wildlife Conservation Strategy (2006) as a Species of Greatest Conservation Need because it is a "species lacking essential information pertaining to status." In Montana this species has stayed off the SOC list due to lack of reliable species records or information; further investigation is required. The Idaho distribution remains in question inasmuch as recent documentation (Zloty 1996, Kondratieff 2000) reports this species from only two Idaho counties whereas earlier research by Jensen (1966) recorded specimens from seven Idaho counties. The reason for the discrepancy is unknown, and the distribution recorded by Jensen (1966) apparently cannot be verified without revisiting the locations reported in his thesis.

Threats or Limiting Factors
Specific threats to Idaho and Montana populations of A. sparsatus have not been identified. In general, mayfly populations are affected by changes to aquatic habitat, such as alteration of flow patterns, streambed substrate, thermal characteristics, and water quality.

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Citation for data on this website:
A Mayfly — Ameletus sparsatus.  Montana Field Guide.  .  Retrieved on , from