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Montana Field Guide

Montana Field Guides

A Sand-dwelling Mayfly - Lachlania saskatchewanensis

Species of Concern
Native Species

Global Rank: G4
State Rank: S1
(see State Rank Reason below)

Agency Status

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State Rank Reason (see State Rank above)
This sand-dwelling mayfly is currently listed as "S1" Species of Concern in MT due to extremely limited and/or rapidly declining population numbers, range and/or habitat, making it highly vulnerable to extirpation in the state. This large river species has probably lost miles of habitat due to dams on the Milk, Tongue, Bighorn, and Missouri Rivers.
General Description
This burrowing (body-type & behavior) mayfly is an inhabitant of large, warmwater turbid rivers with shifting sand/gravel substrates and depositional silted habitat areas. This species is a filtering collector feeder, and has long hairs on its fore-legs to perform this filtering-function.

Species Range
Montana Range Range Descriptions


Range Comments
This species was until recently known only from Saskatchewan (Lehmkuhl 1979). It was recently recorded (discovered) in Montana (MNHP March 2006, Gustafson unpublished data). A preliminary global ranking is given to this species; however, a current faunistic survey being conducted throughout Saskatchewan may yield additional records.

Observations in Montana Natural Heritage Program Database
Number of Observations: 10

(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)

The adult stage of this mayfly flies upstream to lay eggs, but generally does not fly overland to seek out new places.

This species is associated with large, perennially flowing prairie rivers (Large Prairie River AES) with sand-gravel dominated bottoms with cobble riffles.

Lachlania saskatchewanensis is in serious decline in the state probably due to siltation and habitat changes brought on by the long-standing drought and the cumulative effects of dams on its large prairie river habitats in Montana.

Threats or Limiting Factors
Threats to this species include dams and diversions and excessive siltation that smothers their sandy bottom habitats.

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Citation for data on this website:
A Sand-dwelling Mayfly — Lachlania saskatchewanensis.  Montana Field Guide.  .  Retrieved on , from