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Montana Field Guide

Montana Field Guides

A Mayfly - Baetis tricaudatus

Native Species

Global Rank: G5
State Rank: S5
(see State Rank Reason below)

Agency Status


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State Rank Reason (see State Rank above)
Ubiquitous and abundant across the state.
General Description
This is our most widespread and abundant mayfly of running waters in the state; it can be found in small forested mountains stream systems to the largest riffle sections of the Missouri and Yellowstone Rivers.

Diagnostic Characteristics
Baetis tricaudatus larvae are distinguished from other Montana Baetis by having three unbanded caudal filaments (tails), dark bilobed markings on the pronotum, and robust setae on the abdominal sterna, paraprocts, and antennal scape and pedicel.

Species Range
Montana Range Range Descriptions


Range Comments
Baetis tricaudatus is the most widespread Baetis in North America, found in almost every state, being absent only from the extreme southeast (Morihara and McCafferty 1979a).

Observations in Montana Natural Heritage Program Database
Number of Observations: 784

(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)

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