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Montana Field Guide

Montana Field Guides

A Mayfly - Callibaetis fluctuans

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Native Species

Global Rank: G5
State Rank: SNR

Agency Status


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General Description
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Diagnostic Characteristics
Callibaetis fluctuans and Callibaetis pictus can often co-occur. Larvae of C. fluctuans can be differentiated from those of C. pallidus, C. pictus, and C. ferrugineus by having the ventral lamellae of gills 3-6 narrowly joined to the dorsal lamella. Larvae of C. pictus are differentiated from those of C. ferrugineus and C. pallidus by the absence of robust setae on the tibiae and tarsi.

Observations in Montana Natural Heritage Program Database
Number of Observations: 36

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Relative Density



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

Callibaetis is common in lakes, permanent ponds, and slow-flowing portions of streams throughout North America.

Reproductive Characteristics
Adults were collected between May and September and it is likely that more
than one generation occurs per year.

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