Montana Field Guide

The Meltwater Lednian Stonefly is a small, dark species of extremely cold glacier-fed streams at high elevations in Glacier Park south through the Mission and Swan Ranges of northwestern Montana. Little else is known about its habits or ecology, except that the adults emerge in mid-summer (July-August) and mate during this time.

Lednia tumana lives most of their lives (~1 years) in the water as nymphs (wingless, immature insects) and emerge as winged adults usually in July or August to find a mate and reproduce. Adult Lednia tumana are short lived (probably a week or less), making them difficult to collect at this life stage. They likely have poor dispersal as most stonefly adults are weak fliers.

Adults are 4.5-7.0 mm in length and dark brown with wings nearly as long or longer than the body (Baumann and Stewart 1980, Baumann and Kondratieff 2010). Adults fold their wings over their back and have antenna much longer than their head. Nymphs are a similar length (4.5-6.5 mm) but lack wings and live in streams. Lednia tumana nymphs lack gills and late instar nymphs are darkly colored. Lednia tumana can be separated from Zapada species by the lack of cervical gills.

No migration is noted for this species, they are restricted in range and dispersal.

The larvae are found in first-order small alpine, mountain streams (Newell and Minshall 1976, and Muhlfeld et al. 2011), but only those closely linked to glacial run-off (Giersch 2002). A closely related species, Lednia tetonica, lives in streams with cold water temperatures (<8.5°C) that originate from glaciers. These stoneflies live in streams with meltwater from both surface glaciers and subterranean ice (e.g., rock glaciers). Streams tend to be stable (i.e., low variation in flow, not flashy) with cobble substrate in the alpine zone of mountains (i.e., usually above treeline). One study suggested they can persist in areas after glaciers have melted (Muhlfeld et al. 2020); however, rock glaciers are very common and cryptic features on the landscape that are the source of streams with very cold, and stable conditions (Brighenti et al. 2021).

Stable isotope were used to investigate the diet of a closely related species in the Teton Range, Lednia tetonica. These stoneflies primarily ate biofilm (mixture of bacteria, fungi and algae growing on rocks) and the golden algae, Hydrurus (Jorgenson 2022). The proportion of food items consumed depended on their availability and the type of streams that the stonefly lived in (e.g., surface glacier or rock glacier). These stoneflies ate little coarse particulate organic matter (e.g., leaves; 9% on average) and some animal matter (e.g., predator).

The Lednian meltwater stonefly spends most of their life in the aquatic egg and nymph forms and may complete their life cycles in a single year or in 2 to 3 years. Adults are short-lived and emerge from the water to mate on vegetation along the stream by July or August. Ecologically this species is a cold-water stenotherm that is unable to tolerate warm water temperatures (mean temperture exceeding 10 degrees Celsius, maximum temperture exceeding 18 degrees Celsius) and is generally collected within a few hundred meters of the base of glaciers or snow melt derived streams (Muhlfeld et al. 2011).

Adults are present and presumably mating takes place in July and August (Baumann et al. 1977, Giersch personal communication).

On October 4, 2016 the U.S. Fish and Wildlife Service proposed listing the Meltwater Lednian stonefly under the Endangered Species Act due to primarily to threats to the habitat and range of this species including climate change, loss of glaciers and permanent snowfields, and changes in stream flow and water temperature. On November 21, 2019 a notice was published in the Federal Register that the species' status was determined to be Threatened. Further information on status can be found on the U.S. Fish and Wildlife Service's Species Account

Lednia tumana lives in streams originating from subterranean ice (e.g., rock glaciers) and surface glaciers. Physiological studies of the stoneflies have shown that they can survive high temperatures (e.g., 25°C) for short time periods (Hotaling et al. 2020) and that their supercooling point is below 0°C (Hotaling et al. 2021). This stonefly was reared at five temperatures (1, 4, 7, 13 and 21°C) over a 31-day period. Results suggest that their ideal temperature lies between 1 and 13°C (Shah et al. 2023).