Montana Field Guide

Adults are 6.5-10.0 mm in length and brown with wings nearly as long or longer than the body (Baumann and Gaufin 1971). Adults fold their wings over their back and have antenna much longer than their head. Nymphs are a similar length but lack wings and are aquatic (L. Tronstad, personal observation). Zapada glacier nymphs have gills on their neck (cervical gills) and late instars are darkly colored. Zapada glacier can be separated from Lednia tetonica by the presence of cervical gills; however, nymphs of Zapada cannot be identified to species at this stage using body characters.

Zapada glacier lives most of their lives (~1 year) in the water as nymphs (wingless, immature insects) and emerge as winged adults in July or August to find a mate and reproduce (Baumann et al. 1977; L. Tronstad, personal observation). Adult Zapada glacier are short lived (probably a week or less), making them difficult to collect in this life stage. They likely have poor dispersal as most stonefly adults are weak fliers.

Larvae have not been associated with the adults or distinguished from other Oregon Forestfly, (Z. oregonensis) group species, although they share the typical characters of the group: cervical gills simple, unbranched and not constricted past the base. Thus, this species would not be identified to species and left within this species group level by taxonomy labs identifying bioassesment samples. Adults described in Baumann and Gaufin (1971).

Zapada glacier lives in streams with cold water temperatures (<8.0°C) that often originate from glaciers or subterranean ice (e.g., rock glaciers) although in Glacier National Park they also live in a high-elevation groundwater-fed streams (Tronstad et al. 2020; Giersch et al. 2016). These stoneflies live in stable streams (i.e., low variation in flow, not flashy) with cobble substrate in the alpine zone of mountains (i.e., above treeline generally). 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 analysis in the Teton Range estimated that Zapada glacier 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 less coarse particulate organic matter (e.g., leaves; 21% on average).

Adults have been collected in July (Baumann et al. 1977) and early August in the Teton Range (L. Tronstad, personal observation).

On October 4, 2016 the U.S. Fish and Wildlife Service proposed listing the Western Glacier Stonefly under the Endangered Species Act due to primary 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.

Zapada glacier 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). Another stonefly (Lednia tumana) that also lives in very cold water in the area 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).