Midwestern salmonfly

Conservation Status

IUCN Red List

not listed

NatureServe

N5 - Secure
SNR - Unranked

Minnesota

not listed

Description

Midwestern salmonfly is a large, dark brown, giant stonefly. It is common in the Midwest from Minnesota and Wisconsin south to Kansas and Indiana.

Adults are 1½″ to 2½″ (38 to 64 mm) long. The body is soft, elongated, and flattened. Females are larger than males.

The head is rounded in front, narrows slightly in the rear, and has a thin, bright orange, rear margin. There are two large compound eyes at the side of the head and three simple eyes (ocelli) in a triangle on top of the head in the middle. The antennae are long and thread-like, and have many segments. The mouthparts are vestigial.

The exoskeletal plate covering the thorax (pronotum) is highly sculptured. It is dark brown with a thin, bright orange, longitudinal stripe in the middle. There are also three bright orange spots at the base.

There is a pair of sensory appendages (cerci) at the end of the abdomen. On males, on the sternite on the ninth segment (S9) is split at the into two lobes, and the tips bordering the notch are curved downward. On females, the rear margin of S8 has a small rectangular notch in the middle.

There are two pairs of membranous wings. The hindwings fold flat over the body fan-like and cover most of the abdomen. It has many prominent veins and a large anal lobe. The forewings are narrower and longer than the hindwings. It also has many prominent veins, including a series of cross veins between the media vein (M) and the cubitus vein (Cu) and between the first cubitus vein first branch (Cu₁) and second branch (Cu₂). The are also two rows of two rows of cross veins in the anal area and a row of cross veins between the costa (C), the vein at the leading edge of the wing, and the subcosta (Sc).

The third segment (femur) and fourth segment (tibia) of each leg is robust. There is a pair of claws at the end of each leg.

Size

Total length: 1½″ to 2½″ (38 to 64 mm)

Similar Species

American salmonfly (Pteronarcys dorsata) adults are distinguished from Midwestern salmonfly by the shape of the plate (sternite) on the underside of an abdominal segment. On males, the tips bordering the notch on S9 are straightish, not curved downward. On females, the rear margin of S8 is not notched, and sometimes there are two small projections (bumps) extending rearward.The ranges of the two species overlap completely in the east, but in Minnesota, Pteronarcys dorsata is mostly restricted to five northeastern. However, disjunct populations have been recorded extending down clean cold-water river corridors, including in Wabasha County.

Habitat

Cool, small to medium-sized streams

Ecology

Season

April to June

Behavior

Nymphs move very slowly. When disturbed they will pretend to be dead. Adults are poor fliers and when disturbed they will run rather than fly away. They are sometimes found far from water. They are active at night (nocturnal) and are attracted to lights.

Life Cycle

Nymphs live in well aerated water and take 2 to 3 years to develop. Adults emerge from April to June and live for only 2 to 3 weeks.

Larva Food/Hosts

Particulate plant matter

Adult Food

Adults do not feed

Distribution

Sources

7, 24, 30, 82, 83.

Biodiversity occurrence data published by: Minnesota Biodiversity Atlas (accessed through the Minnesota Biodiversity Atlas Portal, bellatlas.umn.edu. Accessed 5/27/2026).

Pteronarcys pictetii Hagen, 1873 in GBIF Secretariat (2023). GBIF Backbone Taxonomy. Checklist dataset https://doi.org/10.15468/39omei accessed via GBIF.org. Accessed 5/27/2026.

Kondratieff, Boris C. and Richard W. Baumann (coordinators).  2000.  Stoneflies of the United States.  Jamestown, ND: Northern Prairie Wildlife Research Center Online.  http://www.npwrc.usgs.gov/resource/distr/insects/sfly/index.htm (Version 12DEC2003). (archived)

Harden PH, Mickel CE. 1952. The stoneflies of MInnesota (Plecoptera). Technical Bulletin of the Minnesota Agricultural Experimental Station 201. 84 pp.