The Widespread Stone (Perlesta decipiens)

Mar 4, 2015 - 10:01 am

STONEFLIES!!!! IN AUSTIN??? A fly fisherman who day-dreams about speckled trout snapping at a well-named fly rhythmically casted over a river of mountain snowmelt might laugh at the idea of stoneflies living in Austin’s creeks. The laughing would be misplaced though, because there are a few species of stoneflies tolerating the harsh conditions here in Austin. The most common of which is the Widespread Stone (Perlesta decipiens). Measuring only a half-inch in length, Perlesta decipiens is considerably smaller than the 1 ½ inch monsters of the Pacific Northwest, but they are just as awesome by any other measure.

Perlesta decipiens nymph
Perlesta decipiens nymph (photo: Todd Jackson)

Stoneflies are easy to distinguish from other aquatic insects by their two tail filaments, two long antennae, and two pairs of similarly-shaped wing pads. One of the really neat features of stone flies is their gills which can be seen branching out from their thorax near their legs (see photo).

 

 perlesta=
Perlesta decipiens gills (photo: Todd Jackson)

Perlesta decipiens gills
Perlesta decipiens gills (photo: Todd Jackson)

 

Since they require reliable cold, well-oxygenated and relatively clean water, they make great water quality indicators. In fact, when we do find them, these critters are typically in spring-fed streams with high water quality like Barton, Bull and Onion. The adult doesn’t live very long, but you just might see one crawling near a creek if you’re very lucky. They look just like the nymph, but with four long wings (see photo).

Adult Perlesta decipiens
Adult Perlesta decipiens (photo: Whitney Cranshaw, Colorado State University, Bugwood.org - See more at: www.Insectimages.org)

Share