Our species profile for this issue is the Mardon Skipper, Polites mardon.

The Mardon Skipper belongs to a group of butterflies known as the Grass Skippers. All 17 of our Washington state grass skippers use grasses, reeds or sedges as their larval host plants. Grass skippers are typified by their small size) orange and brown coloration, recurved tips on their antennae, and a habit of perching with their forewings held at an elevated angle to their horizontal hindwings. Among the grass skippers, those in the genus Polites have yellow rather than white spots on their ventral hindwings, and generally fly quite close to the ground. Their flight is often relatively weak in appearance, but they can dart away powerfully when disturbed.

Polites mardon is a fairly scarce species with a short flight period at any specific locality. Mardons’ preferred habitat is grassy prairie and savannah openings. Its populations appear to vary significantly from one year to another. In Washington the Mardon Skipper is state-listed as endangered, and is protected by the State Fish and Wildlife Department. Its habitat continues to retract under land use pressures, and BT spraying in the southern Cascades has threatened populations there.

The Mardon Skipper is found only in small, isolated pockets in Washington, Oregon and far northwestern California. In Washington there are two distinct isolated populations—one in the Puget Prairies of Thurston and Pierce Counties, the other in the southeastern foothills of Mount Adams. Because of elevation differences the two populations fly at different times, the lower Puget Prairie populations in May and those near Mount Adams in late June and July. Mardon was previously believed to be found only in Washington, but colonies have now been found in southwestern Oregon and northwestern California.

Polites mardon overwinters in the chrysalis, rendering it ready to emerge and fly relatively early in the spring. After the adults have mated during their relatively short flight period, the female scatters her eggs randomly in the vicinity of the grass host plants, particularly near the narrow-leaved Idaho fescue which grows in bunches on the prairies. On hatching, the early caterpillar instars are pale and rather maggot-like in appearance, but as they mature they become a more handsome dark brown.

The typical skipper “collar” constriction is obvious behind the head in early instars, but diminishes somewhat with growth. The larvae live in nests of grass blades tied loosely together with silk. Early instars eat grass leaves partially through from the side, but later instars eat clear through the tender grass tips, causing much of the blade to fall to the ground uneaten. Pupation occurs in the leaf nest about 40 days after the eggs are laid. The pupa is long and slender, and dark in color. In captivity the pupa may eclose to an adult butterfly the same season, but in nature this is not yet known to occur.

The adult Mardon Skipper is not particularly easy to identify, and may be confused with other Polites skippers as well as the Woodland Skipper. The range of Mardon overlaps only with the Sonoran and Sandhill Skippers in the Polites group. Sandhill (P. sabueti) is easily separated by its “spider-web”-like spots on the ventral hindwing, but the Sonoran (P. sonora) is quite similar. Sonora

has smaller, more crisply separated spots on the ventral hindwing, which diagnostically separates it from Mardon. Finally, Mardon has long, bristly “hairs” (actually modified scales) on the head and body, and rather rounded forewing tips. Both these characteristics give it a different jizz from the Woodland Skipper, Ochlodes sylvanoides, which has pointed forewings and shorter, less obvious “hair” on the head and body. Also, dorsally the Woodland Skipper has a much more distinct dark scent patch, or stigma, on the dorsal forewing of the male.

All photos by Dave Nunnallee

G’num2003Vol4No2