Thymelicus lineola is a member of the family Hesperiidae, the large worldwide family of butterflies known as skippers. The European Skipperling is in the hesperine or “monocot” skipper subfamily, a group of skippers which feed primarily on grasses. In Washington there are 29 species of skippers, 17 of which are monocot skippers. An Old World species,

T. lineola was introduced to Ontario, Canada around 1910, and to British Columbia in 1960. In 2002 T. lineola was discovered near Blaine, WA by Thea & Robert Pyle, and is now found in much of northwestern Whatcom Co. The preferred habitat is farming areas and open lowlands where large stands of grasses are found. The flight period in our area is based on few records, but adults have been found throughout July. Sometimes common where it has established, males perch on tall grasses and fly out to challenge passersby, while females frequent lower vegetation basking and seeking nectar, especially on Lotus pedunculatus (Big Birdsfoot Trefoil). Food plants in Washington include Phalaris arundinacea (Reed Canary Grass), Phleum pratense (Timothy Hay) and Dactylis glomerata (Orchard Grass), the latter used only sparingly. Allen (1997) reported Holcus lanatus (Velvetgrass) as a host in West Virginia, however we tried unsuccessfully to rear larvae on this grass. Carterocephalus palaemon and Ochlodes sylvanoides are two other monocot skippers whose larvae can be found on Reed Canary Grass.

In mid and late July females lay eggs in strings of up to 20, end-to-end but not quite touching, delicately glued to the concave side of a grass leaf. Eggs “daylighted” in April and May hatch rapidly, while eggs in February hatch very slowly over a prolonged period, suggesting that photoperiod controls hatching in this species. Development from egg hatch to pupation is about 50 days, and the adult ecloses 7 days later. On May 30 wild larvae in 3rd and 4th instars were found on Reed Canary Grass at Lk Terrell when the grass was 12-14 inches tall. Mature 5th instar wild larvae were found at Lk Terrell on June 11. The larvae had constructed nests in the upper third of the plants by pulling a single grass leaf into a neat tube and stitching the edges together with tidy silk cross-ties. Nests are very similar to those constructed by Ochlodes sylvanoides (Woodland Skipper), which were found co-habiting the same plants. Larval feeding is evidenced by grass blades eaten in from one side, usually near the tip, and the tubular larval nests are easily found. The larvae pupate in their tied leaf nests. This species has five larval instars, and throughout growth the larvae are solitary. Thymelicus lineola is single-brooded throughout its range. Concealment appears to be the primary survival strategy. The adults are similar to Oarisma garita (Garita Skipperling), although Thymelicus is pale orange dorsally while Oarisma is much darker. Also the immature stages differ. Thymelicus may also be confused with Ochlodes sylvanoides with which it flies, however sylvanoides has yellow spots on the ventral hindwings. The European Skipperling has currently not been found beyond northwestern Whatcom County, however this species is spreading southward and monitoring of its expansion is needed. Skagit County should be surveyed in mid-late July, with emphasis on stands of Reed Canary Grass, to determine if the species has reached that far south. Thymelicus lineola has reached pest status on hay and pasture grasses in some parts of Canada and the eastern US where it can be abundant. The potential impact on commercial crops of Timothy in Cascadia need study. The harvest and transport of Timothy Hay as a factor in spreading Thymelicus also needs study, as does competition between T. lineola and native skippers such as the Woodland Skipper.

All Photos by Dave Nunnallee

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