Butterfly Atlas Species Accounts

Butterfly Atlas data collected from 1986-1990

Oak Hairstreak

Satyrium favonius

Named

J. E. Smith,1797

Taxonomy & Nomenclature

Once known as Northern Hairstreak (Euristrymon or Fixenia ontario) and thought to be distinct from Southern Hairstreak (Fixenia favonius). Taxonomic revision, however, has combined the two entities and they are now considered a single species named for their preferred larval host.

Identification

Wingspan: 1 - 1 1/4". Oak Hairstreak is gray brown above and below. The most distinctive mark is found on the underside of the hindwing where a thin black and mostly white midline forms a large, conspicuous "W". In Massachusetts, Oak Hairstreak may be confused with Gray Hairstreak (Strymon melinus). Fresh specimens of melinus are distinctive, being slate gray above and dove gray below as well as lacking the "W" of Southern Hairstreak. Difficulties may occur, however, with faded and worn specimens as markings become indistinct and both species fade to a dull brown.

Distribution

Central Texas northeastward to the southern terminus of the Great Lakes and east to Massachusetts. Eastward from the Texas Gulf Coast to the Atlantic Coast. Several disjunct populations in the Southwest. In New England restricted to Rhode Island, Connecticut, and Massachusetts.

Status in Massachusetts

Rare and local. Found only in six quadrangles during the Atlas period in a narrow belt extending east from Worcester to Boston and southwest to the southern Blackstone Valley region. The status of Southern Hairstreak has apparently changed little since the late 1800s when Scudder (1889) used phrases like "this rarest of our Theclae" and "no other butterfly confined to our Fauna is so little known." Scudder notes records from Amherst and Waltham. No additional records noted by Farquhar (1934), who mentioned only the Waltham records from Massachusetts. Maximum: 4, 7 July 1992, Foxboro. More were counted in 1992 than all Atlas years.  Oak Hairstreak is listed as a species of Special Concern under the Massahcusetts Endangered Species Act. 

Flight Period in Massachusetts

One flight. Late June to mid July. Extreme dates: 23 June 1994, Broad Meadow Brook Sanctuary (Worcester Co.), T. Dodd; and 26 July.

Larval Food Plants

Oaks (Quercus spp.), including White Oak (Q. alba) and Scrub Oak (Q. ilicifolia) and perhaps hawthorns (Crataegus spp.).

Adult Food Sources

Recorded on New Jersey Tea, Meadowsweet, Yarrow, Common Milkweed, Swamp Milkweed, and Maleberry.

Habitat

Scrub areas with dry, poor soil and sparse vegetation.

Life Cycle

EGG: not described. OVIPOSITION: eggs laid singly on the male, catkin-producing, host plant. LARVA: Pale green with various dark green and yellow lateral stripes; bores into flowers of food plants and also feeds on pollen and young leaves (mature larva). CHRYSALIS: pale brown mottled and spotted with black. OVERWINTERING STAGE: Egg.

Notes

1992 was an exceptional year for Southern Hairstreak in Massachusetts. Between late June and mid July at least eight individuals were found in six locales.

Account Author

Richard Hildreth

Additional Information

Read more on this species at the North American Butterfly Association.