Oak Hairstreak Erik Nielson

Oak Hairstreak
Erik Nielson

Insecta (Insects)
Lycaenidae (Blues, Coppers, Hairstreaks, Elfins)
State Protection
Not Listed
Not listed or protected by New York State.
Federal Protection
Not Listed
State Conservation Status Rank
Imperiled or Vulnerable in New York, or Apparently secure - Conservation status is uncertain; could be very vulnerable, or vulnerable, to disappearing from New York due to rarity or other factors, or could be uncommon but not rare in New York. More information is needed to assign either S2, S3 or S4.
Global Conservation Status Rank
Apparently Secure globally – The subspecies/variety is uncommon in the world but not rare; usually widespread, but may be rare in some parts of its range; possibly some cause for long-term concern due to declines or other factors. (The species as a whole is common globally.)


Did you know?

In New York, the northern oak hairstreak occurs in the lower Hudson Valley and on Long Island. It has likely been extripated from the Ithaca area since 1970.

State Ranking Justification

Since the potential habitat is widespread in southeastern New York, and since the species probably spends most of its time in the canopy, it is probably much less rare than records indicate. Nevertheless, the habitat is spotty in heavily developed southeastern mainland New York, although the species could be more widespread on outer Long Island.

Short-term Trends

The short-term trends are unknown, but this species may be increasing with global warming.

Long-term Trends

The long-term trends are unknown.

Conservation and Management


The main threat is habitat loss. Gyspy moth (Lymantria dispar) spraying with chemical biocides such as Dimilin would severely threaten any occurrence. It is likely, but not known for sure, that Bt (Bacillus thuringiensis - a bacterial biological control used on gypsy moth caterpillars) would also be lethal to the larvae, but it is likely that Bt mortality would be lower than from Dimilin. The larvae normally complete feeding well before defoliation of oaks by gypsy moth larvae would be a threat. Collecting is not a threat, as it would be nearly impossible to overcollect this secretive species.

Conservation Strategies and Management Practices

In some cases managers might want to consider making sure there are nectar sources available. Milkweeds and dogbanes should not be mowed during their flowering period, but otherwise the habitat is generally forest that probably needs little management. Unless documented otherwise, it must be assumed that Bt is highly lethal to the larvae and therefore gypsy moth spraying could eradicate populations.

Research Needs

More reserach is needed that would identify which species of oaks the larvae eat and whether or not they have any other special needs. It would also be very useful to document the sensitivity of the larvae to realistic doses of Bt (Bacillus thuringiensis - a bacterial biological control used on gypsy moth caterpillars) such as are applied for gypsy moth suppression. The available evidence for other butterflies in the subfamily Theclinae suggests that this species would be sensitive to Bt (Schweitzer 2004; Wagner et al. 1996), but sensitivity of caterpillars to Bt is very variable, even among species in the same genus (Peacock et al. 1998).



This species is most often found on dry rocky or sandy oak or oak-pine forest. Pitch pine and scrub oak may be present, but this butterfly is not generally found in classic pine barrens habitats. It may also turn up around more mixed forests.

Associated Ecological Communities

  • Pitch pine-oak forest* (guide)
    A mixed forest that typically occurs on well-drained, sandy soils of glacial outwash plains or moraines; it also occurs on thin, rocky soils of ridgetops. The dominant trees are pitch pine mixed with one or more of the following oaks: scarlet oak, white oak, red oak, or black oak. * probable association but not confirmed.


New York State Distribution

The New York State distribution is mostly in the lower Hudson Valley and on Long Island. The distribution also includes the Albany Pine Bush where one was collected in 1979. Historically, it was present in at least the Ithaca area, but according to Robert Dirig there are no records in that area since 1970, after collections in 1890, 1967, and 1970. Since 2000, there have been credible reports from Orange, Westchester, Rockland, and Suffolk Counties. As Shapiro (1974) noted, the habitat is not rare in southeastern New York.

Global Distribution

The original specimen supposedly came from Ontario, Canada. However, since 1900 this subspecies has been found from the vicinity of Boston, Massachusetts (not before about 1980) south though coastal New England, southeastern New York, and then more widely from New Jersey through most of Georgia and west into Texas and Oklahoma. While it does occur in much of the lower Midwest east into Ohio and widely in the southeastern states, this species is unknown from the mountains.

Identification Comments

General Description

An average size brown hairstreak, occurring in early summer, with a green slug-like caterpillar occurring on oaks in the spring. In New York, this is most likely to be confused with the gray hairstreak. The Northern Oak Hairstreak is a much browner species and the adults are illustrated in virtually any butterfly guide.

Characters Most Useful for Identification

Note the inwardly pointed "v" mark next to the largest white spot on the hindwing beneath and the prominent "M" (or "W") formed by the inner most line. These two markings together should be diagnostic. There is never any blue above. Live individuals always land with the wings closed. The flight season is also a clue to species, as this species will only be seen in or near New York in June and about the first half of July.

Best Life Stage for Proper Identification

This should be identified as an adult, but an expert on hairstreaks might be able to identify the larva. See Allen et al. (2005).


Adults seem to come to flowers most often late in the day and are thought to spend most of their time in the oak canopy. Adults occasionally are caught in blacklight traps in places where they are otherwise not known to occur.


The larvae are oak feeders, but exactly which species of oaks they use is largely unknown. They do not seem to be particularly associated with scrub oak, but they might use it where it is available. Larvae feed on the new spring growth only and the adults will visit a number of species of flowers, but are most often seen on common milkweed (Asclepias syriaca) and dogbane(Apocynum sp.). Dale Schweitzer has found them on maleberry (Lyonia ligustrina) flowers in New Jersey.

Best Time to See

The adults occur for less than a month in any given year, from about mid-June into mid-July. They often start a few days earlier than the other single-brooded early summer hairstreaks, but commonly occur with the others. The eggs overwinter on oaks and the larvae feed on the new growth in spring, probably finishing about the first of June in most years. There is only one brood in all parts of the range of this species. The adults visit flowers most often late in the day, usually after 16:00 hours.

  • Present
  • Reproducing
  • Larvae present and active
  • Eggs present outside adult

The time of year you would expect to find Northern Oak Hairstreak present, reproducing, larvae present and active, and eggs present outside adult in New York.

Northern Oak Hairstreak Images


Northern Oak Hairstreak
Satyrium favonius ontario (W. H. Edwards, 1868)

  • Kingdom Animalia
    • Phylum Arthropoda (Mandibulates)
      • Class Insecta (Insects)
        • Order Lepidoptera (Butterflies, Skippers, and Moths)
          • Family Lycaenidae (Blues, Coppers, Hairstreaks, Elfins)


  • Fixsenia favonius ontario

Comments on the Classification

This species is usually placed in the genus Satyrium, currently. Older works considered northern populations (subspecies ontario) as a separate species.

Additional Resources


Allen, T.J., J.P. Brock, and J. Glassberg. 2005. Caterpillars in the field and garden. Oxford University Press, New York. 232 pp.

Brock, J. P., and K. Kaufman. 2003. Butterflies of North America. Kaufman Focus Field Guides, Houghton Mifflin Company, New York, NY 284 pp.

Glassberg, J. 1993. Butterflies through binoculars: A field guide to butterflies in the Boston-New York-Washington region. Oxford University Press: New York. 160 pp.

Glassberg, J. 1999. Butterflies Through Binoculars: The East. Oxford University Press, New York, New York. 400 pp.

Gochfeld, M. and J. Burger. 1997. Butterflies of New Jersey. Rutgers University Press: Rutgers, New Jersey. 327 pp.

Iftner, D. C., J. A. Shuey, and J. V. Calhoun. 1992. Butterflies and Skippers of Ohio. Ohio Biological Survey Bulletin. New Series, Vol. 9, no. 1, xii + 212 pp., 40 color plates.

New York Natural Heritage Program. 2021. New York Natural Heritage Program Databases. Albany, NY.

O'Donnell, J.E., L.F. Gall., and D.L. Wagner, eds. 2007. The Connecticut Butterfly Atlas. State Geological and Natural History Survey of Connecticut, Department of Environmental Protection, Hartford. 376 pp.

Opler, P. A., and A. D. Warren. 2002. Butterflies of North America. 2. Scientific Names List for Butterfly Species of North America, north of Mexico. C.P. Gillette Museum of Arthropod Diversity, Department of Bioagricultural Sciences and Pest Management, Colorado State University, Fort Collins, Colorado. 79 pp.

Peacock, J. W., D. F. Schweitzer, J. L. Carter, and N. R. Dubois. 1998. Laboratory Assessment of the effects of Bacillus thuringiensis on native Lepidoptera. Environmental Entomology 27(2):450-457.

Schweitzer, Dale F. 2004. Gypsy Moth (Lymantria dispar): impacts and options for biodiversity-oriented land managers. NatureServe, Arlington, Virginia. NatureServe Explorer. Online. Available: http://www.natureserve.org/explorer/

Shapiro, A.M. 1974. Butterflies and Skippers of New York State. Search 4:1-60.

Wagner, D.L., J.W. Peacock, J.L. Carter, and S.E. Talley. 1996. Field assessment of Bacillus thuringiensis on nontarget Lepidoptera. Environmental Entomology 25(6):1444-1454.


About This Guide

Information for this guide was last updated on: December 21, 2007

Please cite this page as:
New York Natural Heritage Program. 2021. Online Conservation Guide for Satyrium favonius ontario. Available from: https://guides.nynhp.org/northern-oak-hairstreak/. Accessed October 27, 2021.

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