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New Jersey Endangered and Threatened Species Field Guide
Northern oak hairstreak
Satyrium favonius ontario
Species Group: Invertebrate
State: Special Concern
The northern oak hairstreak is a small butterfly with a wingspan of approximately 7/8 to 1 ½ inches. The underside of the forewing and hindwing are gray-brown and has black and white, narrow postmedian bands. On the hindwing, the bands form an “M” shape. There is a blue tail spot on the hindwing that is capped by orange and black. There are orange spots on each side of the blue mark capped by black and white bands that approach, but do not touch the “M.” Each hindwing has one tail.
The northern oak hairstreak is distinguished from the southern oak hairstreak (Satyrium favonius favonius) by its duller, less extensive coloring; separate from color, the markings are the same.
It appears similar to the white hairstreak, which is grayer and displays a small white dot on the leading edge of the hindwing. The orange spot is larger on the white hairstreak and touches the “M” shape. It also has a similar appearance to the gray hairstreak, which is grayer and has orange on its postmedian bands.
The northern oak hairstreak larva is pale green and has yellow and green lateral stripes.
DISTRIBUTION AND HABITAT
Oak hairstreak habitat ranges from southern New England down the Atlantic Coast to Florida and west to Illinois and the Gulf Coast. Northern oak hairstreaks are found in the northern part of this range. In New Jersey, reports of northern oak hairstreaks have come from across the state, but are generally rare. The majority of reports come from the southern part of New Jersey.
Oak hairstreaks are generally found in oak forests and their edges. They also inhabit adjacent scrub openings with food plants.
As implied by its name, the primary host trees for northern oak larvae are various oaks (Quercus spp.). Adults feed on the nectar of flowering plants including New Jersey tea (Ceanothus americanus), swamp milkweed (Asclepias incarnata), common milkweed (Asclepias syriaca), meadowsweet (Filipendula ulmaria), and maleberry (Lyonia ligustrina).
The female lays eggs on the twigs of the host plant where they overwinter, and larvae hatch the following spring. The larvae feed on the flowers, catkins, and pollen of the host plant. Once mature, the larvae form chrysalises that appear pale brown with black spots. Adults emerge and have a flight period that lasts from mid-June to mid-July.
CURRENT STATUS, THREATS, AND CONSERVATION
The northern oak hairstreak is recommended for listing as a “special concern” species in New Jersey. This means that the species is especially vulnerable to changes in or destruction of its habitat. As it requires oak trees to lay eggs on, any dramatic declines in oaks would most likely have a negative impact on the hairstreaks. Threats to habitat include clearcutting for timber and suppression of fires that maintain oak forest habitat. Spraying of insecticides used for gypsy moth (Lymantria dispar) control was also found to have a negative impact on northern oak hairstreak larvae.
The main method of conservation is habitat preservation. This includes protection of both oak forests and adjacent clearings with food plants. Use of pest control methods such as Bt and Dimilin should be conservative and well monitored.
In 2015, the New Jersey Endangered and Nongame Advisory Committee recommended a Special Concern status for this species within the state, but no formal rule proposal has been filed to date.
Text written by Kathleen Wadiak in 2015.
- Butterflies and Moths of North America
- Massachusetts Audubon Society
- Massachusetts Division of Fisheries and Wildlife
- New York Natural Heritage Program
- North American Butterfly Association, New Jersey Chapter
Species: S. favonius ontario
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