Callophrys [Mitoura] spinetorum
Thicket Hairstreak

Family Description:
Alternate Common Name:
Blue Mistletoe Hairstreak.
Note: This species includes a subspecies, millerorum, which occurs in Mexico.

Caterpillar: The caterpillar varies in appearance, but generally is green with a lighter band of brownish green along the back. The body is "bumpy," and the bumps are colored reddish orange to brown and edged with white. The sides are striped lengthwise with white. Caterpillars may also be mostly green or red; they tend to match the color of their host plant. The average, full-grown length is 7/8 inch.
Adult: This is a fairly small butterfly, with a wingspan of 1 to 1 inches. The upperside is grayish blue with no noticeable markings. The underside is reddish to grayish brown and is marked by a thin, white line, edged towards the inside with black, which spans both the fore- and hindwing. On the hindwing, the line becomes wavy, forming a "W", near the bottommost edge. Additionally marking the underside, there is a curved row of black dots near the edge of the hindwing. As with most hairstreaks, a thin "tail" extends from the hindwing.

This species ranges from southern British Columbia and Alberta south to southern California and into Mexico. In the U.S., it extends as far east as Colorado and New Mexico. It occurs through much of Idaho, but predominantly in the central portion of the state.

Typical habitat includes coniferous and mixed forests and desert canyons.


Caterpillar: Caterpillars feed on the external parts of dwarf mistletoes (Arceuthobium spp.), a parasitic plant that lives on a variety of conifers.
Adult: Butterflies drink flower nectar, often from flowers belonging to the sunflower family (Asteraceae).

There is one generation of caterpillars through most of its range while there may be several in the south. Each undergoes five stages of growth, called instars. The caterpillar is equipped with a honey gland, also known as a dorsal nectary organ, which emits a sugary solution agreeable to ants. The ants feed on the solution and in turn protect the caterpillar from predators. Pupae overwinter in a physiological state called diapause in the mass of plant growth of the host tree, caused by the mistletoe’s presence. Adults generaly fly from March through October, with most adults in the northern part of its range appearing in June. The thin "tail" on each of the hindwings of adults is thought to mimic insect antennae and thus misleads bird predators into biting at the wrong end and only getting a mouthful of wing, while the butterfly escapes in the other direction.

Males perch to wait for receptive females. Females lay eggs singly on mistletoes.

Idaho Status: Unprotected nongame species.
Global Rank: G5; populations are widespread, abundant, and secure.

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Opler, P. A., H. Pavulaan, and R. E. Stanford. 1995. Butterflies of North America. Jamestown, North Dakota, USA: Northern Prairie Wildlife Research Center Home Page. (Version 05Nov98).

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Stanford, R. E. and P. A. Opler. 1993. Atlas of Western U.S.A. Butterflies (Including Adjacent Parts of Canada and Mexico). Published by authors, Denver, Colorado, USA, 275 pp.