Basic Information
Common Name: Thorne's Hairstreak Butterfly
Scientific Name: Callophrys thornei
Species Code:
Management Category: VF (species with limited distribution in the MSPA or needing specific vegetation characteristics requiring management)
Occurrence Map
Table of Occurrences
UNR Thorne's Hairstreak Monitoring
Monitoring of the Thorne's hairstreak and mapping Tecate cypress. (1) Conduct occupancy surveys for Thorne's hairstreak adults and juveniles. (2) Characterize habitat associated with Thorne's hairstreak presence. (3) Age trees (by coring) in sampled stands of Tecate cypress. (4) Conduct larval and adult experiments to assess the importance of tree age for Thorne's hairstreak. (5) Analyze data from 2009 and 2010 and prepare final report.

Current Distribution Rangewide

Endemic to San Diego County and occurs exclusively in the vicinity of Otay Mountain, confined to areas where Tecate cypress grows [1].

Known Populations in San Diego County

Within the MSPA, Thorne’s hairstreak is found in MU 3 [2].

List Status

Not listed

Habitat Affinities

Occurs in chaparral ecosystems in southern California and northern Baja California. Dependent on its larval host plant, Tecate cypress (Hesperocyparis forbesii), a closed-coned conifer that occurs on mesic slopes and drainages in chaparral [3]. Tecate Cypress is also an imperiled species [4].

Taxonomy and Genetics

A small butterfly of the family Lycaenidae (Gossamer-wings) and subfamily Theclinae (hairstreaks) [3]. The taxonomic placement of Thorne’s hairstreak has been a topic of debate between species experts for several years. Recently, the taxonomy has changed from Mitoura thornei to Callophrys thornei [5].

Seasonal Activity

Bivoltine (producing two broods per season); first generation emergence in late February through March and possibly early April, depending on winter rainfall [6]. The second generation emerges in late May to early June. The species overwinters in the pupa stage within leaf-litter under trees.

Life History/Reproduction

Females oviposit eggs on newly established Tecate cypress host plants and incubate for 7 to 14 days [3]. Newly hatched larvae closely resemble the terminal twigs they feed upon. Complete larval development usually lasts 26- 35 days. First generation emergence occurs in late February through March. Second generation emergence occurs in June through July [3].

Diet and Foraging

Monophagous during the larval stage and dependent on Tecate cypress for its survival [1]. First generation adults have been observed using Ramona lilac and deerweed. Second generation adults were observed using California and flat-topped buckwheat only [6].


Dispersal behavior is not well known. The species’ small range on Otay Mountain suggests significant limits in dispersal [3]. On Otay Mountain it is confined to places where the larval foodplant, Tecate cypress grows. Although a significant stand of Tecate cypress occurs to the north in Coal Canyon, Orange County, California, and small populations are found to the south in northwestern Baja California, Mexico, Thorne's Hairstreak has not been documented to occur in those localities [7].


Mainly threatened by frequent wildfires, habitat destruction, and global climate change [1, 8]. In the long term infrequent fires are essential to maintain populations of Tecate cypress which enables seed dispersal. [9, 10]

Special Considerations:

In 2003 and 2007, wildfires swept through Otay Mountain impacting both Tecate cypress and butterfly [6]. Cypress experts began to analyze the effects of these large scale fires and gathered to discuss at a symposium in June 2010. The overall conclusion was that even with continuous fires, Tecate cypress will not likely become extirpated. Based on recent research Thorne’s recovery appears to be stable [6].

Literature Sources

[1] Brown, J.W. 1993. Thorne's Hairstreak, Mitoura thornei. Pages 122-123 in: T.R. New, editor. Conservation biology of Lycaenidae (Butterflies). Occasional paper of the IUCN Species Survival Commission No. 8, Gland, Switzerland.

[2] MSP-MOM. 2016. Management Strategic Plan Master Occurrence Matrix.

[3] Brown, J.W. 1983. A new species of Mitoura Scudder from southern California.J. Res. Lepid. 21: 245–254

[4] California Native Plant Society. 2001. Inventory of Rare and Endangered Plants of California (sixth edition). Rare Plant Scientific Advisory Committee, David P. Tibor, Convening Editor. California Native Plant Society. Sacramento, CA. 338 pp.

[5] Shields, O. 1984. Comments on recent papers regarding western Cupressaceae-feeding Callophrys (Mitoura). Utahensis 4: 51–56.

[6] Faulkner, D and Klein, M.W. Sensitive Butterflies of San Diego County Workshop, 2005.

[7] Orsak, L.J. 1977. Butterflies of Orange County. University of California Irvine, Museum System Biology Resource. 4. 349 pp.

[8] Zedler, P.H., C.R. Gautier, and G.S. McMaster. 1983. Vegetation change in response to extreme events: the effect of a short interval between fires in California chaparral and coastal scrub. Ecology 64(4):809818.

[9] Keeley, J.E. and C.J. Fotheringham. 2003. Impact of past, present, and future fire regimes on North American mediterranean shrublands. In Fire and Climatic Change in Temperate Ecosystems of the Western Americas, T.T. Veblen, W.L. Baker, G. Montenegro, and T.W. Swetnam, pp. 218262.

[10] Raloff, J. 1996. Butterfly displacement by climate change? Science News 150 (9)