Taylor et al.

Milbert's Tortoiseshell, milberti (: ): A facultative trogloxene in alpine caves

Steven J. Taylor1, Jean K. Krejca2, Michael E. Slay3, and Terry L. Harrison4

1Illinois Natural History Survey, University of Illinois, 1816 S Oak St., Champaign, IL 61820 USA. Email: [email protected] 2Zara Environmental LLC, 118 W. Goforth Rd., Buda, TX 78610 USA. Email: [email protected] 3The Nature Conservancy, 601 North University Avenue, Little Rock, AR 72705 USA. Email: [email protected] 4Department of Entomology, University of Illinois, 320 Morrill Hall, 505 S. Goodwin Ave., Urbana, IL 61801 USA. Email: [email protected]

Key Words: Arthropoda, Insecta, , Mountain View Cave, Broken Cave, Great Basin National Park, Snake Range, White Pine County, Nevada, USA, trogloxene

Use of caves as a habitat by has been reported for , libatrix (Linnaeus) (Noctuidae)1, grannyʼs cloak moth, Speiredonia spp. (Noctuidae)2,3, the hop vine moth, humuli Harris (Noctuidae)4, guano moths (Tineidae)5,6, and Geometridae (e.g., [Guenee])1,7–9. However, most other Lepidoptera – the , moths and skippers – are almost never thought of as trogloxenes or troglophiles. Milbertʼs Tortoiseshell, (Godart) (Lepidoptera: Nymphalidae: Nymphalinae) is a boreal North American brush-footed , most closely related to the Palearctic butterfly Aglais urticae (Linnaeus)10. It occurs from Alaska to Newfoundland, extending to the south – in the western United States west of the Great Plains – to southern California and New Mexico. In the eastern United States it is less frequently recorded further south than Wisconsin, Minnesota, Michigan, Ohio and west to Pennsylvania and New York11. This butterfly is reported as being a riparian species12,13, and occurs in meadows, roadsides, and clearings14,15. Adults are strong fliers12, and migrate to alpine habitats to forage in the summer16, where they can be common17–19. Nectar sources include phlox and bee plant20, and, in the eastern United States, Burdock, Joe-Pye Weed, and Shrubby Cinquefoil21. Adults return to lower altitudes to overwinter, with eggs being laid at lower altitudes in the spring16. Larvae feed on herbaceous vegetation, especially Urtica sp.14,15,22,23. We have recently completed a bioinventory of caves of Great Basin National Park (White Pine County, Nevada) in which we observed and collected butterflies in two caves located above timberline. In Mountain View Cave (length 16.2 meters, elevation 3413 meters), two specimens of A. milberti were collected on 18 July 2007 from dry bedrock ceiling in the twilight zone, where the

2009 Speleobiology Notes 1: 20-23 20 Taylor et al. temperature was between 2.07 and 15.57 ○C, the relative humidity was between 34.6 and 80.9%, and light was less than 4 lux (the collection was between two stations where the parameters were measured, thus a range is given). Surface conditions were 20.39 ○C, 25.9% relative humidity, and light 94600 lux. In Broken Cave (length 32.9 meters, elevation 3407 meters), one specimen of Milbertʼs Tortoiseshell was collected on 10 July on a dry rock wall and another on 16 July 2007 on a dry bedrock ceiling (Figure 1), with others observed on 16 July 2007. Here the collections were in the twilight zone where on 16 July 2007, air temperature was 8.27 ○C, relative humidity was 48.2%, and light level was 1 lux. Surface conditions on 16 July 2007 were air temperature 18.28 ○C, relative humidity 38.0%, and light 9860 lux. All specimens at both sites were observed to be roosting with wings folded over their dorsum as in Figure 1.

Figure 1. Milbertʼs Tortoiseshell, Aglais milberti (Nymphalidae) roosting on the ceiling of Broken Cave (16 July 2007).

Our study of caves in Nevadaʼs Snake range included multiple visits to 26 caves ranging in elevation from 1724 to 3413 meters, yet we observed A. milberti in only two of these caves, both of which were above timberline. These

2009 Speleobiology Notes 1: 20-23 21 Taylor et al. butterflies were resting on dry bedrock ceilings and walls in the twilight or dark zones of the caves, functioning as facultative trogloxenes. Careful examination of western North American caves above timberline during the period when A. milberti has migrated to the alpine zone to forage should yield additional observations of facultative cave use by this .

Acknowledgements: We thank Gretchen M. Baker, Ben M. Roberts, and Meg A. Horner, all of the National Park Service, for guidance and assistance in all stages of our research in Great Basin National Park. Field assistance at Broken and Mountain View caves was also provided by Christy A. M. Slay, Patrick M O'Brien, and Shawn C. Thomas.

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