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Montana Field Guides

Two-tailed Swallowtail - Pterourus multicaudata

Native Species

Global Rank: G5
State Rank: S5

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General Description
[From Ferris and Brown 1981; Scott 1986; Opler and Wright 1999; Glassberg 2001; Pyle 2002] Forewing 5.2-6.0 cm. Very large, two tails on each hindwing. Uppersurface yellow to orangish with black border, male forewing with narrow black tiger stripes, female forewing with wider stripes on deeper yellow, hindwing with more iridescent blue in submarginal band around posterior orange spots, eyespot at anal angle may lack black pupil or pupil touches posterior margin of orange spot.

One flight, mostly late May to June in British Columbia, May to June in California, mid-June to early August in Colorado mountains; several flights late April to early August in Colorado foothills and southward; many flights in Texas, February to November (Scott 1986). Mainly April to September (Glassberg 2001). Late may through August in Rocky Mountain states (Ferris and Brown 1981). April to early August in Colorado (Scott and Scott 1978), late March to mid-September in Oregon and Washington (Pyle 2002), late march through late August in Oregon (Warren 2005), May to August in British Columbia (Guppy and Shepard 2001).

Diagnostic Characteristics
Best determined by a combination of very large size, yellow base color with black border on each wing, narrow tiger stripes on forewing (stripes wider in female); hindwing with two tails, extensive iridescent blue in submarginal band around posterior orange spots (more extensive in females).

Species Range
Montana Range Range Descriptions


Range Comments
Southern British Columbia and southern Alberta south to central Mexico, east to western North Dakota and South Dakota, central Nebraska, central Texas (Scott 1986; Opler and Wright 1999; Glassberg 2001); to about 2134 m elevation in the Rocky Mountain states (Ferris and Brown 1981), 1481 m to 2774 m elevation (usually below 2438 m) in Colorado (Brown 1957; Scott and Scott 1978), 26 m to at least 2591 m elevation in Oregon (Warren 2005). In Montana, reported across the state from at least 32 counties (Kohler 1980; Stanford and Opler 1993; FLMNH Lepidopterists' Society database), to at least 1676 m elevation. Common in the south, rare to uncommon in the north (Glassberg 2001).

Observations in Montana Natural Heritage Program Database
Number of Observations: 127

(Click on the following maps and charts to see full sized version) Map Help and Descriptions
Relative Density



(Observations spanning multiple months or years are excluded from time charts)


Foothill slopes and canyons, moist valleys, stream sides, woodlands, parks, roadsides, suburbs, cities (Ferris and Brown 1981; Scott 1986; Opler and Wright 1999; Glassberg 2001; Pyle 2002). Habitat in Montana not described but probably similar.

Food Habits
Larval food plants are native and exotic trees and shrubs, including members of the Rosaceae (Amelanchier, Prunus (several species), Vauquelina), Oleaceae (Fraxinus (several species), Ligustrum (multiple species)), Rutaceae (Ptelea (multiple species)), and Platanaceae (Platanus) (Scott 1986, 1992, 2006; Guppy and Shepard 2001; Graves and Shapiro 2003; Warren 2005; James and Nunnallee 2011). Adults feed on flower nectar (including Aesculus, Agastache, Alcea, Allium, Antirrhinum, Apocynum, Asclepias, Astilbe, Bouvardia, Buddleja, Campanula, Carduus, Ceanothus, Centaurea, Centranthus, Cirsium, Clematis, Crocosmia, Delosperma, Delphinium, Dianthus, Dipsacus, Echinacea, Erysimum, Eupatorium, Euphorbia, Geranium, Helianthus, Hemerocallis, Heracleum, Hesperis, Ipomoea, Ipomopsis, Iris, Jamesia, Liatris, Lobelia, Lychnis, Lythrum, Medicago, Monarda, Penstemon, Petunia, Philadelphis, Phlox, Platycodon, Prunus, Ribes, Rosa, Salvia, Saponaria, Scabiosa, Scrophularia, Silybum, Syringa, Tilia, Verbena, Viola, Zinnea), dung, and mud (Pyle 2002; Warren 2005; James and Nunnallee 2011; Scott 2014).

Reproductive Characteristics
Females lay eggs singly on uppersurface of host plant leaves (Scott 1986, 1992, 2006; James and Nunnallee 2011), producing about 55 eggs during 10 days of egg-laying (Guppy and Shepard 2001). Eggs hatch within 7-10 days, develop from L1 instar to L5 instar and pupae in about 33-42 days. Larvae eat host plant leaves, rest on silk mat on upper leaf surface when not feeding, overwinter (diapause) as pupae on base of trunk or on stems (Scott 1979, 1986; Guppy and Shepard 2001; James and Nunnallee 2011). Males patrol throughout the day along canyon bottoms, forest openings, roads, lake margins, stream banks, foliage barriers, through urban landscapes in search of females (Scott 1975b, 1986; Guppy and Shepard 2001; Warren 2005; James and Nunnallee 2011).

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Citation for data on this website:
Two-tailed Swallowtail — Pterourus multicaudata.  Montana Field Guide.  .  Retrieved on , from