Montana Field Guide

The following is taken from Wallis (1961), Kippenhan (1994), Acorn (2001), and Pearson et al. (2015). Body length is 12-16 mm and generally reddish-copper to blue-green to greenish above. Head and pronotum with contrasting margins of green, often tinged with purple and a purple border around the edge of the elytra. Black individuals occur in many populations, especially in the north and west of the range (up to 40% of a population), with black and green forms interbreeding. White maculations reduced to a short isolated middle line slanting backwards, a thin rear maculation along the posterior tip of the elytra, sometimes with an small white dot just anterior to the rear maculation, some individuals with a humeral dot. Elytral border lacks a white connecting line. Below is metallic, dark green to bluish, sides of thorax coppery, black underneath with purple iridescence in black forms. Forehead hairy, labrum short with three teeth.

Tiger beetle life cycles fit two general categories based on adult activity periods. “Spring-fall” beetles emerge as adults in late summer and fall, then overwinter in burrows before emerging again in spring when mature and ready to mate and lay eggs. The life cycle may take 1-4 years. “Summer” beetles emerge as adults in early summer, then mate and lay eggs before dying. The life cycle may take 1-2 years, possibly longer depending on latitude and elevation (Kippenhan 1994, Knisley and Schultz 1997, Leonard and Bell 1999). Adult Cicindela purpurea audubonii, a spring-fall subspecies and one of the earliest tiger beetles to appear in spring, typically emerges February to early June and late August to October across the range (Carter 1989, Kippenhan 1994, Acorn 2001, Larochelle and Larivière 2001, Pearson et al. 2015). In Montana, adults present at least mid-March to June and late July to mid-October (Nate Kohler personal communication).

The following comes largely from Wallis (1961), Kippenhan (1994), Acorn (2001), and Pearson et al. (2015). Similar in the Great Plains to the Green Claybank Tiger Beetle (C. denverensis) and Common Claybank Tiger Beetle (C. limbalis) both of which have one or two white dots as the shoulder (humeral) maculation instead of none, and the middle maculation is perpendicular to the elytra margin with a definite bend or wave backward instead of a short line that angles backward. The latter species most resembles reddish forms of the Cow Path Tiger Beetle. The middle maculation of the Splendid Tiger Beetle (C. splendida) is usually a short horizontal line, and the head and thorax are green or blue in contrast to the reddish elytra. The Long-lipped Tiger Beetle (C. longilabris) east of the mountains, and Prairie Long-lipped Tiger Beetle (C. nebraskana) could be confused with black individuals of the Cow Path Tiger Beetle but both lack a maculation on the tip of the elytra and have a bald, not hairy, forehead.

Non-migratory but capable of dispersal. When wings fully developed (macropterous), it is a weak flier and fast runner (Larochelle and Larivière 2001).

Adult and larval tiger beetle habitat is essentially identical. The larvae live in soil burrows (Knisley and Schultz 1997). Across the range Cicindela purpurea audubonii is typically an upland species not associated with water. It prefers dry clay or sandy soils in grassland and prairie, openings in sparse vegetation, montane meadows to at least 9500 ft (2895 m) elevation, fields, sandy blowouts, salt and alkali flats, open paths, roadcuts, grassy roadsides, ditches, clay bottoms of washes, eroded banks, sandy beaches, open coniferous forests. Larval burrows are often found in sloping or level clay soil (Vaurie 1950, Hooper 1969, Knisley 1984, Carter 1989, Kippenhan 1994, Acorn 2001, Larochelle and Larivière 2001, Kritsky and Smith 2005). In Montana, habitat includes sand hills and blowouts, sandy wallows, sandy washes, roadcuts, two-tracks, montane trails, paths through grassland slopes and along roadsides, prairie dog towns, saline areas near reservoirs, and open ground near prairie rivers and streams, to at least 6706 ft (2044 m) elevation (Winton 2010, Nate Kohler personal communication).

Larval and adult tiger beetles are predaceous. In general, both feed considerably on ants (Wallis 1961, Knisley and Schultz 1997). Diet of adult Cicindela purpurea audubonii in the field includes ants and beetles (scarabeids). Larval diet not described (Larochelle and Larivière 2001, P. Hendricks personal observation).

Larval tiger beetles live in burrows and molt through three instars to pupation, which also occurs in the larval burrow. Adults make shallow burrows in soil for overnight protection, and deeper burrows for overwintering. Adults are sensitive to heat and light and are most active during sunny conditions. Excessive heat during midday on sunny days drives adults to seek shelter among vegetation or in burrows (Wallis 1961, Knisley and Schultz 1997). Cicindela purpurea audubonii has a broad range of ecological tolerance (eurytopic). Larval burrows are generally scattered, excavated in small bare patches of clay to sandy-clay soils (Larochelle and Larivière 2001, Pearson et al. 2015). Adults are diurnal and become active at about 18°C, active early until late in the evening on hot days, solitary or in pairs, occasionally in small groups. Predators in the field include asilid (robber) flies, bluebirds, carabid beetles in captivity. Wary, and reluctant to fly, but escapes predators or disturbance by flying a few meters like a grasshopper and hiding under grass. Associated tiger beetle species include C. longilabris and C. splendida (Kippenhan 1994, Larochelle and Larivière 2001, and Pearson et al. 2015).

The life cycle of Cicindela purpurea audubonii is 2-3 years (Acorn 2001, Pearson et al. 2015). Mating is March to June. Adult females oviposit from the surface during the day to depths of 7-9 mm, often active after rains and when soil surface is moist (Brust et al. 2012). Egg-laying details are not reported but probably similar to C. purpurea purpurea, as follows. Oviposition occurs several days after fertilization. Eggs are cream-colored, 2 mm long and 1 mm wide, about 50 eggs are laid singly. Eggs hatch about 2 weeks after laying (Shelford 1908). Larval burrows are 8-15.0 cm in length, possibly limited in depth by compact soil where they are found (Pearson et al. 2015). Duration of larval life is not reported but probably similar to C. purpurea purpurea, about 12-13 months (Larochelle and Larivière 2001). Third instar larvae overwinter, with pupation in July. Fresh adults (tenerals) emerge in August and September then overwinter and reach sexual maturity the following spring after hibernation. Adult lifespan is not reported but probably similar to C. purpurea purpurea, about 10 months (Larochelle and Larivière 2001). In Montana, photographed copulating late April to early June (iNaturalist [accessed 28 September 2023], Chuck Carlson personal communication).

Not considered rare or in need of special conservation management (Knisley et al. 2014). Anthropogenic disturbance that retains or creates open conditions (clay roads, paths, powerline corridors) benefits Cicindela purpurea audubonnii. Exotic grasses, such as cheatgrass, could become a problem at local scales where they invade open habitats. Larval burrows could be impacted by trampling through livestock overgrazing or livestock concentrations at water sources, but grazing at appropriate times and stocking levels could also be beneficial by keeping vegetation cover more open (Knisley 2011).