Montana Field Guide

The following is taken from Wallis (1961), Kippenhan (1994), Kritsky and Horner (1998), Acorn (2001), and Pearson et al. (2015). Body length is 12-15 mm, and variable in size. Color is reddish-brown to dark brown or green above. Maculations are complete and usually wide and distinct, a long oblique shoulder (humeral) maculation running toward the midline with the rear tip not expanded, sometimes with a complete or partial marginal band on the outer edge of the elytra. Ventral surfaces are metallic deep blue-green to purple on abdomen, often with copper on sides of thorax. Hairy forehead with erect setae, short upper lip, labrum short with 3 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, and Leonard and Bell 1999). Adult Cicindela tranquebarica kirbyi found in March-June and again September (Larochelle and Larivière 2001). April to September in Nebraska (Carter 1989), late March to late October in Colorado (Kippenhan 1994). In Montana it probably varies with elevation, from mid-March to late September (Hendricks and Roedel 2001, Hendricks and Lesica 2007, Winton 2010, Nate Kohler personal communication, iNaturalist 2023).

The following comes largely from Wallis (1961), Kritsky and Horner (1998), Acorn (2001), and Pearson et al. (2015). For our region, the long obliquely-descending arm of the shoulder (humeral) maculation on the dark elytra differentiates this species from all others. The Blowout Tiger Beetle (C. lengi) has a longer upper lip and a thicker shoulder maculation near the shoulder itself. The Crimson Saltflat Tiger Beetle (C. fulgida) is smaller, more shiny, and with a thicker shoulder maculation. C. t. kirbyi differs from C. t. vibex (= borealis), the other subspecies of Oblique-lined Tiger Beetle in Montana, by being dark brown above with wide maculations (including a thicker shoulder maculation), instead of dark brown or dark green to black with a relatively thin shoulder maculation. C. t. vibex (= borealis) apparently occurs only west of the Continental Divide, not in the eastern prairies. Validity of several subspecies designations is in need of reevaluation (Sumlin 1976, Kippenhan 1994, Kritsky and Horner 1998, Acorn 2001, Knisley and Haines 2007, and Pearson et al. 2015) although C. t. kirbyi is accepted by all authorities.

Non-migratory but capable of dispersal. When wings are fully developed (macropterous), it is a strong agile flier and fast runner. Can colonize newly available habitats within 20 years (Kritsky and Horner 1998, and 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 tranquebarica kirbyi occurs in a variety of habitats including clay banks and mud flats of creeks and rivers, dry lake beds, saline and alkali flats, blowouts, sand pits, vacant lots, in prairie grasslands and along forest trails, usually near water (Vaurie 1950, Wallis 1961, Ferris 1969, Hooper 1969, Kirk and Balsbaugh 1975, Knisley 1984, Carter 1989, Kippenhan 1994, Acorn 2001, Larochelle and Larivière 2001, Kritsky and Smith 2005, and Pearson et al. 2015). In Montana, has been documented in habitats including sedge-grass sand flats, hard-packed gravelly-sandy roads near water, along creeks and ditches, saline/alkali flats, riparian dunes, sandy blowouts, river sandbars, and old river crossings (Hendricks and Roedel 2001, Hendricks and Lesica 2007, Winton 2010, and Nate Kohler personal communication).

Larval and adult tiger beetles are predaceous. In general, both feed considerably on ants (Wallis 1961, and Knisley and Schultz 1997). Larval Cicindela tranquebarica kirbyi diet is not described but probably includes a variety of small insects and spiders. Adults in the field feed on ants, beetles, aphids, and cutworms. In captivity, they feed on small crickets (Criddle 1907, and Larochelle and Larivière 2001). Adults are likely to feed on a variety of other small insects and spiders.

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, deeper burrows for overwintering. Adults are sensitive to heat and light and most active during sunny conditions. Excessive heat during midday on sunny days drives adults to seek shelter among vegetation or in burrows (Wallis 1961, and Knisley and Schultz 1997). Cicindela tranquebarica kirbyi has a broad range of ecological tolerance (eurytopic). Adults are diurnal, and gregarious (Larochelle and Larivière 2001). Stilts (stands high on legs with head elevated) or hides during hottest parts of the day on high beaches away from water, sometimes occupies burrows on rainy days. Predators of adults not described but probably include birds and robber (asilid) flies. Larval parasites probably include bombyliid flies. Escapes by flying rapidly short distances (3-10 m) undulating from side to side, turns to face pursuer once landing then seeks cover quickly. Wary and difficult to approach (Vaurie 1950, Ferris 1969, Larochelle and Larivière 2001). Associated tiger beetle species include Cicindela decemnotata, C. denverensis, C. duodecimguttata, C. formosa, C. fulgida, C. hirticollis, C. lengi, C. limbata, C. nebraskana, C. (=Ellipsoptera) nevadica, C. oregona, C. purpurea, C. repanda, C. scutellaris, and C. (=Parvindela) terricola (Kippenhan 1994, Larochelle and Larivière 2001, and Kritsky and Smith 2005); C. repanda an observed associate in Montana (Paul Hendricks personal observation).

The life cycle of Cicindela tranquebarica kirbyi is 2 years, with both third instar larvae and teneral adults overwintering (Acorn 2001, Larochelle and Larivière 2001, and Pearson et al. 2015). Little information on many reproductive characteristics, but probably similar to other subspecies (see the full species account). Mating is probably May to August (Vaurie 1950, and Larochelle and Larivière 2001). Females typically oviposit in sites where the water table is near the ground surface, often in moist, sandy soil that is sparsely vegetated and contains some humus. Larval burrows are straight and 22-50 cm deep. Tenerals (fresh adults) appear in August then overwinter and reemerge the following spring to mate. Adults overwinter in burrows 28-61 cm deep in sand, 15-30 cm deep in clay, larvae in burrows 46-51 cm deep. Duration of larval life 12-15 months, of adult life about 11 months (Criddle 1907, 1910, and Larochelle and Larivière 2001). In Montana, mating observed at 6660 ft (2030 m) elevation during mornings in late May to at least early July on sunny days when air temperatures were 18-21°C (Hendricks and Roedel 2001, Hendricks and Lesica 2007, and Hendricks personal observation).

Not considered rare or in need of special conservation management overall (Knisley et al. 2014). Benefits from many man-made habitats, including agricultural fields and pastures, rangelands, sand and gravel pits, clay roads, powerline corridors. Native habitats favored by this species experience vegetation encroachment and stabilization as succession proceeds, especially from shrubs and trees which cast too much shade on larval burrows, and benefit from disturbance that retains a variety of succession conditions. Some colonies (particularly the larval burrows) could be impacted by trampling through livestock overgrazing, but grazing at appropriate times and stocking levels could also be beneficial by keeping vegetation cover more open (Knisley 2011). Prescribed fire is also a useful tool for maintaining a variety of successional conditions (Winton 2010).