Montana Field Guide

The following is taken from Wallis (1961), Graves and Brzoska (1991), Knisley and Schultz (1997), Kritsky and Horner (1998), Leonard and Bell (1999), Acorn (2001), and Pearson et al. (2015). The body length is 11-16 mm and is extremely variable in size. The color above is variable, from reddish-brown to black or green. Maculations are complete in the subspecies occurring in Montana, usually moderate to wide and distinct, a long oblique shoulder (humeral) maculation (thick or thin) running toward the midline with the rear tip not expanded, a white line along the outer margin of the elytra is lacking. Ventral surfaces are blue to green, purple, or black on abdomen, often with copper on thorax, red-purple on the head. 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 found every month of the year except December, but mostly April-May and again September-October (Graves and Brzoska 1991, Knisley and Schultz 1997, Leonard and Bell 1999, Larochelle and Larivière 2001, and Pearson et al. 2015). April to September in Nebraska (Carter 1989), late March to late October in Colorado (Kippenhan 1994). In Montana, at least some adults are active every month from mid-March to late September (Hendricks and Roedel 2001, Hendricks and Lesica 2007, Winton 2010, Nate Kohler personal communication, and 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. Of the 13 currently recognized subspecies, two occur in Montana: C. t. kirbyi, and C. t. vibex (=borealis). Validity of subspecies designations are tentative and in need of reevaluation (Kritsky and Horner 1998, and Pearon et al. 2015).

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 occurs in a wide variety of habitats including banks and mud flats of creeks and rivers, dry lake beds, tidal flats, roadside ditches, packed gravelly-sandy roads near water, open ground (clay, mud or sand), old fields, stubble fields, saline and alkali flats, blowouts, sand pits, in prairie grasslands, forest trails and roads (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, documented habitats include sedge-grass sand flats, hard-packed gravelly-sandy roads near water, along creeks and ditches, saline/alkali flats, riparian dunes, sandy blowouts, sand pits, 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 in the field feed on ants, libellulid dragonflies, beetles (carabids, curculionids, elaterids), and small wasps. In captivity, ants, caterpillars, small crickets, flies (drosophilids, muscids), and lean meat. Adults in the field feed on ants, flies, grasshoppers, cutworms, aphids, bees, small beetles, other small insects and probably spiders; in captivity ants, bees, beetles (carabids, chrysomelids, tenebrionid larvae), house flies, small crickets, small earthworms, and lean meat (Larochelle and Larivière 2001).

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 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, and Knisley and Schultz 1997). Eastern and northern populations of Cicindela tranquebarica have a broad range of ecological tolerance (eurytopic), those in the desert southwest a narrower range of tolerance (stenotopic); the subspecies present in Montana are eurytopic. Adults are mostly diurnal, sometimes attracted to artificial lights at night, and solitary or gregarious (Larochelle and Larivière 2001). Adults can tolerate hypoxia from submersion in water for more than 20 hours, third instar larvae for more than 60 hours (Brust and Hoback 2009). Adults often bask and stilt on warm soil, regulate body temperature at 33-38°C, active throughout the day from 25-38°C, during the hottest part of the day shuttle between moist and dry areas or seeks shade of small plants, hide at night and during cool, cloudy, or rainy days in self-made burrows in sandy mounds, river banks, paths, sometimes under wood or stones. Predators include toads, birds (woodpeckers, crows, flyctachers), and theridiid spiders, probably also asilid (robber) flies. Larval parasites 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. Emits a characteristic odor (presumably benzaldehyde) when handled (Vaurie 1950, Ferris 1969, Schultz and Hadley 1987, Knisley and Schultz 1997, and 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 is 2 years in most areas, with third instar larvae and teneral adults overwintering (Larochelle and Larivière 2001, and Pearson et al. 2015). Mating is reported May to July, coition lasts 4-15 minutes; interspecific copulation noted with C. purpurea and C. scutellaris (Larochelle and Larivière 2001). Females oviposit eggs underground during the day in April and May while burrowing up to depths of 60 cm (but usually < 30 cm) (Brust et al. 2012) 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, sometimes aggregated in groups of several hundred. Pupation occurs July-August, tenerals (fresh adults) appear July-September then overwinter, 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 10-11 months (Criddle 1907, 1910; Shelford 1908, and Larochelle and Larivière 2001). In Montana, mating has been observed at 6660 ft (2030 m) elevation during mornings in late May to at least early July (Hendricks and Roedel 2001, Hendricks and Lesica 2007, and Hendricks personal observation) on sunny days when air temperatures were 18-21°C.

Not considered rare or in need of special conservation management overall (Knisley et al. 2014) but two subspecies with very limited distributions in California are vulnerable to extirpation. 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 also a useful tool for maintaining a variety of successional conditions (Winton 2010).