Montana Field Guide

The following is taken from Pearson et al. (2015). The body length is 12-16 mm. Coastal individuals tend to be larger than those from montane regions. Color quite variable, especially at higher elevations. Above is brown, green, blue, occasionally black, maculations usually complete but thin, the middle band on elytra typically with a gradual bend toward the midline suture and front portion of the band not concave; below metallic coppery-green to blue.

Tiger beetle life cycles fit two general categories. “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). Cicindela depressula has a spring-fall life cycle. Adults at lower and coastal elevations are active from April to July and August to October, montane populations early May to early October (Larochelle and Larivière 2001, and Pearson et al. 2015). Adults from Idaho near the Montana border have been reported in August and September (iNaturalist 2023).

The following comes largely from Pearson et al. (2015). This species is most similar to the Western Tiger Beetle (Cicindela oregona) which has a middle maculation with a sharp turn or elbow that runs towards the posterior, with front portion of the middle band concave. Two subspecies of C. depressula are recognized: C. d. depressula and C. d. eureka. C. d. depressula, the montane form, is the subspecies present in Montana. It tends to be smaller than the coastal form and is quite variable above, usually green or blue, but brown or black in some areas of the range. C. depressula was once considered a subspecies of C. oregona (Wallis 1961, and Pearson et al. 2015) to which species it is most closely related genetically (Knisley et al. 2008).

Non-migratory but capable of dispersal. When wings fully developed (macropterous), it is a strong 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). Habitat for Cicindela depressula includes coastal riparian habitats, riverbanks and river bars (C. d. eureka), grasslands, alpine meadows, forest clearings, roads and road cuts, trails and parking lots (C. d. depressula), on ground composed of sand, loam, clay, or gravel that is open, bare or sparsely vegetated and sometimes wet. Found up to at least 9850 ft (3000 m) elevation in California, sometimes in disturbed areas formed by melting snow, recent wildland fire, and logging, as well as above treeline in alpine terrain (Larochelle and Larivière 2001, and Pearson et al. 2015). Habitat in Montana not described.

Larval and adult tiger beetles are predaceous. In general, both feed considerably on ants (Wallis 1961, and Knisley and Schultz 1997). The diet of Cicindela depressula is not described (Larochelle and Larivière 2001) but probably small insects and spiders.

Larval tiger beetles live in burrows and molt through three instars to pupation. 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). Cicindela depressula depressula has a wide range of ecological tolerance (eurytopic) as evidenced by the variety of habitats in which it occurs, whereas C. d. eureka has a narrow range of ecological tolerance (stenotopic). Adults are diurnal and solitary to gregarious. They are inactive on overcast and rainy days at higher elevations (Pearson et al. 2015). Predators on adults are not reported, but robber (asilid) flies and birds are likely. Escapes by flying quickly for some distance, and also produces a defensive secretion to deter predators. Other associated tiger beetle species include C. longilabris and C. oregona (Larochelle and Larivière 2001).

Mating is not reported but presumably throughout period of adult activity in early May to early October for C. d. depressula, April to July and August to October for C. d. eureka (Larochelle and Larivière 2001, and Pearson et al. 2015). Mating pairs of C. d. depressula photographed early July to mid-August (iNaturalist 2023). Larval burrows of C. d. depressula are clustered in melted snowpack swales in patches of bare soil among low alpine vegetation at 9850 ft (3000 m) in the Sierra Nevada Mountains of California. Larval biology of C. d. eureka is not described (Pearson et al. 2015).

Not considered rare or in need of special conservation management (Knisley et al. 2014). Management needs are hindered somewhat by a general lack of information or survey effort for this species. Response to wildfire disturbance, increasingly a land management issue at higher elevations in the western mountains, remains unknown. Local disturbance could also be a problem for some populations where larval burrows are damaged or destroyed by trampling from livestock, but grazing at appropriate times and stocking levels could also be beneficial by keeping vegetation cover more open (Knisley 2011).