Back to beetle blogging – I hope everyone enjoyed their holiday break as much as I. One of the tiger beetles that I most hoped to see on my trip to Nebraska and South Dakota last September was Cicindela lengi (blowout tiger beetle). This is another one of the several tiger beetle species confined to dry sand habitats in the central/northern Great Plains (Pearson et al. 2006). Its common name would suggest it prefers sand blowouts, the most barren of dry sand habitats and where the co-occurring C. limbata (sandy tiger beetle) can be found. In reality, it also can be found in slightly more vegetated habitats such as dune margins, sand flats, and sandy roadsides along with the much more common C. formosa (big sand tiger beetle) and C. scutellaris (festive tiger beetle). It can also be found occasionally on sand bars along rivers, where the aptly-named C. lepida (ghost tiger beetle) is likely to occur, and in the northern part of its range it even inhabits boreal coniferous forest along sandy roadsides.

Despite its relatively loose habitat requirements, C. lengi is not a common species. In Nebraska it may be locally abundant (Spomer et al. 2008), and while planning my trip I was fortunate to get a specific locality from Steve Spomer and Matt Brust for one of these localized populations in far northwestern Nebraska. [Happily, that locality was very close to the locality where I would be looking for another priority species for the trip, C. nebraskana (prairie long-lipped tiger beetle)]. The site – a sandy roadside embankment – was characterized by a very fine-grained sand, which Matt Brust tells me the species appears to favor over the coarser-grained sands more typical of the Sandhills to the east. Success did not come easily – when no adults were seen at the site after two consecutive days of searching, I hedged my bets and extracted larvae that I hoped would represent this species for an attempt at rearing them out to adulthood in the laboratory. Persistence paid off, however – a hunch told me to make one more visit to the site after a couple days in the Black Hills, with two adults (and another C. nebraskana!) being my reward.

The individual shown in the above photo was an unexpected surprise. It was captured a day later in the Sandhills proper at a locality where I expected to see not this species, but C. limbata (which I did succeed in finding at a nearby locality – see “Cicindela limbata – epilogue“). When I first saw this individual, I thought it was the ever present C. formosa (pictured below), which it greatly resembles and which, along with C. scutellaris, occurs commonly in suitable sand habitats throughout the Sandhills. Something about the way it flew gave me pause, however, and after capturing and looking closely at it in my hand I realized what it was. Cicindela lengi is distinguished from C. formosa morphologically by its slightly narrower form and longer, narrower labrum, but the quickest field identifier is the obliquely straight humeral marking (“C”-shaped in C. formosa). There are subtle behavioral differences also – both species are alert and quick to fly, but C. lengi lands quickly after a short flight, whereas C. formosa flies further and tends to land with a comical bounce and tumble or two across the sand. Cicindela lengi and C. formosa are not closely related despite their similar appearance – the former is assigned to subgenus Cicindela (Tribonia), while the latter is assigned to the nominate subgenus. The individual pictured above represents the nominate C. lengi lengi – populations north of Nebraska and Colorado exhibit a distinct coppery underside to the thorax and are assigned to subspecies C. lengi versuta, while populations in the southwestern part of its range show broadly coalesced elytral maculations and are assigned to subspecies C. lengi jordai.

REFERENCES:

Pearson, D. L., C. B. Knisley and C. J. Kazilek. 2006. A Field Guide to the Tiger Beetles of the United States and Canada. Oxford University Press, New York, 227 pp.

Spomer, S. M., M. L. Brust, D. C. Backlund and S. Weins. 2008. Tiger beetles of South Dakota & Nebraska. University of Nebraska-Lincoln Special Publication, 60 pp.

In my Lucky 13 post, I featured Cicindela limbata (sandy tiger beetle) from north of Grand Island, near the easternmost edge of the Nebraska Sandhills. This species is restricted to dry sand blow out and dune habitats away from water, thus its distribution in Nebraska largely coincides with that of the Sandhills themselves. Nebraska populations are assigned to the nominate subspecies, which is characterized by extensively developed white maculations on the elytra, with the sutural area and small discal markings metallic green or blue. The whitish areas on the elytra and dense pilosity on the undersurface, along with their habit of digging into the sand during the midday hours, are obvious adaptations for reflecting heat and avoiding the high temperatures that occur in their white sand habitats. In the more eastern areas of the Sandhills, the green sutural areas of the elytra are suffused with a reddish cast (see this photo in Lucky 13), while in populations further to the west no such reddish suffusion is seen. The individual featured in these two photos was found in the western Sandhills (near Hyannis) and is one of the individuals that I dug from their midday burrows (see Sand Hills Success). Had I not been clued into this behavior when I visited this site, I would have left with only the single individual that was seen at the surface. That individual was captured immediately, and further searching for active adults to take photographs of were unsuccessful – until I started digging, that is. Unfortunately, adults that have just been caught or dug out of their burrows aren’t the most cooperative photography subjects, so one of them was kept alive and placed in a terrarium upon my return to St. Louis. (These photos were taken about a week after I returned, and the individual lived for another seven weeks on a diet of 3rd instar fall armyworm and black cutworm larvae. I eventually trained it to grab larvae directly from the forceps – very entertaining indeed! Also, while these photos from the terrarium confines are adequate for illustrating the species, I think they still lack that undefinable spark that is caputured in true field photographs with unmanipulated individuals – compare to this photo).

Cicindela limbata, with its five recognized subspecies¹, has one of the more interesting distributions of North American species (see Pearson et al. 2006). In the main area of distribution, the southernmost populations, distributed through most of Nebraska and adjacent areas of Wyoming and South Dakota, are considered nominotypical. A distributional gap to the north separates these populations from subspecies nympha, which occurs in sand habitats of northern Montana and North Dakota and further northward into the Canadian Prairie Provinces. Individuals from these populations exhibit even greater development of the white maculations but darker intervening areas. Another distributional gap separates nympha from subspecies hyperborea, which (as its name suggests) occurs even further north in open sand habitats in the pine and poplar forests of northern Alberta and Saskatchewan and adjacent areas of the Northwest Territories. Subspecies hyperborea is characterized by its greatly reduced white maculations (thus, exhibiting expanded dark areas) and overall smaller size, both of which may be regarded as heat conservation adaptations for the far boreal climate in which it lives.

¹ Excluding the federally endangered Cicindela albissima (Coral Pink Sand Dunes tiger beetle), which was recently elevated to species status based on mitochondrial DNA evidence (Morgan et al. 2000).

The fragmented nature of the main limbata population in the upper Great Plains and into the boreal forests is, in itself, interesting enough. Even more interesting, however, are the existence of two small and highly disjunct populations far removed from the main limbata population. One of these is known from Labrador – almost 3,000 miles to the east! Originally referred to subspecies hyperborea, this population was theorized to possibly represent an accidental introduction since individuals appeared to be restricted to open sand habitats within 70 km of the Goose Bay airport (Larson 1986, Pearson et al. 2006). However, careful examination of individuals from this population revealed subspecific differences in maculation (intermediate between hyperborea and nominotypical limbata), lending support to the hypothesis that it is a naturally occurring population and resulting in its description as a distinct subspecies, labradorensis (Johnson 1990). Recent analysis of mitochondrial DNA sequences provided additional support for this subspecies as a distinct entity (Knisley et al. 2008), and newly published field observations by tiger beetle afficionados Dave Brzoska and John Stamatov (2008) conducted 19 years after the initial discovery of the population suggest it is well established in suitable habitats much more distant from Goose Bay than originally reported. This accumulation of evidence seems to increasingly support a historical isolation rather than accidental introduction hypothesis. The fifth and final subspecies is an even more recently discovered and equally disjunct population in the Nogahabara Dunes of northwestern Alaska (Pearson et al. 2006). Although individuals from this population resemble subspecies nympha, morphological and mitochondrial DNA sequence analyses support its status as a distinct subspecies, designated nogahabarensis (Knisley et al. 2008). Such an unusual and fragmented distribution for Cicindela limbata and its subspecies is likely the result of historical changes in climate that have caused expansions and contractions of open sand habitats due to fluctuations in available moisture. The current geographical subspecies may have originated at the end of the mid-Holocene hypsithermal (or Holocene Climatic Optimum) some 5,000 years ago, when previously expansive open sand habitats would have begun shrinking and fragmenting as a result of declining temperatures and increasing moisture regimes.

REFERENCES

Brzoska, D. W. and J. Stamatov. 2008. A trip to Goose Bay, Labrador, Canada. Cicindela 40(3):47-52.

Johnson, W. 1990. A new subspecies of Cicindela limbata Say from Labrador (Coleoptera: Cicindelidae). Le Naturaliste Canadien 116(4) [dated 1989]:261-266.

Larson, D. J. 1986. The tiger beetle, Cicindela limbata hyperborea LeConte, in Goose Bay, Labrador (Coleoptera: Cicindelidae). The Coleopterists Bulletin 40(3):249-250.

Knisley, C. B., M. R. Woodcock and A. Vogler. 2008. A new subspecies of Cicindela limbata (Coleoptera: Cicindelidae) from Alaska and further review of the maritima group by using mitochondrial DNA analysis. Annals of the Entomological Society of America 101(2):277-288.

Morgan, M., C. B. Knisley and A. Vogler. 2000. New taxonomic status of the endangered tiger beetle Cicindela limbata albissima (Coleoptera: Cicindelidae): evidence from mtDNA. Annals of the Entomological Society of America 93(5):1108-1115.

Pearson, D. L., C. B. Knisley and C. J. Kazilek. 2006. A Field Guide to the Tiger Beetles of the United States and Canada. Oxford University Press, New York, 227 pp.