Cicindela scutellaris (festive tiger beetle) is widely distributed in the U.S., having been recorded from most areas east of the Rocky Mountains except Appalachia, the lower Mississippi River delta, and south Florida. Within this range, the species occupies deep, dry sand habitats without standing water. It is often found in the company of Cicindela formosa (big sand tiger beetle), whose range largely coincides with that of C. scutellaris (except the southeastern Coastal Plain). More than any other North American Cicindela, populations of this species show extraordinary variability in color across its range of distribution. Seven geographically recognizable subspecies are generally accepted, with considerable variation evident within some of these and along zones of contact between them.
The greatest portion of the species’ range is occupied by nominotypical populations in the Great Plains and subspecies lecontei in the Midwest and northeast. Similar to what I’ve noted in previous posts for other species, a broad zone of intergradation between these two subspecies occurs along the upper Missouri River. Other subspecies occupy more limited ranges along the upper Atlantic Coast (rugifrons), southeastern Coastal Plain (unicolor), eastern Texas and adjacent areas of northwestern Louisiana and southwestern Arkansas (rugata), and north-central Texas (flavoviridis), and the highly restricted and disjunct yampae is found only in a small area of northwestern Colorado. Populations in the upper Midwest and Canadian prairie are sometimes regarded as distinct from lecontei (designated as subspecies criddlei) due to their broadly coalesced marginal elyral maculations, and an apparently disjunct population of small, blue individuals in south Texas may also be regarded as subspecifically distinct.
Although Missouri lies well within the boundaries of its range, this species has been found in only three widely-separated parts of the state – near the Missouri River in the northwest part of the state, near the Mississippi River in the extreme northeast corner, and in the southeastern lowlands (formally known as the Mississippi River Alluvial Basin). The two northern Missouri populations are assignable to and typical of lecontei, with their uniform dull maroon to olive green coloration and continuous to near-continuous ivory-colored border around the outer edge of the elytra. Additional dry sand habitats occur along the lower Missouri River in central and east-central Missouri and along some of the larger rivers that drain the Ozark Highlands; however, this species has not been located in these habitats despite their apparent suitability and occurrence of C. formosa with which it frequently co-occurs. The reasons for this distributional gap between the northern and southern populations – some 400 miles in width – remain a mystery. The southeastern Missouri population is not clearly assignable to any subspecies, apparently representing an intergrade between lecontei to the north and unicolor to the south. Accordingly, individuals from this area are known by the unwieldy appellative “Cicindela scutellaris lecontei x scutellaris unicolor intergrade.” Pearson et al. (2005) states that intergrades between lecontei and unicolor are evident only in northern “Missouri” (an obvious error for Mississippi) and Tennessee. Thus, the existence of intergrades in southeastern Missouri suggests that the zone of intergradation extends further north than previously realized.
Prior to this season, I had located two main population centers in the southeastern lowlands – one at Holly Ridge Conservation Area in Stoddard County, and another at Sand Pond Conservation Area in Ripley County. Holly Ridge is located on Crowley’s Ridge – an erosional remnant of Tertiary sand and aggregate sediments left behind by the late Pleistocene glacial meltwaters whose scouring action formed the surrounding lowlands, while the sandy sediments at Sand Pond were deposited west of Crowley’s Ridge along the southeastern escarpment of the Ozark Highlands during that same period. These erosional and depositional events created the deep, dry sand habitats that Cicindela scutellaris requires. I had known also about the Sikeston Sand Ridge further to the east – another erosional remnant of Tertiary sands deposited by the ancient Ohio River – but had not explored it closely until this season when I initiated my surveys at Sand Prairie Conservation Area. I expected Cicindela scutellaris might occur here, and in my first fall visit in early September I found two individuals in the sand barrens (alongside Cicindela formosa). Another individual was seen here in early October, but more robust populations were observed at a small, high-quality sand prairie remnant (last photo) further to the south along the Sikeston Ridge, and around eroded sand barrens behind private residences still further to the south. Clearly, the species is well-established in the southeastern lowlands wherever open dry sand habitats can be found.
The individuals shown here exemplify the range of variation exhibited by Cicindela scutellaris populations in southeast Missouri. They greatly resemble subspecies unicolor by their uniform shiny blue-green coloration. Indeed, the individual in the first photo might well be classified as such due to the complete absence of white maculations along the elytral border. Most individuals, however, show varying development of such maculations, ranging from small disconneted spots to the more developed apical “C”-shaped mark – clearly an influence from subspecies lecontei. Another apparent lecontei influence is the suffusion of wine-red or maroon coloration that can be seen on the head, pronotum, and elytra of the individuals in photos 2 and 4. These characters make this population divergent from the typically monochromic unicolor (as its name suggests). Because of their bright green coloration and white maculations, individuals in this population greatly resemble subspecies rugifrons, but that subspecies is limited to the northern Atlantic seaboard. They also resemble the common and widespread Cicindela sexguttata (six-spotted tiger beetle) but can be distinguished from that species by the more noticeably domed profile of the elytra, rounded rather than tapered elytral apex, and dark labrum of the female (both sexes of C. sexguttata have a white labrum).
There is one additional sand ridge in Missouri’s southeastern lowlands – the Malden Ridge. This sand ridge occurs south of Crowley’s Ridge and is much smaller than the Sikeston Ridge. No significant remnant habitats remain on the Malden Ridge, but it is possible that sufficient areas of open sand remain that might support populations of C. scutellaris. Determining whether this is true will require some time studying Google Earth and even more time on the ground to search them out. If they do exist, however, it will be interesting to see what level of influence by lecontei is exhibited in this most southerly of Missouri populations. Only spring will tell!