Beetles of the Dunes

By DIRK J. STEVENSON

Georgia’s river dunes are extremely deep sand ridges that occur on the northeast sides of major streams in the Coastal Plain. These ridges, formed 15,000-30,000 years ago, are composed of droughty, coarse and excessively well-drained sands from 10-30 feet deep.

Called aeolian dunes or riverine dune sandhills, they were formed by westerly winds transporting sands from exposed river bars onto the east and northeast banks of sizeable drainages.

Early naturalists called these habitats “deserts in the rain.” Despite high annual rainfall, the soil has little water-holding capacity and most rainwater is lost via rapid percolation. The sand is acidic and nutrient-poor: It’s a tough place for flora and fauna to make a living. There are many odd specialists, plant and animal, and unsurprisingly a number of the animal endemics live underground for much of their lives.

This year, the DNR Wildlife Conservation Section supported field surveys for rare and poorly known insects – identified as species of greatest conservation need in the 2025 State Wildlife Action Plan – at Alligator Creek and Ohoopee Dunes wildlife management areas, among other sites. As part of this effort, coleopterist Roy Morris and I targeted a number of beetles endemic to aeolian dune sandhills.

Several new sites and noteworthy records were discovered for a diminutive scarab beetle, Geopsammodius ohoopee. These blind, flightless and only 3 millimeter-long beetles are fossorial, denizens of loose sand. To locate them, Morris and I passed sand through the fine mesh screening of a sifter, like archaeologists searching for fragments of artifacts.

These surveys produced sensational, and unexpected, “by-catch” when another insect that prefers sandy soils, a hister beetle called Spilodiscus skelleyi, was collected. This was the first record for this species outside of Florida.

This unusual hister beetle is named for beetle biologist Paul Skelley, who, coincidentally, discovered Geopsammodius ohoopee. Members of Spilodiscus are often specialized inquilines, that is, creatures dependent on the burrows of specific vertebrates. However, any burrow dependency in the life history of S. skelleyi has yet to be determined. Meanwhile, two hister beetle species that are obligate commensals of gopher tortoise burrows were documented at both Alligator Creek and Ohoopee Dunes WMAs.

Not just unusual beetles, but strange plants dominate sandhills. Characteristic flora sure to catch your eye include aromatic woody mints (Clinopodium spp.), the singular rosemary (Ceratiola ericoides) and a late-summer blooming aster with lime green leaves and yellow flowers known as woody goldenrod (Chrysoma pauciflosculosa). The significance of woody goldenrod to insects cannot be overstated. At least two beetle species and three moths have life histories intimately tied to this plant.

Morris first discovered the Ohoopee Dunes Crossidius beetle (Crossidius grahami) in the late 1990s and formally described it as a new species with James Wappes in 2013 (Morris named it for his son Graham). The beetle is known only from dunes along the east side of the Ohoopee River and is notably disjunct from its closest relatives – other beetles in this genus are western, occurring from California to Texas and into Mexico.

A type of longhorned beetle, larvae of the Ohoopee Dunes Crossidius beetle have rigid habitat requirements. Wood-feeders, they develop only in the root crowns of woody goldenrod. Interestingly, another cerambycid endemic to Ohoopee Dunes, this one named for Morris (Plesioclytus morrisi), occurs in the very same areas. Its larvae are also highly specialized, feeding on the root crowns of October flower (Polygonella polygama).

Two new populations of the Ohoopee Crossidius beetle were discovered this year. Several larvae were collected by whittling into infected root crowns, then carefully extracting the larvae from galleries they had bored into the wood. They were sent to Dr. Patrick S. Gorring, a cerambycid expert and research curator at the Florida State Collection of Arthropods. Gorring is sequencing DNA from beetle larvae to assign them to species. His goal is to complete a description of all larval longhorn beetle genera in the U.S. and produce a key for their identification.

Summer rains and high levels of humidity also brought handsome earth-boring scarab beetles (Bradycinetulus ferrugineus) to the surface and a number were captured at Alligator Creek during their night-flights in June and July. A sandhill species, they dig burrows that could make a gopher tortoise jealous. A running joke among entomologists is, “Bring your posthole digger if you want to see Bradycinetulus, and expect to be there awhile.”

The deepest burrow recorded reached 11 feet deep, although most are closer to 2-4 feet.

Two new populations of the uncommon autumn tiger beetle (Cicindela nigrior) were also documented. This tiger beetle is unusual in being active only during late summer and autumn. The species lacks markings and is polymorphic: Adults may be black, green or violet.

Remember, beetles are the most diverse group of animals on Earth, and entomologists have yet to find and describe many of them. Elytra-clad treasures that are new to science and call Georgia’s river dunes home may await discovery.

EXPLORING SANDHILLS

DNR has protected many outstanding examples of aeolian dune sandhills, which, now flush with the colors of late-summer wildflowers such as blazing stars, summer farewell, asters and mints, are fine sites for a relaxing October hike. Some recommended places to explore:

• In the Canoochee River drainage: George L. Smith State Park (Emanuel County), Canoochee Sandhills WMA (Bryan/Bulloch counties).
• Little Ocmulgee River drainage: Little Ocmulgee State Park and Lodge (near McRae-Helena), Alligator Creek WMA (Wheeler County).
• Ohoopee/Altamaha River drainage: Ohoopee Dunes WMA (Emanuel County); Big Hammock WMA (Tattnall County) (also see: “A botanical treasure“), Griffin Ridge WMA (Long County), Townsend WMA (Long/McIntosh counties).

Learn more about WMAs at georgiawildlife.com, including details on hunting seasons under way. WMA access requires a hunting or fishing license or a lands pass. All are available at gooutdoorsgeorgia.com.

Dirk J. Stevenson is a zoologist and owner of Altamaha Environmental Consulting.

Top: In sandy soils, burrows of the inch-long earth-boring scarab beetle can be 11 feet deep. (Dirk J. Stevenson)