St. Anthony Sand Dune Tiger Beetle

Sand Dune Tiger Beetle Tunnel

“If the land mechanism as a whole is good then every part is good, whether we understand it or not . . . To keep every cog and wheel is the first precaution of intelligent tinkering.” Aldo Leopold, Round River


Cicindela arenicola is so specialized, it is restricted to just two known locations—the St. Anthony Dune system of southeastern Idaho and the Centennial Sandhills of southwestern Montana. Unfortunately, that makes the beetle exceptionally vulnerable to being lost forever from both natural and manmade threats—drought, invasive plants, trampling by cattle, and off-road recreational vehicles.

Adult beetles burrow into the sand every evening at sunset and emerge the following morning when the sun warms the soil surface. Tiger beetle burrows are flatter than most other digging insects and angle almost horizontally back into the sand before taking a dive a few inches back. Wind quickly obliterates evidence of the burrow entrance and pile of diggings, so when these are present and fresh-looking the beetles have either just dug in or just dug out.

Dunes tiger beetles over-winter as pupae or as adults beneath the surface of the sand. Adults generally emerge from mid-March through April and May, although sometimes as early February. Adults may then disperse from their points of emergence up to one-half mile in six weeks, although most remain in the local area of the dune on which they developed. Adult beetles eat, mate, and the females subsequently lay eggs singly and in random fashion during late April and early May. Adult beetles die during June and few remain at mid-summer.

These eggs hatch in a week or two. Larvae live in stationary burrows located where eggs were laid by adults. Such burrows generally are found in the flat, grassy areas on the windward side of dunes and where the sand is at least three feet thick. Mortality of newly hatched larvae is very high, because few obtain prey during the first five to seven days after hatching, and their burrows are very shallow (0.25-1.0 inch deep), rendering them vulnerable to disturbance. As the larvae become older, they experience less mortality because their burrows are much deeper, reaching up to 18-24 inches in depth. It takes a long time for the beetle to reach adulthood. If food is plentiful, adults may emerge from pupae after two years, but if food is scarce, it may require up to four years.

Both the larvae and adults of the tiger beetle feed on insects and other arthropods.

 

Text borrowed from a Bureau of Land Management report on the St. Anthony Tiger Beetle and Beetles In The Bush, a blog by Ted C. MacRae. Photos by Ted C. MacRae.