Nature Notes
by Bob Thomas

One of my former students, Leanne Sarco, is a naturalist at Grand Isle State Park. She recently sent me a photo, inquiring what made the strange tracks. Such questions are fun, but this one sent me scurrying to find an answer. Many conversations with fellow naturalists ran the gamut from tiger beetles to polychaete worms. At long last the answer was given by Dr. Don Harper, retired professor at Texas A&M, through Dr. André Landry: the surface tunnels are made by rove beetles, members of one of the two largest families of beetles, the Staphylinidae. As they push through the sand near the surface, the sand above them is elevated, similar to the tunnels of moles and mole crickets.

Rove beetles are relatively easy to identify. Their paired elytra (the keritanized forewings of beetles that cover the wings when the beetle is not flying; before flight, elytra lift up and allow the rear wings to open for use) are about as long as they are wide. When threatened, rove beetles may curl their abdomen up, leading bugophobes to think they are scorpions. Since many species of rove beetles live where scorpions do not, this behavior probably developed to 1) distract a potential predator to the abdomen away from the more vulnerable head and/or 2) make the rove beetle look bigger than it is.

The yet-to-be-identified species that Leanne asked about typically lives in the intertidal zone (the area above low tide and below high tide) on beaches. Female rove beetles make and maintain vertical burrows in the sand with lateral tunnels in which they lay their eggs. In a somewhat rare demonstration of parental care in the insect world, the females maintain the integrity of the tunnels until their young are able to leave and establish their own burrows. When the surf washes over the home burrows, the air inside prevents salt water from entering and drowning the beetles.

Leanne collected a couple of larval specimens by scooping the sand under the tunnels with a tea strainer. She found them in still moist sand near the high tide swash lines (about 10 meters from the surf that day).

The moral of this story is to keep a keen eye out for strange patterns in nature. They usually reveal a novel lifestyle of an interesting critter.

Horizontal tunnels of a species of marine                                           A typical rove beetle. Note the elytra
rove beetle (Staphylinidae) in the intertidal                                       (rusty colored wing covers) that, as a pair,
zone of the beach at Grand Isle                                                        are about as long as wide.
State Park, Louisiana.                                                                      Photo by afpmb.org.
Photo by Nhu Nguyen.

Typical defensive posture of a rove beetle.                                       Domain of a species of rove beetle that
Some say this mimics a scorpion. It probably                                   inhabits the intertidal zone along the Gulf
just draws attention of a predator away from                                   of Mexico. This is a very effective method
the more vulnerable head of the insect.                                           of allowing the insect to live in a salty
Photo by nationalinsectweek.co.uk.                                           environment while minimizing direct
                                                                                                    contact with sea water.
                                                                                                    Photo by cgi.unk.edu.

A tiny larval rove beetle (near the top left
of the dime), collected from a burrow like
that shown in the illustration above.
Photo by Leanne Sarco.