By RICK BORCHELT
It’s spring, and tigers are on the hunt in Maryland. Very tiny tigers.
Tiger beetles.
What they lack in size, these pint-sized predators more than make up for in sheer killing power. Even as larvae, these beetles have oversized jaws and lightning-fast reflexes that make them unmatched hunters for their size, in the insect world. They come by their moniker “tiger” beetle honestly.
Maryland has nearly 30 species of these charismatic beetles, occurring in every county in the state. They live in a variety of habitats — forest trails, mud flats, baseball diamonds, lake margins — even hot sandy beaches in the swelter of midsummer.
Most tiger beetles share some distinguishing characteristics. They typically have long, thin legs designed for running after prey — entomologists call this a cursorial leg. Their long legs provide another advantage, especially for species that run across hot surfaces: They lift the body up off superheated beach sand, shale barrens and the like.
Tiger beetles also use those cursorial legs for a behavior called stilting — raising their bodies off the ground or angling themselves in relation to the sun’s rays. They stilt either to keep cool or, when the weather is chilly or cloudy, to find the right basking posture to absorb the sun’s warmth. In this way, tiger beetles usually maintain a body temperature of around 104 F — no mean feat for a cold-blooded insect in early spring.
Cursorial legs have given tiger beetles the undisputed title of fastest running insect on Earth. Top prize among them goes to a tiger beetle in Australia that can travel as fast as 8 feet per second, or more than 200 miles an hour.
Predation starts early in the tiger beetle clan. The female finds a spot with deep soil — preferably clay or packed loam — and lays an egg in a shallow hole she constructs. When the egg hatches, the worm-like grub digs a tunnel, usually about a foot deep, where it lays in wait for passing prey like ants or other insects. The grub plugs the tops of the tunnels with its flat head, leaving only its eyes and jaws protruding, to ambush unlucky victims. Tactics like this don’t provide a lot of food, apparently; most tigers take two years or more to metamorphose into adult beetles.
Courtesy of M. J. Raupp
In addition to flat, trapdoor heads, tiger beetle larvae have another adaptation to life as a tunnel terror. About two-thirds of the way down their back, they have a pronounced hump with heavy-duty grappling hooks built into it. That way, if they catch prey that puts up a fight, tigers can just dig in and hold on tight to prevent being pulled out of their holes.
Courtesy of Ted C. MacRae
Adult tiger beetles are daytime hunters with excellent eyesight. This visual acuity comes from their large, bulbous eyes made up of hundreds of facets that give the beetle an almost 360-degree field of vision. As anyone who has ever tried to catch one of these agile insects can tell you, they’re much easier to observe than capture.
Here in Maryland, the most prevalent species is the six-spotted tiger beetle (Cicindela sexguttata); they’re easiest to spot in April and May. While only about an inch long, they stand out by dint of their bright metallic green color and penchant for hunting in plain sight on forest paths or trails. The green is relieved only by a few white spots on the wings — usually six, as the name implies — though some populations are spotless. Six-spotted tigers are common throughout Maryland, including in the D.C. suburbs, as long as there’s a shady wooded area. Females lay their eggs at the side of a trail or path.
Courtesy of M. J. Raupp
Maryland also has two federally protected tiger beetles, both of which occur along narrow beaches of Chesapeake Bay. The Puritan tiger beetle (Ellipsoptera puritana) prefers steep, eroding clay bluffs like those at Calvert Cliffs — the same ones that produce prodigious amounts of shark teeth. Females lay their eggs up on the cliff face and the larvae burrow horizontally into the clay. Adults patrol the strip of beach below.
Courtesy of U.S. Fish and Wildlife Service
The Eastern beach tiger beetle (Habroscelimorpha dorsalis) favors the same narrow beaches along the bay, just minus the bluffs. Their eggs are laid on the upper beach and the tunnel is the traditional vertical one. Eastern beach tiger beetle grubs can even survive a day or two being inundated at high tide or during ocean storms.
Sea level rise and bayside development threaten both species, of course, and several of the few Maryland populations have already winked out of existence. Even some once-common tiger beetle species are declining from habitat loss, and from compaction of the soil in heavily used recreational areas. The compaction — from hiking, cars, bicycles — makes the ground too hard for the beetle grubs to burrow in.
If you do manage to sneak up on and capture a tiny tiger, be sure to handle it carefully. Those large jaws can deliver a serious pinch to an unwary tiger tamer.
To see a video of a six-spotted tiger beetle hunting and subduing prey, go to tinyurl.com/2yzznwyh.
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Rick Borchelt is a local naturalist and science writer who writes and teaches about natural history, gardening and the environment. Reach him with questions about this column at rborchelt@gmail.com.
