outdoors Scot Stewart

A six-spotted tiger beetle.

Tigers in the sandbox

Story and photos by Scot Stewart

They hunt by day, right under your feet. With bulging eyes and big jaws, they’re ready to chase down and pounce on an unsuspecting ant or other small insect wandering along a sunny dune or open, sandy bank. They are Tiger beetles, one of the most interesting, colorful groups of beetles.

Beetles are the largest group of living things on the planet and belong to the division or order of insects called Coleoptera. So far, more than a quarter million beetles have been named, which is about 1/5 of the 1.2 million living species known named and identified to science so far. And while the numbers change all the time, other numbers (like 8.7 million, using diversity pattern estimates) are widely recognized as a starting point toward the truer number. Still, the number of beetles is impressive, and the diversity of tiger beetles is, too. At least 100 different types are found in the United States, and worldwide. There are more than 2600 different kinds of tiger beetles.

These are small dynamos, most between half and three-quarters of an inch long. Because of their size and their take-flight behavior when startled, they are rarely noticed. They can also run extremely fast. (More about that later.) Most live in the tropics, but more than a dozen species live in Michigan. The best places to look for them are in sand dunes, along sandy trails and in sparsely vegetated dry areas. Around the world, most live on the ground, but in tropical areas some live in trees.

Tiger beetles are incredibly colorful. Some have entirely bright green exoskeletons, while most in the U.S. are brownish with calligraphic markings on their back and amazing hints of metallic green, violet and purple across

their bodies and legs. Some also have lots of hair-like structures across their mid-section, or thorax, and legs. Their markings help camouflage them on the sand and among the dried parts of plants so well that even after watching one land, to look away for a minute means probably losing it in the mix. Some of the tropical species look like they have been splashed with the best metallic paints ever used on race cars, but can still blend in, matching sunspots, flower petals and other bright, colorful dabs of light and life among the ground cover. Tiger beetles are insect eaters. They feed mostly on ants, insect larvae and spiders, but will hunt just about anything small enough to catch. Their eggs are laid in the ground, and the young larvae dig a tunnel up to 2 feet down where they live. These immature beetles hunt by coming to the surface and waiting for prey to wander by.

September 2021 Marquette Monthly 29

An adult oblique-line tiger beetle emerges from its larval burrow. Tiger beetles spend up to four years in the larval stage.

Using an ambush strategy, when a meal gets close enough to them, they jump at it and grab with large, sickle-shaped jaws. They have hooks on the lower part of their body to anchor themselves to the ground so their prey can’t drag them away while struggling. They have similar sets of hook-like features on their backs to help them move up and down the burrow after they catch their prey to eat it. Some tiger beetles have digestive fluids they can use to break down larger prey like spiders before they eat them.

As large-jawed, grub-like larvae can live in these burrows, go long periods without food or water and even survive flooding of their cavities, tiger beetles can spend up to four years in this stage, depending on the species. They are preyed upon by other insects like ground beetles, attacked by ants and dug up by birds. Several species of wasps lay their eggs on the immature beetles and the beetles are parasitized by the larval wasps before dying.

When the larvae finally mature, they close off the opening to their burrow, and pupate, going through their metamorphosis into adults. After about three weeks, they emerge from their pupal case, still in the earth, and remain there for up to three days as their exoskeleton hardens. When complete, they dig their way out and begin a short four-to-eight-week life as an adult.

While tiger beetles are mostly solitary, they can live close together in good hunting areas. In the path leading to Lake Superior near the mouth of the Dead River, half a dozen oblique-lined tiger beetles can be found at a time in late summer.

The path from the Little Beaver Campground at Pictured Rocks National Lakeshore to Lake Superior passes a sandy rise just before reaching the lake where a similar group lives during the summer months.

Even small spits of sand can attract tiger beetles. There is a small V-shaped point jutting out on the north side of Harlow Creek where bronzed tiger beetles lie in wait for flies and other small insects to stop and sun themselves on cool mornings.

A subspecies of the hairy-necked tiger beetle, the Rhode Island hairy-necked tiger beetle, Cicindela hirticollis ssp. Rhodensis, was found on the Lake Superior beach in Grand Marais earlier this summer. As its name suggests, this variety is more commonly found in New England, but by the 1960s it had made it across the Great Lakes to Duluth. It was found in Alger County, right in the middle of a beach heavily used by bathers.

It is almost impossible to find a tiger

TIGER BEETLES ARE SIMPLY A GREAT EXAMPLE OF NATURE DESIGNING AN AMAZING SET OF CREATURES ... WONDERS OF ADAPTION, DESIGN AND BEAUTY.

A bronzed tiger beetle is pictured. There are hundreds of types of tiger beetles found in the world. Several different species can be found in Michigan. Keep an eye out on the beach for a glimpse of these elusive, amazing creatures.

beetle by just scanning the ground — even in an area where tiger beetles are known to be: they just blend in too well. If a tiger beetle does happen to dash across an opening on the sand, it might be noticed. Often, they become apparent to a trained eye when they fly up in front of a disturbance, like someone walking down a path or along the edge of some dunes. It takes a little patience to follow the flight and see where they land.

Then it takes even more patience to slowly ease toward them. That is easier early in a cool morning when they are still sluggish and trying to warm and get their metabolism to speed. Easing toward them on hands and knees, maintaining a low profile works best, sometimes allowing close-up looks at their tremendous jaws, bulging eyes and gorgeous colors. Usually, the look does not last long, and they are off in search of prey. But that close-up look is impressive. They won’t bite, unless handled, and then it is just a gentle squeeze as the jaws are meant to hold, not crush.

When they do rush off to hunt, their speed is blinding, literally out of sight. Tiger beetles, like most insects, have compound eyes. Each eye is a composite of many smaller parts called ommatidia, structures that each contain a lens and opsins, parts used for observing color. The number of ommatidia in each eye limits the amount of light each eye can take in and the total set assembles a collective picture of what the insect is viewing.

Unfortunately for tiger beetles, the number of ommatidia is not enough to give them a good picture of prey they are chasing or anything in front of them when they are running or flying fast. For careful viewers, it is possible to actually see them fly into stalks of plants as they attempt to escape danger. They are going too fast for their compound eyes to keep up.

For hunting it is even worse. They are among the fastest runners of all animals. They only run short bursts, many up to 1.2 mph but one species can sprint at speeds up to 7 km or 5 mph. Maybe that does not seem very fast, as world class human sprinters can run 23-plus mph. So, it is necessary to look at it a different way. That human sprinter can cover five body lengths of distance in a second. Tiger beetles going 1.2 mph can cover nearly 54 of its own body lengths per second — in relative terms, 10 times as fast.

That is where the problems begin. Like the flying tiger beetle, running down a meal turns into a blur for them — they can no longer see what they are chasing. They must stop, up to four times, during a chase to relocate their prey before catching it. Fortunately, they are so much faster than most other insects, they can still catch them.

Their speed is due to their long legs. They provide greater strides and more speed and help them clear larger grains of sand, grass blades and other potential obstructions during the chase.

Tiger beetles are simply a great example of Nature designing an amazing set of creatures, though not clearly known to many, still wonders of adaptation, design and beauty. To get a full appreciation of them truly requires getting down on hands and knees, being patient, and becoming a true student of their entire biological community. Several national park visitor centers and nature centers have celebrated their design and colors with large-scale paintings and tapestries to encourage visitors to take that extra moment to bend down and take a look at a true wonder.

About the author: Scot Stewart has lived in Marquette long enough to be considered a true Yooper even though he was born in Illinois. He is a teacher and loves to be outdoors photographing and enjoying nature.