Friday, May 12, 2006
Six-spotted Tiger Beetle
Name: The six-spotted tiger beetle is Cicindela sexguttata. Guttata is latin for spotted or dappled, and sex — at least in this context — means six. (Many plants and animals have guttata in their name — one of my favorites is the spotted turtle — Clemmys guttata.) There are over 100 species of tiger beetles in the U.S. They are named for the tiger because they are predators.
Wing thing: Most beetles have two sets of wings. The front pair are called elytra (singular is elytron). Elytra are usually hard; they cover the membranous flying wings, and they don't overlap — they meet in a straight line down the center of the abdomen. Typically they cover most or all of the abdomen.
When and where found: I found this beetle in my not-yet-planted veggie garden on April 20. It was a sunny day and the iridescence of the beetle caught my eye. You can often find other species of darker-colored tiger beetles in the sandy soil at Foss Farm. They prefer open dry areas with little or no vegetation, like the sides of the roads and paths at Foss Farm. They are active when the sun is out.
Identifying characteristics: Not all the six-spotted tiger beetles have six spots. Some have more; some have none. The one in my garden was true to its name but the spots, which are on the elytra, are not prominent. In the photo you can just make out one pair of spots about midway down the elytra on the outside edge. There is another pair at the tip of the elytra, and the third pair is even smaller and located halfway between the other two. The most obvious characteristic is the vivid green iridescent color which appears blue at the edges where it catches the light at a different angle. The whole beetle is this color — head, thorax, elytra, and legs. Most other species of tiger beetles have this color only on the lower surface. This specimen was at the low end of the typical size range of a tiger beetle — about half an inch from the head to the tip of the abdomen. The long slender legs had a lot of short white hairs.
Behavior: Tiger beetles are very fast runners and fast flyers. They are also alert and wary and hard to catch. Their speed and alertness help them avoid predators and also help them catch prey which they do both on the ground and in the air. Even though the six-spotted tiger beetle is the slug of the family, it is still quite fast and doesn't pose for the camera. I had to catch this one for its photo op. The female tiger beetle lays her eggs one at a time in the ground just below the surface. When the larvae hatch, they dig a vertical tunnel an inch or two down into the ground and prey on insects passing over the tunnel opening. As the larvae grow, they widen and deepen their tunnels. They keep the tunnel opening level with the ground, unlike ants, wasps and ground-nesting bees which leave the excavated dirt in a heap around the hole.
Food chain: Six-spotted tiger beetle larvae prey on ants, spiders, and other small insects that come within range. The larvae wait at entrance of their tunnels with the flattened area on the back of their heads obscuring the tunnel opening. Adult beetles also like to eat ants but will take a variety of small arthropods. They are known to pounce on their prey and also to kill it by holding it in their jaws and banging it on the ground. I put "my" beetle back into the garden with instructions to focus on pests. Tiger beetles themselves are prey for birds, dragonflies, robber flies, frogs and other small animals. Tiger beetle larvae are consumed by moles, raccoons, skunks, ants, birds and hister beetles, and they may also be attacked by parasitic wasps and mites.
References: Richard E. White, Peterson Field Guide to Beetles; Donald W. Stokes, A Guide to Observing Insect Lives — this book covers few species but is an excellent guide to observable behavior and has practical information on finding insects; www.bugguide.net - this is a great resource with lots of photos and you can submit your own photos with a request for ID.
Turtle hatchlings: Two baby painted turtles, which must have hatched very recently, were crawling around the edges of the horse ring at Foss Farm on May 5. They were heading south in search of water.
Please feel free to write the Biodiversity Corner. The only requirements are that the topic exists in the wild and was seen in Carlisle. Or send photos, sightings, or ideas for the column to Kay Fairweather at 392 School Street, Carlisle MA 01741 or to email@example.com
© 2006 The Carlisle Mosquito