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Golden tortoise beetle: all that glitters

Bob Dluzen
Special to The Detroit News

A gardening friend of mine was excited to tell me about a discovery she made in her garden this week. She told me she had found a round, shiny gold thing in her flower garden! We drove over to her garden to take a look at it.

It turned out to be a Golden tortoise beetle. It really did look like a molten drop of gold had dripped into her garden. I don’t ever recall seeing one in all the years I have been gardening.

These insects are about the size of a ladybug, maybe a bit smaller. Their name is completely descriptive. They are the rich, golden color of jewelry and like a tortoise, they pull their legs under their shell when bothered.

If that’s not surprising enough, they are able to change their color from gold to brown whenever they want, especially when disturbed. This particular one had no desire to change, it stayed gold despite all our handling.

Color change is done by the beetle varying the amount of water in the outer layer of its shell. As the shell is hydrated, it takes on the golden color. Removing water causes the shell to revert to a browner color. This process only happens as long as the beetle is alive. Once dead, its golden color is lost.

The visual enjoyment golden tortoise beetles provide more than makes up for the small amount of damage they might cause in the garden.

Golden tortoise beetles feed only on plants in the morning glory family. That includes morning glories, sweet potatoes, field bindweed and similar plants. My friend found this one on one of her morning glory vines.

Both the larvae and adults feed on the leaves and flowers making a number of separated holes as they chew. The damage is only cosmetic however. No real harm is done to the plant.

They prefer to spend their time on the underside of the leaves making them somewhat hidden from view. In fact, after we were done looking at it, we set the beetle on the top of a morning glory leaf. It immediately crawled to the edge, gracefully went over the edge and continued as if the leaf edge wasn’t even there.

As it warms up in the spring, the beetles come out and look for food to eat. Lucky for them field bindweed is a perennial that begins growing very early providing the golden tortoise beetles with their first source of food. They often eventually move to gardens as more plants start to grow during the gardening season.

Later in the spring, females lay single eggs on the leaves of the host plant. The larvae begin feeding as soon as they hatch. Once full-sized, they will pupate on a leaf. After a week or two they finally emerge as those shiny, golden adults. They will continue eating for as long as they can through autumn as they prepare  for winter.

The beetles then overwinter under fallen leaves and other garden debris. That makes a case for leaving some debris in the garden and not getting too gung-ho about removing every last leaf. A little mess may bring beauty later.