Huge brown beetles appearing on grapevines

A couple of days ago, I was working on the grapevines tying up some wayward canes and removing unwanted growth when all of a sudden a huge brown beetle fell from the vines and clung to my bare arm with its scratchy legs.

It startled me for a second until I realized there was nothing to worry about, it wasn’t going to bite or sting. It was a grapevine beetle, Pelidnota punctata. Actually, it was more afraid of me the I was of him. It immediately dropped off my arm and started to burrow into the grass to get away. When I picked it up to snap a photo of it, it kept running away whenever I tried to take a picture.

The beetles only live for about a month in this adult stage of their life cycle. In the beetle stage, they have all of the body parts necessary to reproduce, so their primary objective is to mate and lay eggs.

The adults feed almost exclusively on grapevines, both cultivated and wild. They are nocturnal and spend their time eating and flying to other grapevines to look for mates.

During the day they are not active and just rest and take shelter in the foliage of the grapevines.

Once mating has taken place, the females lay their eggs, one at a time, under decomposing wood such as fallen tree trunks and old stumps. The larvae eat decaying wood so the female always makes sure her young will have something nutritious nearby to eat after they hatch.

They will stay in the larval stage for around two years eating and growing. Once they get to the right size, they form a cocoon and pupate. After only two to three weeks in the cocoon, they emerge as adults in late June or early July. Those are ones were seeing now.

The beetles rarely cause enough damage to grapevines to justify taking control measures. But if you are worried about them taking a bite out of your grape leaves, they are easy enough to pick off by hand and feed to the chickens.

I tend grapevines in two locations about 25 miles apart. One vineyard has grapevine beetles and other doesn’t, even though there are enough wild vines growing nearby to sustain a population. As a matter of fact, the site without the beetles has rotting wood right next to it while the other with beetles has no wood for hundreds of yards away. So while grapevine beetles are common, they do not occur in all locations.

This is another example of all of the wonderful things in nature you can find while gardening.