Sometimes I’d rather not meet cousins, particularly when it comes to garden pests. This morning while turning on the water on my kale and keyhole garden, I noticed gray beetles over my kale and the floating row cover. They looked familiar, but the spots threw me. After a bit of research through Montana State University Extension, I determined it’s the dark spotted blister beetle. Oh, joy. It seems that every few years, they want to visit. 

Identifying the spotted blister beetle

I’ve had issues with blister beetles before but they were a solid black and shiny type, which was probably Epicauta pennsylvanica. I typically dispatched them by sucking them up with the Shop Vac. These gray ones with spots threw me at first so I dug a little more into their lifestyle to figure out if there’s something I can do to avoid them in the future.

One thing I discovered is blister beetles are also called meloid beetles because they produce a toxin called cantharidin. According to the MSU Extension MontGuide on Blister Beetles of Montana, when they’re disturbed, this substance mixes with their blood and is excreted from the joints in their legs. Ew. The fluid actually causes our skin to blister like chicken pox if we come in contact with it. This is why a vacuum is so handy. I don’t want to touch them.

The Life and Diet of a Blister Beetle

They’re primarily issues with commercial crops such as alfalfa, sanfoin, oats, beets and peas. There is one species, Epicauta sericans, that even feeds upon bindweed. Why can’t I have that one some years? I would be happy to see blister beetles if it meant less bindweed.

Plague of Grasshoppers and Blister Beetles

As part of their lifecycle, the adult beetle female lays up to 100 eggs in the soil and after they hatch, they feed upon grasshopper egg pods. Talk about conflict! After two years of terrible grasshopper populations, I’m a fan of anything that knocks them back a notch. Yet, blister beetles decimate crops so quickly. The larvae overwinter in the ground, then are back out as adults between May and July. Now they are chomping on my kale and laying eggs. 

Management of Blister Beetles

In large numbers, blister beetles are problematic in the vegetable garden, but they are serious issue in hay fields. If they are present when alfalfa is cut and are wrapped up with the hay, the toxin they produce can kill a horse. This is why no nonsense pesticides like Sevin are used in this type of situation.

For the home garden, the vacuum works fine, or use a permethrin based pesticide. Spinosad also works well. This is the naturally occurring bacterium discovered in the soil of a closed rum distillery decades ago that affects the digestive track of insects. If blister beetles are a frequent occurrence, dust the plants with diatomaceous earth beginning in the early to mid-summer to discourage them from sticking around.

It’s also my hope that by eliminating the blister beetles now, they’ll not lay eggs. I’ll also turn under the soil to disturb those that might already be there. Blister beetles typically are not a problem every year for some reason. But when they do decide to make an appearance, it’s always noteworthy.