Thursday, August 11, 2011

Margined Blister Beetle

The next guest on our list of garden enemies is the margined blister beetle.
We've had this pest in our flower gardens before.   For years, they regularly ate our clematis virginiana down to sticks.  We finally dug up the clematis and hadn't seen the bug in a couple of years.   Then this year it showed up on some tomatoes and eggplant - eating the leaves to nubs.    The next day I noticed that the potato greens had been devoured.    We found dozens of these bugs in the straw around the plants.   They lay their eggs in the soil, so we have to wait for them to come up to get them. 

Rumor has it that these guys eat grasshopper eggs - which is great, except they will eat a plant to nothing, too.   Big problem. 

An even bigger problem is the fact that their bodies produce a toxin so powerful it will kill a horse and blister human skin.   Some varieties of blister bug are more powerful than others.

Truth told, I squashed dozens of these bare handed before I knew what they were.   No blisters.   I double checked the photo ID and there's no doubt what they are.   Either Eric and I got really lucky, or these just aren't as toxic as some of the others.

Handle with gloves!   But get them off your plants. 

These beetles leave a characteristic poop trail - messy wet black droppings.  That's how you'll notice them.   Look behind the leaves for the bug.  Careful picking off of these guys seems to control them.    Though we picked dozens off the potatoes the first day, there were only a few the second day and I haven't seen any since.  We're fighting them on the tomatoes now - more hiding places.    

Just drop the beetles in a bowl of hot soapy water to kill them.


  1. I don't think we all realized how involved it is to garden without depending on chemicals. Are there any natural concoctions that you use, or is all just pick and squish?

  2. Kitten - You can use a tea made from pyrethrum [painted daisies] and I've heard a tea made with capsaicin [chili pepper oil] works, too on some bugs, but they'll wash off in the rain, so I generally do the pick and squish thing.

    For the vine borer we had to get a BT [Bacillus thuringiensis] powder - nothing works better and it's a naturally occurring bacteria.

  3. I think I used that BT on my houseplants. I'd bought soil from a place that stored it outside. Although it was dry when I bought it, it had apparently been soaked in the rain, which makes it heaven for the gnats. The first time I watered I was inundated. They could barely fly a few inches, but it was enough for them to move to established plants and spread. Since then I've learned to Isolate and Microwave new soil. You might kill some good microbes or whatever, but it's worth it.

  4. These guys just devoured our potato plants in less than 24 hours! Glad I didn't touch em ;)

  5. Robin, your gardening posts are amazingly helpful! Here it is a year (almost) after this post, and today my 6 year old and I went out blister bug hunting! It was great fun, and we'll probably go again to get the ones we didn't catch! Thanks for making my gardening a little easier!

    1. Hi Jessica! I'm glad this post was helpful. I haven't seen any of these guys yet this year, but I'm a firm believer in Constant Vigilance! [The Mad-Eye Moody school of gardening.]

  6. Thank you for your post on these bugs. I found some today and luckily had my gloves on when squishing. I spotted the nasty excrement as well. Your post was the only entry I found explaining these bugs, but i will look further now that I know the name.


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