Pests and diseases 71
lo and behold, favor Japanese anemones and clematis as well as asters and
dianthus. I also discovered that the larvae are in fact beneficial: they eat grass-
hopper eggs in the soil—amazing! So the dilemma was whether to attempt a
major control effort of the beetles, or to use them as a natural defense against the
grasshoppers and let them eat my anemones and clematis, which were the only
plants they had harmed? Obviously the black blister beetles were there for a
reason, and it felt wrong to me to mess with the intended natural balance. I did
knock off as many as I could, with a booted foot, and smashed them. Do not
handle the adults with your bare hands; the blister beetles get their name from a
nasty chemical they spray, called cantharidin, which causes severe skin inflam-
mation and blisters. You can also use chemical-resistant gloves to knock the
beetles off into a bucket containing a solution of soap and water.
Interestingly, Clematis recta plants that had been cut to the ground earlier in
July (to control their sprawling habit), before the appearance of the beetles,
missed the damage of the beetles’ attack. From now on I will prune clematis to
the ground before the beetles attack. Any beetles that remain when the new
growth emerges are easily knocked off and smashed. In fact, the pruned plants
went on to bloom again sporadically in September.
For the anemone, you should prune to the ground the bare, brown, leafless
stems that remain after the beetles have eaten all the leaves. New growth will
emerge nicely, though my plants failed to flower. In future years, if the blister
beetle numbers increase and spread to other species of perennials, I may need to
resort to different tactics. But for now I want to see if the black blister beetles
have any noticeable effect on my grasshopper population.
Black blister beetle damage on
Clematis recta.