Blister beetles are very similar in shape and color to Lightning Bugs/Fireflies. However, blister beetles do crop damage and they do it quite well when they gather in great numbers. They tend to stay in weedy areas where there is an abundance of grasshopper eggs since the larval stages love this delicacy. The adults damage the crops, but usually they don't gather in great enough numbers to notice the damage.
Adults are slender oblong beetles with yellow stripes in some form. Larva are usually found in several stages and all stages have 3 upper body legs. The pupa stage is a stage of darkening, starting with the eyes. Eggs are oblong and yellow.
They chew on just about any vegetable especially vine and root crops. They are mostly foliage feeders but will eat flowers as well. Not only do they eat your plants, but they leave behind black stringy substances.
Unfortunately, by the time you notice a problem, the crop is pretty much on it's last leg. Treatment after the fact will kill the insects, but it's hard to save the crops once they have been completely defoliated. A preventive measure may be to use rotenone or other organic powders and sprays before you have a problem. This way you can insure that you don't get a problem. Horticultural oils will kill the eggs, but remember these methods also kill beneficials.
The beetles get their name from their tendency to carry a substance called cantharidin. This substance can kill anything by damaging internal and external tissue. Even dead insects can still cause the blisters. The most damage comes from hay that has been treated for blister beetle populations where the beetles are bailed in the hay without knowledge and the animals that eat the hay start to die off. The will affect humans if you pick them up so be careful not to touch.
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