Answer: It's only a guess, but based upon your description and the way they were feeding, I'd say you had a large population of blister beetles visiting your garden. Adults feed on foliage, fruit and flowers, sometimes flying in and invading a garden en mass. Handpick, but wear gloves; the beetles secrete a caustic fluid that can rais blisters on the skin. The organic insecticide sabadilla is effective against them, but they seem to come and go at will. If the beetles are gone, don't bother to spray. Next time you see a beetle or two, handpick and destroy them.
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