The insects are blister beetles.  There is only one generation a year, and though they feed on many vegetable crops, their favorite is potatoes. Still, their numbers are rarely high enough for you to notice damage.  Some years their populations soar. In that case, wear gloves or use a hand broom to protect skin and knock them into a container of soapy water. Pyrethrum or neem may be applied to damaging populations. 
Here is more general information: http://extension.umd.edu/hgic/blister-beetle-flowers

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