Blister Beetles (family Meloidae) are small insects that can cause damage to food crops and other flowering plants. The species pictured here, Nemognatha punctulata, is the only species I have seen in my Central FL garden. Here it is on a coreopsis leavenworthii flower, the Florida state wildflower.
Although I do not worry about seeing blister beetles on a wildflower, it is somewhat concerning seeing them so close to my food crops and other flowers. They are known for their damage to flowers but one species, Epicauta, is known for its damage to food crops. In Florida, Epicauta have caused damage to foliage of alfalfa, beets, potatoes, tomatoes, and other crops. The The damage appears on the leaves of the plants. In severe cases, it will appear as if everything but midrib and some veins has been eaten. Below is a picture from the University of Florida's website demonstrating foliage damage caused by blister beetles.
There are several types of blister beetles found in Florida. They vary vastly in color. However, they remain constant in shape with long bodies, wings, and proportionate heads. The adults are usually brightly colored and larvae are typically hard to see. The larvae pose a threat to your garden's pollinators as they have been observed eating young bees, and bee eggs.
When it comes to management of blister beetles in the garden, removal by hand is the most effective. With a gloved hand, simply pick or push beetles off the plant and place into a cup of soapy water. There is not a lot of information on natural predators, however it is believed that birds are the most effective natural control. If damage is becoming severe, spinosad has proven to be an effective chemical treatment.
Exercise caution if removing blister beetles by hand. Their name comes from the vesicant like effect they have on skin. This typically only happens if the beetles are squished on skin, such as when smacking the back of your neck when you feel something crawling on you. The irritant is called cantharidin and has been used in the past in human and veterinary medicine. Today cantharidin is still used in some wart removers.
Although blister beetles are a gardening foe, they can typically be left alone as another member of your garden's ecosystem.
Check out the University of Florida's page which is filled with more detailed information.