These pretty beetles are mostly bad news. To begin with, they can produce a fluid called cantharadin that, when it comes in contact with skin, justifies the blister part of their common name. Secondly, cantharadin can be very toxic to some vertebrate species, especially horses. There are approximately 100 species of blister beetles in Texas. The adults feed on many types of plants but especially prefer legumes (like alfalfa which is sold for horse and livestock feed). The larvae are considered to be beneficial because they destroy grasshopper eggs or are parasitoids of other insect species. However, larvae of many blister beetle species are pests of solitary bee nests. So the take home lesson on blister beetles is look but don't touch. Or if you must touch them to remove them from your garden plants, then at least wear gloves and throw them away when you are finished. The University of Kentucky has published some information on the number of blister beetles that pose a mortality threat to horses - and this is mortality, not sublethal effects, which can be very bad in themselves. The fact sheet also contains tips for alfalfa growers who want to minimize blister beetles in their hay and it also has tips for horse owners.