The adults feed on foliage, while immature forms are often beneficial because they feed on grasshopper eggs. Blister beetles are important in alfalfa production, not so much for their feeding but because they contain cantharidin, a secretion that is toxic to horses consuming hay in which dead beetles are found. Cantharidin is secreted from leg and body joints of the insect and is toxic even in dried pulverized bodies of dead beetles within bales of hay.
Blister beetles are gregarious and often congregate in large swarms within alfalfa fields.
These swarms move frequently and are typically comprised of one or two species of small striped beetles. Dead beetles may be found in baled hay because crimpers on harvest equipment crush congregating adults. No one has quantified the value of decreased digestibility of ruminant animals that consume one or 30 beetles. Published research results have estimated the number of beetles required for a lethal dose of cantharidin to horses. A summary of some of this information is provided in Table 9.