This beetle is a Black and red lined blister beetle and the ‘sack’ is just part of the abdomen of this beetle. By the size of the abdomen this is a female. The males are smaller in overall size and the abdomen in not as large or swollen looking. They do not fly or run. The bright red color tells insect predators to stay away. If that does not work, should the predator get very close the blister beetle will “bleed” from its joins cantharidin, a toxic smelly substance. They are very strange looking! Gorgeous color!
There are 3 species in genus Megetra. These beetles range the southwest U.S. and Mexico, and are often found in the Chihuahuan desert.
Blister beetles produce cantharidin, a highly toxic chemical that irritates the skin (blisters form..hench the common name) and stomach of humans as well as farm animals. It could lead to death if ingested, especially in horses. Therefore it is a concern for hay producers should the beetles get caught in the hay and inadvertently eaten by livestock.
These beetles feed on various plants, but are not considered a pest, except for the blisters 🙂