"Cassida rubignosa is the formal name of a beetle. In its larval form, it carries a small sack of garbage around on its back. There's a little pronged fork sticking up at the end of its abdomen. When the larva molts, the old skin catches on the fork and makes a kind of garbage bag. The anal aperture is right there, too, and fecal matter is deposited in the bag. For a long time, zoologists pondered the purpose of this arrangement.
Then they noticed the ant. A hunting ant that likes to eat beetle larvae. An ant that is also fastidious in nature, grooming itself often to keep tidy.
So when the ant scurries up and gives the larva a preliminary feel to size it up for dinner, the larva hits it with the garbage bag. The ant falls back to clean up the noxious mess and the larva slumps away. Zoologists refer to this device as a fecal shield."
- 'All I Really Need To Know I Learned In Kindergarten', Robert Fulghum.