Bombardier Beetle
The bombardier beetle has adopted a genuinely disgusting yet effective method to ward off its enemies. The insect species lets out a hot, noxious spray of toxic bodily fluids from its anus. The two chemicals are kept separately in the glands, with one holding the chemicals hydrogen peroxide and hydroquinones and others containing the enzymes mix that catalyze the reaction.
When the beetle squeezes its reservoirs, the chemical reaction shootout at almost a boiling point. It creates a warning to its predator to back away quickly if it knows what is good for it.