Reed warblers have set up a "neighborhood watch" to protect their nests from invasive cuckoos, who lay their eggs in local nests for others to raise. When reed warblers spot a cuckoo, they mob it and emit alarm calls that alert neighbors a cuckoo is at large and they should monitor their eggs closely. This has greatly benefited warblers, but cuckoo populations appear to be suffering.
Along with visual camouflage, Puff adders have evolved a scent camouflage that makes them virtually undetectable to predators. Researchers say these African vipers are the first terrestrial vertebrates known to possess the ability to camouflage their scent.
When yellow jackets sense an intruder, they emit chemical signals known as alarm pheromones that rouse colony members into defense mode and mark intrduders for attack.
Captured damselfish release a chemical distress call that confuses their attackers by calling other predators to the area. The ensuing competition buys them enough time to flee.
When you think of beetles, you probably think of the many harmless bugs that wing around a garden looking for some tasty aphids to devour. They don't bother you, and you likely have no reason to bother them. This changes in the case of the bombardier beetle - a species infamous for its ability to spray a powerful jet of superheated chemicals that can even scald human skin.