In 1938, the Austrian ethologist Karl von Frisch made his first report on the existence of the chemical alarm signal known as Schreckstoff in minnows. An alarm signal is a response produced by an individual, the “sender,” reacting to a hazard that warns other animals, the receivers, that there is danger (Smith 1992). This chemical alarm signal is only released when the sender incurs mechanical damage, such as when it has been caught by a predator. When this signal reaches the receivers, they perceive a greater predation risk and exhibit an antipredator response. Although the benefits to the receivers seem straightforward, it is difficult to determine the fitness benefit to the sender which is required for the maintenance of this trait via natural selection. While the evolution of this signal was once a topic of great debate, recent evidence suggests that scheckstoff evolved as a defense against environmental stressors such as pathogens, parasites and UVB radiation and that it was later co-opted by predators and prey as a chemical signal.