Figure 1.

Bio-communication through light. Communication via visible part of electromagnetic spectrum is common in nature. Many organisms communicate by light reflected from their bodies, like strawberry poison frogs Dendrobates pumilio(A). Some organisms, for instance fireflies, are also able to generate light for the purpose of communication (B). However, electromagnetic communication between single cells is a subject to speculations (an artist view C). (Attribution: A - Davepape at en.wikipedia, B - Emmanuelm at en.wikipedia).