Conspicuous colouration is often associated with the presence of toxic or distasteful defense substances. Species producing poisons might profit from advertising the presence of those compounds. If a conspicuous colour can be associated behaviorally with an unpleasant experience, the predator might avoid the prey upon a second encounter. Natural selection thus favours variants that have conspicuous colouration and live long enough to reproduce and spread the conspicuous colour trait in the population. Therefore, one can assume that conspicuous colours are mostly associated with the presence of toxic and bad-tasting compounds that warn potential predators that the animal is full of distasteful chemicals and not worth attempting to eat. This warning display strategy is known as aposematic colouration. Yellow and black can be considered a very alarming and successful colour combination for deterring putative predators. It is found not only among pseudocerotid flatworms but also on frogs, salamanders, nudibranchs and arthropodes such as spiders and many insects. In most cases, this colour combination is associated with poison or irritant defense chemicals. The occurrence of yellow-black colour combination in so many different taxa is an outstanding example for analogous evolution (e.g. unrelated species have developed the same distinct phenotype because of a similar selective pressure).

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Last update: April 9, 2002