The role of size and colour pattern in protection of developmental stages of the red firebug ( Pyrrhocoris apterus ) against avian predators

We investigated how predator/prey body‐size ratio and prey colour pattern affected efficacy of prey warning signals. We used great and blue tits ( Parus major and Cyanistes caeruleus ), comprising closely related and ecologically similar bird species differing in body size, as experimental predators. Two larval instars and adults of the unpalatable red firebug ( Pyrrhocoris apterus ), differing in body size and/or coloration, were used as prey. We showed that prey body size did not influence whether a predator attacked the prey or not during the first encounter. However, smaller prey were attacked, killed, and eaten more frequently in repetitive encounters. We assumed that body size influences the predator through the amount of repellent chemicals better than through the amount of optical warning signal. The larger predator attacked, killed and ate all forms of firebug more often than the smaller one. The difference between both predators was more pronounced in less protected forms of firebug (chemically as well as optically). Colour pattern also substantially affected the willingness of predators to attack the prey. Larval red–black coloration did not provide a full‐value warning signal, although a similarly conspicuous red‐black coloration of the adults reliably protected them. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 890–898.