A host can sometimes utilize the mafia effect, i.e. a strategy that is otherwise used by a number of parasitic species. This strategy consists in that the parasite does not damage its host much until the host begins to effectively to defend itself. As soon as the host initiates a defense mechanism, the parasite somehow “penalizes” it (Gadagkar & Kolatkar 1996). This phenomenon is most marked in cases where the interaction of a host with a parasite takes place at an ethological level. The cuckoos of some species remain in the vicinity of nests in which they lay their eggs and watch how the host bird acts toward their eggs. If the host throws the foreign egg out of the nest, then the cuckoo breaks all the eggs in the nest during the next inspection. It is thus better for the host to leave the egg alone because, for this species of cuckoo, the young bird does not destroy the whole brood and thus parents that tolerate the cuckoo have a chance of bringing up at least some of their progeny. Consequently, selection prefers birds that are not able to recognize a foreign egg in their nest or at least tolerate it (Zahavi 1979; Soler et al. 1995). A quite analogous strategy is apparently employed by a number of pathogenic organisms, including bacteria (Soler, Moller, & Soler 1998). A great many bacteria begin to release toxins only when they are attacked by the immune system of the host organism or when the host organism prevents them from having access to some essential resource, very frequently iron.
The attacked host can also use the mafia effect in the above-described host – parasite – hyperparasite interaction. If the parasite does not damage it much, it is better to tolerate it. In plants, the presence of a benign parasite (microherbivore) can even protect the plant against other, more dangerous species (Saikkonen et al. 1998). If the parasite were to greatly damage it, it would attract hyperparsites and predators that destroy the parasite. In this case, once again, the species or lines of parasites that greatly damage their host are eliminated. Mathematical models indicate that a mechanism based on the mafia effect can be relatively easily fixed in a population and that, for example, when destruction of the egg batch does not require any great effort on the part of a cuckoo, this will even be an evolutionarily stable strategy (Soler, Moller, & Soler 1998).