Costs and benefits in mutualistic associations between ants and phytophagou
s myrmecophiles are context dependent. We collected information from the li
terature on costs and benefits of myrmecophily in aphids, coccids, membraci
ds and lycaenids. A key result of the literature survey is that investment
in mutualism with ants entails costs paid not only when ants are present (d
irect costs) but also when they are absent (indirect costs). We incorporate
d such a trade-off in a model that investigates the fitness consequences of
the decision of a potential myrmecophile whether or not to invest in coope
ration with ants. The model shows that whether myrmecophily should be favou
red depends on the rate of increase of the population, and, if there are in
direct costs, on the frequency of habitats with ants. Both direct and indir
ect costs can limit or prevent the evolution of myrmecophily even when ants
are abundant. To understand the patterns of associations in the field we t
herefore need to measure the benefits and costs of myrmecophily both in the
presence and in the absence of ants.