Ecological traps are maladaptive behavioural scenarios in which animals prefer to settle in habitats with the lowest survival and/or reproductive success. Aquatic insect species, for example, are attracted to sources of horizontally polarized light associated with natural water bodies, but today they commonly prefer to lay their eggs upon asphalt roads and buildings that reflect an unnaturally high percentage of polarized light. Ecological traps are a rapidly emerging threat to the persistence of animal populations, but the degree to which species vary in their susceptibility to them remains uninvestigated. We designed a field experiment to (1) assess the relative susceptibility of aquatic flies (Diptera) to a single maladaptive behavioural cue: variation in degree of horizontally polarized light (d), and (2) quantify how the isolation of an ecological trap from a high-quality habitat affects its relative attractiveness. We exposed wild dipterans to experimental test surfaces varying in d at three distances from natural streams and mapped behavioural reaction norms of habitat preference as a function of d and distance from high-quality habitat. All seven of the dipteran families were captured most in traps with progressively higher d values, especially those (d = 90–100%) that exceeded that of natural water bodies (30–80%). In most taxa, the height and slope of numerical responses to d were influenced by the distance of an ecological trap from a natural water body. Our results illustrate that dipterans have broadly evolved the use of a habitat selection behaviour that treats more strongly polarized light sources as indicative higher-quality habitats, making them broadly susceptible to ecological traps driven by polarized light pollution. We also found that the spatial isolation of ecological traps from higher-quality, but less attractive, habitats can either increase or reduce species' susceptibility to them.