LIGHT, PREDATION AND THE LEKKING BEHAVIOR OF THE GHOST SWIFT HEPIALUS-HUMULI (L.) (LEPIDOPTERA, HEPIALIDAE)

We examined the timing of the crepuscular lekking flight of male ghost swift moths in southern Sweden with respect to variations in: (i) the quality of the visual mating signal; and (ii) the behaviour of potent ial vertebrate predators (mainly bats). The moths' display flights sta rted ca. 57 min after sunset, and occurred during 20-30 min at inciden t light intensities between 10.0 and 2.0 lux. Owing to the falling and more shortwave ambient light after sunset, the brightness contrast be tween the moth wings and the background (grass) increased steeply at t he time of display onset. The silvery white male wing colour thereby s eems to maximize conspicuousness, and may be a secondary adaptation th at facilitates visibility at low light intensities. The display timing itself is probably determined by other factors, possibly predation. B y displaying only for a short period at dusk, the moths seem to avoid most birds, which normally do not forage at these light levels, and gl eaning bats, which typically do not start to feed until the light inte nsity has fallen even further. Nevertheless, aerial-hawking bats were often (54% of the evenings, n=22) seen at the leks, and one species (E ptesicus nilssonii) frequently fed on the displaying moths (22% of the moths observed, n=83). H. humuli represents an ancient clade among th e Lepidoptera. By restricting its sexual behaviour to a short time win dow at dusk, when predation risk may be, minimized (but still high), i t may to some extent compensate for the lack of sophisticated predator defence systems such as aposematic or mimetic coloration, manoeuvrabl e flight, and ultrasonic hearing, which predominate among the more rec ent Lepidopteran clades. However, the time window solution restricts t he moths' activities considerably and the lack of defence still carrie s a considerable cost in terms of predation.