With Valentine’s Day around the corner, Lepidoptera love is in the air. When it comes to finding and courting a mate, moths and butterflies have some interesting (and some frankly bizarre) habits.
Love songs
We all know that birds sing to attract mates, but some moths also sing as part of courtship. Examples have been found in many parts of the world and in several moth families (e.g. Pyralids, Crambids, Noctuids and Erebids), with more undoubtedly waiting to be discovered. In all these musical moths, it is the males that sing, producing ultrasonic calls (think Jimmy Somerville rather than Barry White!) usually after first locating their mates by smell.
However, this is not necessarily the romantic serenade one might imagine. Researchers have shown that the males of the Asian micro-moth Ostrinia furnacalis (a close relative of the European Corn-borer O. nubilalis that occurs in southern Britain) trick the females, who cannot distinguish the song from the hunting calls of bats. The male’s song therefore causes the female to freeze (predator avoidance behaviour), significantly increasing his chance of mating with her. This is not always the case though. In a species of footman moth (Eilema japonica), the females can distinguish between the ultrasonic calls of amorous males and hungry bats.
Scent with love
Unlike in butterflies, which mainly recognise each other by sight, most moths (especially nocturnal species) find each other by scent. Typically, female moths call to males by releasing pheromones from glands at the end of their abdomen. These chemical messages are species-specific and are carried in a scent plume by the wind over considerable distances. Male moths detect the scent using their antennae (which are strongly ‘feathered’ in many species to provide a very large surface area of sensory receptors) and then fly towards the source of the smell. It is said that male Emperor moths are able to respond to a calling female from several miles away, but typically pheromones will be effective over 100m or so. Once the happy couple have found each other, males of some moth species also produce pheromones to signal to their potential mate.
Butterflies also make use of scent in courtship. Males of some butterfly species (e.g. Silver-spotted Skipper, Large Skipper, Silver-washed Fritillary) have special structures, called sex-brands or androconial organs, on their forewings that produce scent. During courtship, male butterflies often position themselves face to face with their potential partner and draw the female’s antennae over the sex-brands on his wings. Female butterflies can also use pheromones, at short range, to encourage male suitors.
Bag of tricks
When it comes to reproduction, the bagworm moths (micro-moths in the family Psychidae) have perhaps the weirdest habits of any UK Lepidoptera. The caterpillars of these species live in silken cases (hence the name bagworm) which are often decorated with small pieces of plant material or even bits of dead insects. The adult males are normal moths, but the females of many bagworm species are wingless. Having pupated in the larval case, the wingless females remain in or on the case and use pheromones to attract a mate. Eggs are often laid in the larval case. A few species do not even need to mate; females can produce female offspring by parthenogenesis.
Perhaps the strangest tricks of this odd group are employed by Acanthopsyche atra and Pachythelia villosella. The females of these species are not only wingless, but also limbless and look and move like fly maggots. Once mated, these extraordinary female moths leave the case and wriggle about, seemingly in a deliberate attempt to attract bird or lizard predators. Experiments have shown that the moths eggs can pass right through the digestive system of such predators and successfully hatch out afterwards. It seems that the female moths are using predators to disperse their offspring just as many fruit-producing plants do.
Richard Fox
Head of Recording
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