Variety is the spice of humble moth's sex life

December 22, 2014

A small brown moth has one of the most complex sex lives in the insect world, new research has found.

The twilight courtship rituals of the gold swift moth (Phymatopus hecta) can be seen in summer across northern Europe and Asia, from the British Isles to Japan.

Despite the insect's unassuming appearance, a new study published in the Biological Journal of the Linnean Society reports a variety and complexity in its mating patterns and sexual positions worthy of an insect Karma Sutra.

Professor John Turner, Emeritus Professor in the University of Leeds' School of Biology, said: "With most insects, you expect to find a fairly set mating process. In moths like this, you might see the female staying still, emitting a scent and then mating with the first male moth to arrive.

"The love life of the gold swift moth is a veritable Karma Sutra of mating patterns and positions. Colleagues have commented that this is the most elaborate mating procedure known in any insect and I have certainly not observed anything to surpass it."

Professor Turner identified an array of different courtship "dances", with some individuals able to switch to alternative methods if their first gambits were frustrated: Professor Turner also observed frequent "fighting dances" between males and occasional "homoerotic" courtships, where males embarked on mating procedures with members of their own sex. He suggested that the latter might have been triggered by scent from nearby females confusing the males.

There were so many courtship patterns that categorising them became difficult. Professor Turner said: "I intervened on some occasions to stop the mating. The insects would pause and then resume using a different pattern. It started to look a bit like a human courtship, with the moths doing it every which way and having a whole range of tactics for attracting a mate."

There was also unexpected variety in the moths' sexual positions. Unlike most insects, which stick rigidly to a single position, the gold swift moth had two approaches: Variations on the two main positions were also observed.

The paper concludes that the complexity is evolutionarily stable and has probably persisted in the species for tens of thousands of years. An individual moth that limited its mating approaches -- for instance, a female losing the ability to produce scent -- would reduce its mating options.

A possible explanation for the complexity of the moth's sex life may be the relative scarcity of its mating grounds, which means that both males and females congregate together in restricted areas. This confused environment may encourage the development of a variety of ways of finding a mate, using both visual and olfactory stimuli.

Professor Turner conducted the study during holidays in the north of Scotland.

He said: "I was doing the washing up and I looked out of the kitchen window to see all this happening in the vegetation in front of me. Over the next seven years, I studied it every time I came to Scotland. One of the reasons this has not been reported before may be that it happens in the twilight. There are not that many people looking at insects at that time: all the butterfly people have gone to the pub and the other moth people haven't switched their torches on yet."
-end-
Further information

Professor Turner is available for interview.

Contact: University of Leeds press office on +44 113 343 4031 or email pressoffice@leeds.ac.uk.

The full paper: John R. G. Turner, 'The flexible lek: Phymatopus hecta the gold swift demonstrates the evolution of leking and male swarming via a hotspot (Lepidoptera, Hepialidae)' is published in Biological Journal of the Linnean Society 2014 (DOI 10.1111/bij.12411; URL http://onlinelibrary.wiley.com/doi/10.1111/bij.12411/pdf) and is available for download.

University of Leeds

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