Pruning bug genitals revives puzzle of extra-long males

seed bug penis and tip

The sperm-delivery organ (left) of a Lygaeus simulans bug ends in a tough, elongated tube (right). Experimentally shortening the tube might someday explain why male and female lengths don’t seem to match.


L.R. Dougherty et al./Proceedings B 2015

Small red-and-black bugs with male sex organs more than 70 percent the length of their bodies turn out to have an unusual tolerance for surgical shortening.  

The sperm-delivery organs of Lygaeus simulans bugs start fleshy but become just a long, toughed tube with no apparent nerves or muscles. Snipping up to 2 millimeters off this 6- to 7-milimeter-long tube leaves a structure that’s at least twice as long as the female bug’s reproductive duct. Yet having only a double-long structure reduces a male’s chances of inseminating a female during a tryst from about 50 percent to about 10 percent, researchers say May 13 in Proceedings of the Royal Society B.

The effects of the shortening alone don’t explain the reduction, says paper coauthor Liam Dougherty of the University of St. Andrews in Scotland. Snipping just the wee tip off or even 0.4 millimeters didn’t seem to make a difference. Dougherty anesthetizes the males before the procedure and when they revive, they seem as eager as ever to mate. “I don’t think they know what’s happened to them,” he says.

Discovering that males tolerate the surgery provides a new technique for exploring the evolution of this puzzling mismatch between his and hers lengths, Dougherty says. His and others’ work has established that for these male bugs, longest is not best. Those with average natural lengths had better chances of inseminating females than those either a half of a millimeter too short or too long.

Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.

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