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Japanese researchers find wood-feeding cockroaches munch each other's wings when mating

This drawing by Haruka Osaki shows a wood-feeding cockroach pair eating each other's wings. (Image courtesy of Haruka Osaki)

TOKYO -- Researchers in Japan have confirmed that pairs of wood-feeding cockroaches chow down on each other's wing when mating -- apparently the first time mutual cannibalism between mates has been observed in the natural world.

    Unilateral cannibalism among species such as praying mantises, whose females eat the males, has long been known.

    Wood-feeding cockroaches live inside rotting trees in forests in southwestern Japan's Kyushu region and other southern islands, and come out of the trees only during breeding season between April and July to find mates. The insects lay their eggs in tunnels they burrow into their trees, and both parents provide the baby cockroaches, or nymphs, a liquid food they produce from their mouths.

    Kyushu University (Mainichi/Yusaku Yoshikawa)

    Kyushu University graduate school student Haruka Osaki and associate professor of ecology Eiiti Kasuya collected nymphs of S. taiwanensis ryukyuanus, a species of wood-feeding cockroach, on Okinawa Prefecture's main island. They set up 24 male-female roach pairs, and observed their behavior for three days each.

    The researchers observed 12 of the pairs engaged in eating their mate's wings after touching them with antennae and licking their bodies. Both males and females repeated the behavior, and on average about 70% of their wings were consumed. Which of the sexes ate the other's wings first varied among the pairs.

    As their wings do not regenerate, the cockroaches cannot fly after eating each other's wings. Though wood-feeding cockroaches without wings had been found in field studies, researchers had suggested they had been scraped off inside the rotten trees, among other possible reasons.

    Wood-feeding cockroaches are monogamous, and mating pairs apparently never cheat. Researchers speculate that the pairs staying flightless and hidden in their trees may be advantageous when it comes to providing more food to their nymphs and producing more offspring. Because there is little muscle in the wings, it is unlikely that they eat each other's wings for nutrition.

    "They have a low habitat density, so difficulty finding mating partners may be behind the behavior," Osaki said. "I would like to uncover their evolutionary process, including finding what conditions led to them developing this behavior of eating each other's wings."

    The study has been published in the animal behavior journal Ethology (https://onlinelibrary.wiley.com/doi/10.1111/eth.13133)

    (Japanese original by Ai Oba, Science & Environment News Department)

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