For certain cockroaches living inside rotten logs in Asia, nothing says I love you like some minor cannibalism. Newly mated pairs of 1 species alternate chewing each other’s wings right down to stubs after they enter the homes where they’re going to jointly raise babies. Scientists say this unique behavior may have evolved due to the roach’s truly monogamous bond. Haruka Osaki, who published the finding last month in Ethology, first happened upon some wingless roaches in 2014. She had been collecting insects from the woods as a hobby since becoming a biology student at Kyushu University in Japan the previous year. “When I caught the wood-feeding cockroaches within the wild, I noticed that their wings were chewed by something Ms. Osaki said.

When it had been time to settle on a subject for her doctoral research a few years later, Ms. Osaki thought of the roaches. She knew from others’ observations that the damage probably didn’t come from predators, but from cockroaches eating each other’s wings. But she didn’t know why. Her adviser, Eiiti Kasuya, encouraged her to dive in. Ms. Osaki collects her study subjects, which as adults have dark, glossy bodies about an in. long, from the wild. I walk into the Okinawan forest and look for rotten logs, she said. The cockroaches sleep in tunnels in rotten wood, so I destroy the wood with a hatchet and pick them up. She packs the roach colonies into containers, then flies with them back to her laboratory in Fukuoka.

After a number of her young, wild-caught cockroaches matured into adults, Ms. Osaki paired them off within the lab, creating 24 couples. Then she recorded their behavior with video cameras for 3 days. The videos revealed that the roaches ate each other’s wings piecemeal. One bug would hop on the other’s back and eat, while the opposite sat motionlessly. Then they took an opportunity before they resumed, sometimes swapping positions.

At times, the cockroach being munched on gave a violent shudder, which appeared to encourage the muncher to require an opportunity. But the cockroaches otherwise didn’t seem to mind having their appendages gnawed off. Twelve of the couples ate each other’s wings completely. Wood-eating cockroaches aren’t the sole creatures that make a meal out of their mates, but their motivations could also be unique.

Cannibalism is sort of frequent in spiders said María José Albo, an evolutionary biologist at the University of the Republic in Uruguay. Among sexually cannibalistic spiders and insects like praying mantises, it’s usually a bigger female who eats her mate. Although on the surface it looks like a nasty outcome for the male he may benefit by transferring more sperm while the feminine dines, Dr. Albo said. On a less gruesome note, Dr. Albo added, some male insects and spiders give their mates a so-called nuptial gift of food that’s sometimes made up of the male’s own body. The gift may buy him longer to mate or to flee.

All of those cases involve just one mate being fed, Dr. Albo said, which makes the cockroaches so unusual. If the mutual wing-eating has fitness benefits for both sexes, it’ll be the primary cause of mutual gift-feeding she said. hose benefits probably aren’t nutritional, Ms. Osaki and Dr. Kasuya wrote, because the cockroach wings aren’t fleshy. But the roaches probably do enjoy losing their wings, because wings are cumbersome when living in tight quarters. Wings also can collect mold or mites, the authors wrote.

“It is sensible that there’s a plus to getting obviate your wings if you’re not getting to fly ever again,” said Allen J. Moore, an evolutionary biologist at the University of Georgia. other insects that live underground or inside wood also shed their wings after mating, like termites, close relatives that Dr. Moore called just fancy cockroaches. But these insects need to lose their wings on their own. This mutual helping is simply special he said. Dr. Moore agreed with the authors that the cockroaches’ cooperative behavior presumably stems from their monogamy.

Once they’re coupled, the roaches will nevermore leave their rotten log or encounter other potential mates. From an evolutionary standpoint, they share equivalent interests. They both want to remain alive and look out for their young. The cockroaches have also been observed guarding their babies against predators and even feeding them fluids from their own mouthparts, as birds do.) the oldsters may also cooperate, and that they start by helping one another shed their wings. essentially, the cockroach partners could also be scratching each others’ backs with their mandibles. If this is often confirmed, it’ll be a rare example in the nature of mates that really want an equivalent thing, Ms. Osaki said, adding, “Sexual conflict has been always assumed.