Sexual cannibalism is well-documented in insects and spiders, like praying mantises or black widows. In these cases, the female usually cannibalizes the male, so only one partner benefits from this behavior because the other is dead.
But a new study published in the journal Ethology suggests both mates can partake in what's called nuptial feeding and still live happily ever after together, in sickness and health, without tragedy—or at least, wood-feeding cockroaches (Salganea taiwanensis) can.
These love bugs are already monogamous, so they mate for life and never stray from the rotten log they call home-sweet-home to find another sweetheart. To really seal the deal, the roaches devour each other's wings post-sex, a behavior that could boost their ability to co-parent and raise more offspring, reports Joshua Rapp Learn for New Scientist.
Sacrificing their wings doesn't make the individuals stronger, but it could benefit the species in the long run. Without wings, the cockroaches can no longer fly, which eliminates one of their best resources for escaping predators and finding food. (So even if one of the cockroaches did have a wandering eye, they wouldn't last long on their own.) With nowhere to go safely and limited options for scavenging, these two wingless lovers don't have many options besides sticking together, making lots of babies and raising their young together.
For evolutionary purposes, teaming up to devote their lives to reproduction is not a bad idea.
“It makes sense that there’s an advantage to getting rid of your wings if you’re not going to fly ever again,” says Allen J. Moore, an evolutionary biologist at the University of Georgia who was not involved in the study, to Elizabeth Preston for the New York Times.
Study co-author Haruka Osaki, a biologist at Kyushu University in Japan, first observed the wood-feeding roaches in the wild and noticed that some insects had missing or damaged wings, according to the New York Times. After further research, Osaki learned the wing damage did not occur from predation, but from roaches feasting on each other’s wings in an act of mutual sexual cannibalism.
To determine why this behavior occurs, Osaki and her team collected cockroaches from forests in Okinawa, Japan, and paired them off into 24 couples back in her lab, reports New Scientist. Osaki recorded the roaches for three days with video cameras and observed that the cockroaches taking turns cannibalizing each other’s wings, the New York Times reports. Twelve pairs ate each other’s appendages completely.
This wing-eating behavior is still rather rare within the species itself, monogamy in insects is also rare and the roaches are one of the only known species that engage in mutual sexual cannibalism, reports New Scientist. While similar to nuptial feeding and sexual cannibalism, the reciprocal cockroaches behavior differs in two major ways. Both males and females engage in eating each other’s wings and live to tell the tale. The wings also lack nutritional value, so they don't seem to engage in this behavior from lack of food, according to the study.
While researchers still do not fully understand why the roaches engage in this behavior, they suspect that the action occurs because it benefits both male and female insects while raising offspring, aids in their survival, and stems from their monogamy, New Scientist reports.
Wing loss is costly, but the event can also help them slim down to maneuver around in tight spaces within their home. It may also rid them of mites and mold that otherwise might infect their wings, which in-turn protects their offspring from picking up any hitchhiker they were caring.
“This wood-feeding cockroach must benefit somehow because this behaviour has evolved and maintained,” says Osaki to New Scientist.