In a small acrylic arena lined with chewed wood, two wood-feeding cockroaches circle each other. One bites into its partner’s wing. The other returns the favour. Within hours, both insects have ragged wing stumps — and a new alliance. Any unfamiliar cockroach that wanders in is met with fierce ramming attacks from both residents. Yet the paired cockroaches never attack each other.
Mating pairs of Salganea taiwanensis exhibit exclusive rejection of potential alternative mates following pair formation through their unique mating behaviour: mutual wing-eating, researchers report in a paper published in the journal Royal Society Open Science. After the ritual, both males and females consistently repelled intruders of either sex while never attacking or replacing their established partner.
Pair bonds are usually studied in birds, mammals, and fish, where mates stay close, share space, and drive off rivals. Invertebrates have rarely been tested the same way. The wood-feeding cockroach S. taiwanensis was a strong candidate because of its unusual mating ecology: partners eat each other’s wings, then build a nest together, raise young side by side, and breed for years.
To test whether wing-eating creates true partner-specific behaviour, the team collected colonies from Okinawa, Japan, and formed new adult pairs in the laboratory. They watched 14 pairs complete mutual wing-eating within 24 hours and compared them with 8 pairs that had not yet performed the ritual. Each pair was placed in a nest chamber connected to a side chamber. After 10 minutes, an unfamiliar adult — male or female — was released from the side chamber. Video recorded every push, retreat, and cooperative action for 90 minutes. The next day, each pair faced an intruder of the opposite sex.
Post-eating pairs were far more likely to attack than pre-eating pairs. Every copulated post-eating pair rammed intruders hard, showing both same-sex and opposite-sex aggression. Pre-eating pairs almost never fought. Across 12 intersexual fights, residents delivered 440 ramming attacks; only two were accidentally aimed at the mate, and both stopped instantly. No resident ever copulated with an intruder.
The aggression happened almost entirely inside the nest area. After driving an intruder out, residents sometimes blocked the entrance with sawdust. When one partner fought a same-sex intruder, the other often waited, then joined to attack the opposite-sex intruder. The longer the first fight lasted, the more likely the second attack became. Males and females showed equal levels of aggression and support behaviours such as digging and abdominal wagging.
“Our study demonstrates that S. taiwanensis exhibits the key behavioural features associated with pair-bonded systems, namely selective aggression toward intruders and tolerance toward established partners following pair formation,” the researchers write. “This study provides the first experimental demonstration of selective aggression as a behavioural component of selective social association in an invertebrate.”
“These findings show that exclusive, cooperative partnerships, once thought to be largely a vertebrate phenomenon, can also arise in socially monogamous insects,” they note.
Citations
Haruka Osaki et al. Exclusive aggression against intruders in cockroach mating pairs following mutual wing-eating. Royal Society Open Science. Published online March 4, 2026. DOI: 10.1098/rsos.251992
