Termites are among the most successful animals on Earth, forming vast societies that can number in the millions. But how did such complex social systems evolve from solitary ancestors that looked much like today’s cockroaches?

New research from the University of Sydney has uncovered a surprising answer: termites didn’t become more socially complex by gaining new genes, but by losing them – including genes linked to sperm competition. The findings shed new light on the long-standing question of whether monogamy is essential for the evolution of complex insect societies.

The international study, published in Science, traces termite evolution back to ordinary cockroaches – including the ancestors of modern ’domestic’ cockroaches – that began feeding on dead wood. This dietary shift triggered a cascade of genetic and social changes that eventually produced termites and their highly organised colonies.

The study was an international collaboration with researchers from China, Denmark, and Colombia.

“Termites evolved from cockroach ancestors that started living inside and eating wood,” said Professor Nathan Lo from the University of Sydney’s School of Life and Environmental Sciences, a senior author on the paper. “Our study shows how their DNA changed first as they specialised on this poor-quality diet and then changed again as they became social insects.”

To uncover these changes, the researchers sequenced and compared high-quality genomes from cockroaches, woodroaches – a close relative that lives in small family groups – and multiple termite species with different levels of social complexity.

Genetic complexity and monogamy

One of the most striking discoveries was that termite and woodroach genomes are smaller and simpler than those of cockroaches. Many genes linked to metabolism, digestion and reproduction have been lost as termites became increasingly dependent on cooperation and food sharing within the colony.

“The surprising result is that termites increased their social complexity by losing genetic complexity,” Professor Lo said. “That goes against a common assumption that more complex animal societies require more complex genomes.”

The most telling losses were genes involved in building the tail, or flagellum, of sperm. Unlike cockroaches and most animals, termite sperm lack tails and are immotile.

“This loss doesn’t cause monogamy,” Professor Lo said. “Instead, it’s a strong indicator that monogamy had already evolved.”

In most animals, including cockroaches, females mate with multiple males. This creates intense sperm competition, favouring fast-swimming sperm with tails. But once termite ancestors became monogamous, sperm competition disappeared – and sperm tails were no longer necessary.

“Our results indicate that the ancestors of termites were strictly monogamous,” Professor Lo said. “Once monogamy was locked in, there was no longer any evolutionary pressure to maintain genes involved in sperm motility.”

This finding feeds directly into a long-running scientific debate about whether close genetic relatedness is required for complex social systems to evolve. Some researchers have argued that high relatedness is not essential. This study suggests that, at least in termites, monogamy and high relatedness were crucial.

Food-sharing loops support the colony

The research also explains how termite societies are organised from within. Experiments showed that whether a young termite becomes a worker or a future king or queen depends heavily on nutrition during early development.

Larvae that receive abundant food from older siblings develop high energy metabolism and become workers, who don’t reproduce. Those that receive less food grow slowly at first and retain the potential to become reproductives later in life, that is kings or queens.

“These food-sharing feedback loops allow colonies to fine-tune their workforce,” Professor Lo said. “They help explain how termites maintain stable, highly efficient societies over long periods.”

When a termite king or queen dies, monogamy does not end. Instead, the role is usually filled by one of their own offspring, leading to widespread inbreeding within colonies.

“From an evolutionary perspective, that reinforces relatedness even further,” said Professor Lo, who is part of a dynamic and growing insect research group in the School of Life and Environmental Sciences at the University of Sydney.

By combining genomics, physiology and behaviour, the study offers one of the most comprehensive explanations yet for how termites made the leap from solitary cockroach ancestors to some of the most socially complex organisms on the planet.

“This work shows that understanding social evolution isn’t just about adding new traits,” Professor Lo said. “Sometimes, it’s about what evolution chooses to let go.”

Main photo

Physogastric termite queen (top left) of Macrotermes michaelseni being groomed by workers and the larger king, with soldiers in the foreground. Photo by Jan Sobotnik

Research

Cui, Y. et al ‘Nutritional specialisation and social evolution in woodroaches and termites’ (Science 2026) DOI: 10.1126/science.adt2178

Declaration

The authors declare no competing interests. Funding was received from the National Natural Science Foundation of China, the Department of Science and Technology of Guangdong Province and the Australian Research Council.