Mysterious flag-waving behavior in a tropical bug is an anti-predator strategy

If you happen to be walking in the forests of Panama, you might just come across a bug that will wave at you, which scientists at the Smithsonian Tropical Research Institute (STRI) have been studying for a while. The matador bug (Bitta alipes) carries striking, reddish “flags” on its hind legs and performs an intricate leg-waving display. But the reason why these bugs perform this behavior has remained a mystery — until now.

Sexual selection seemed a likely explanation. Males would wave their flags to attract females. Yet when scientists tested the idea, they found no evidence: both males and females waved their legs, and waving was unrelated to courtship or competition. That deepened the puzzle: if not for sex, why evolve such a conspicuous and seemingly costly behavior?

A new study published in Current Zoology by STRI researchers Connor Evans-Blake, Juliette Rubin and Ummat Somjee offers an answer. These colorful “flags” appear not to attract mates, but to deter predators. The team exposed matador bugs to two different arthropods: predatory praying mantids and harmless katydids. They recorded nearly 3,000 leg waves. The results were striking: on average, bugs increased their waving behavior seven-fold in the presence of mantids, but barely responded to katydids. Even more telling, mantids never attacked bugs that were actively waving.

The findings show that waving is an anti-predator behavior, deployed specifically when danger looms. To document whether similar flag-waving behavior occurs in other species within the family, researchers used direct observations in Panama and searched for videos online. They found that at least five related flag-legged species display similar waving behaviors, hinting at a broader evolutionary strategy among these plant-feeding insects.

All these flag-waving insects feed on passionflower vines, known to carry toxins, and may thus be advertising their own chemical defenses with these bold movements. But how does waving reduce predatory attacks? The precise mechanism remains a mystery. Is the waving communicating the bugs’ likely toxicity, confusing predators’ vision, or intimidating attackers with exaggerated motion?

“We’re left with more questions than answers,” said senior author Ummat Somjee. “But that’s the beauty of studying insects — there are hundreds of thousands of species, most of them completely unstudied, and every time we look closely we uncover behaviors that change the way we think about evolution.”

Research like this goes beyond solving quirky puzzles. Insects make up the majority of Earth’s biodiversity and are foundational to terrestrial ecosystems worldwide, yet most of their behaviors remain undocumented. Understanding how prey defend themselves provides insight into how animals evolve and diversify into the many forms, sometimes bizarre, that make up complex ecosystems.

Reference: Evans-Blake, C., Rubin, J. J., & Somjee, U. (2025). Flag-waving behavior in matador bugs is an antipredatory strategy. Current Zoology, zoaf047.

About the Smithsonian Tropical Research Institute

Headquartered in Panama City, Panama, STRI is a unit of the Smithsonian Institution. Our mission is to understand tropical biodiversity and its importance to human welfare, to train students to conduct research in the tropics and to promote conservation by increasing public awareness of the beauty and importance of tropical ecosystems. Watch our video, and visit our website, Facebook, X and Instagram for updates.