Englishman Henry Walter Bates, a contemporary of Charles Darwin, was the first scientist to show that animals can defend themselves in the wild by resembling predators or stronger species. After spending a decade in the Amazon rain forest, Bates noticed “flies that looked like bees, beetles that looked like wasps, even caterpillars that looked like pit vipers.” He determined that animals defended themselves in the wild by using mimicry, concealment, a display of warning colors or even by masquerading as inedible objects.
But scientists were never sure exactly how the disguises worked — were the animals concealing themselves or were they hiding in plain sight, just dressed up? Recently, the New York Times reported on a new experiment designed to answer this question. Biologists John Skelhorn and Graeme D. Ruxton at the University of Glasgow and Hannah M. Rowland and Michael P. Speed at the University of Liverpool devised a test to determine if animals were saved by concealment or misidentification. They used the twig-imitating caterpillars of the brimstone moth in their trials.
How was this experiment conducted? The NY Times reports that researchers used young chickens divided into groups. One group was exposed to a hawthorn branch, where the twig-like caterpillars commonly live and disguise themselves. Another group was shown branches laced with an appearance-altering colored thread, and a final group saw an empty cage.
The findings were revealing. The potential predators only fell for the ruse if they had first been exposed to the real deal. Birds that had encountered the hawthorn branch thought the twig-like caterpillars were actual twigs, even at close range. Birds that had never seen the hawthorn branches went straight for the bugs. Masquerading seems to be the way these bugs avoid getting eaten.
Darwin called Henry Walter Bates’ work “one of the most remarkable and admirable papers I ever read in my life.” Luckily for twig-bugs, chickens don’t read.
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