In a study published Monday in the Proceedings of the National Academy of Sciences, researchers show that the hornworm uses this "defensive halitosis" to keep away it's primary predators -- wolf spiders.
The worm chews the coyote tobacco plant all day, ingesting as much as a milligram of nicotine -- equivalent to a cigarette. The hornworm is one of the few insects immune to nicotine, which is known to paralyze others.
Researchers at the Max Planck Institute for Chemical Ecology said the worm stores nicotine in its blood and then exhales a small amount using its spiracles, respiratory openings running along its body.
Researchers placed a nicotine-laced worm in a cup and observed that a wolf spider refused to go near the worm, despite being ravenously hungry. The wolf spider had no problem eating the worm fed nicotine-free tobacco or genetically modified tobacco that silenced this "bad breath."
"Spiders usually assess their prey after capture by tapping it with chemosensory endowed legs and palps," the authors wrote. "Wolf spiders were clearly rejecting nicotine-fed larvae before penetrating their prey with their mandibles to inject their mixture of digestive enzymes and poisons."
At a research ranch in Utah, researchers planted regular coyote tobacco and nicotine-free tobacco and placed the hornworms on them to study survival rates.
The caterpillars on the nicotine-free tobacco were found to disappear much more quickly at night than their counterparts, with the wolf spider singled out as the primary suspect. But another predator of the caterpillar, called the big-eyed bug, hunted during the day and showed no aversion to the nicotine-fed worms.