Some caterpillars'  warning signals may have evolved   from walking.      A team, writing in the journal Nature Communications, reported that the hair-like structures   the creatures use to make sounds evolved from legs. The team studied caterpillars which use these structures to communicate their ownership of leaves. This means the caterpillars are able to "tell" strangers to go away without risking injury in conflicts. "These are really interesting caterpillars," said Dr. Jayne Yack from Carleton University in Ottawa, Canada, who led the research. "They make signals using hair-like structures which are on their back ends." The caterpillars drag these structures across the leaf to make scraping  sounds when strangers enter their "leaf shelters". "When they make this signal, the strangers leave," explained Dr. Yack. "It's like saying 'I'm here, get out of here --I already own this leaf'." The scientists looked at other species within the same group of caterpillars and created a "family tree" of the creatures. They used chemical markers to work out the relationship between the animals, showing which in the group were the more ancient species and which species evolved more recently. "Those more ancient species actually don't have these sound-producing structures. They have legs that they use to walk towards strangers," said Dr. Yack. These more ancient species, she explained, walk towards strangers and try to attack them. "They can kill each other in the conflicts," Dr. Yack added. She said that the evolution of the scraping show had allowed the caterpillars to solve their conflicts without fighting. "So our idea is that these signals actually avoid damage to both sides --they solve conflicts in a more 'friendly' way." The study also provides a map of an evolutionary path that many other biologists are exploring. Caterpillars that evolved more recently warn strangers by   _  .
attacking them with their legs making scraping sounds walking around the leaves they own releasing a kind of chemical