A new US study may make you think twice about biting into a piece of lettuce . Scientists claim plants can feel themselves being eaten alive – and some can even tell what type of creature is attacking them . The discovery was made after tests on the Arabidopsis plant found it can distinguish between insects eating it based on the way they chew and drool . Scroll down for video . A new US study may make you think twice about biting a piece of lettuce.Scientists claim plants can feel themselves being eaten alive – and some can even tell what type of creature is attacking them . 'It was no surprise that plants responded differently to having their leaves chewed by a caterpillar or sucked by an aphid , ' Heidi Appel , senior research scientist University of Missouri told the Washington Post . 'What surprised us was how different plant responses were to each of the caterpillars and aphids . The plants could clearly tell insects apart - they really seem to `` know '' who 's attacking . ' Professor Appel exposed a group of Arabidopsis , which is part of the cabbage family , to cabbage butterfly caterpillars and beet army worms . She predicted that as the insects eat the plant , Arabidopsis could tell by the chewing motion and the drool whether the creature was a butterfly or a worm . Heidi Appel ( left ) and Rex Cocroft ( right ) previously conducted a study that found plants can identify sounds nearby , such as the sound of eating , and then react to the threats in their environment . She also believed that the plant could tell several different insects apart , even when they were eating the leaves simultaneously . To test her theory , she harvested the chewed up Arabidopsis , extracted the genes , and froze it in a laboratory . Plants attempt to defend themselves using different methods , such as giving off spicy flavours and rancid smells . These defences are expressed in their genes . Researchers in Bonn , Germany , found plants give off a gas when under 'attack ' . Super-sensitive microphones picked up a 'bubbling ' sound from a healthy plant . But this rose to a piercing screech when it was under threat . Even a tiny insect bite could have an effect . 'The more a plant is subjected to stress , the louder the signal , ' said Dr Frank Kühnemann . Plants do not actually scream in pain . But different sounds are heard when the gas they emit , ethylene , is bombarded with lasers . The research could help to work out which pieces of fruit and vegetables are likely to stay fresh longer , as a cucumber which is starting to go off produces a squealing sound . It could then be separated from the fresher ones . Based on the gene analysis , Professor Appel found that the plant can sense when a caterpillar is drooling and provides a different defence mechanism , than if it sensed a butterfly . There were also different genetic responses to each worm , showing that the plant knew what was eating it . Professor Appel hopes that this will allow scientists to breed plants that are naturally insect resistant rather than spraying them with pesticides . The research builds on a study last year that found plants can identify sounds nearby , such as the sound of eating , and then react to the threats in their environment . In this study , caterpillars were placed on Arabidopsis . Using a laser and a tiny piece of reflective material on the leaf of the plant , scientists measured the movement of the leaf in response to the chewing caterpillar . Professor Appel then played back recordings of caterpillar feeding vibrations to one set of plants , but played back only silence to the other set of plants . When caterpillars later fed on both sets of plants , the researchers found that the plants previously exposed to feeding vibrations produced more mustard oils , a chemical that is unappealing to many caterpillars . 'What is remarkable is that the plants exposed to different vibrations , including those made by a gentle wind or different insect sounds that share some acoustic features with caterpillar feeding vibrations did not increase their chemical defences , ' co-author Rex Cocroft , said . 'This indicates that the plants are able to distinguish feeding vibrations from other common sources of environmental vibration . '
Scientists exposed the Arabidopsis plant to caterpillars and worms . They found caterpillars produce more drool when eating a plant leaf . Score: 6