Ants Know Friend or Foe by Scent

If you are human, knowing one's enemies is easy. The brain evaluates another person as to whether he/she is friendly or not. It may be necessary to work alongside an enemy but the enemy tag still remains. Insects do not have have such advanced brain power to discriminate friend or foe.

Ants need a frame of reference to identify who they have to attack. When an ant from a colony meets an ant from another and they fight, the ants keep a memory of the enemies' odor. This occurs even though they may be of the same species. The "smell of fear" is passed on to fellow ants in the same colony. Ants also use scent to know other ants in their colony.

In tests individual ants were familiarized with individuals from another colony. They could see each other. Actual contact was prevented. When 20 intruders were placed near to the other colony they were attacked despite attackers knowing the other ants.
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