Night of the Living Ants
When an ant dies，other ants move the dead insect out of the nest．This behavior．is interesting to scientists，who wonder how ants know for sure-and so soon-that another ant is dead．
Dong-Hwan Choe，a scientist at the University of California，found that Argentine ants have a chemical on the outside of their bodies that signals to other ants，“I’m dead-take me away．”
But there's a twist to Choe's discovery．Choe says that the living ants-not just the dead ones -have this death chemical．In other words，while an ant crawls around，perhaps in a picnic or home，it's telling other ants that it's dead．
What keeps ants from hauling away the living dead?Choe found that Argentine ants have two additional chemicals on their bodies，and these tell nearby ants something like，“Wait-I'm not dead yet．” So Choe's research turned up two sets of chemical signals in ants：one says，“I'm dead，”the other set says，“I'm not dead yet．”
Other scientists have tried to figure out how ants know when another ant is dead．If an ant is knocked unconscious，other ants leave it alone until it wakes up．That means ants know that unmoving ants can still be alive．
Choe suspects that when an Argentine ant dies．the chemical that says“Wait-I'm not dead yet” quickly goes away．Once that chemical is gone，only the one that says“I'm dead”is left．“It's because the dead ant no longer smells like a living ant that it gets carried to the graveyard(墓地)，not because its body releases new，unique chemicals after death，”said Choe．When other ants detect the“dead”chemical without the“not dead yet”chemical，they haul away the body．This was Choe's hypothesis(假设)．
To test his hypothesis，Choe and his team put different chemicals on Argentine ant pupae(蛹)． When the scientists used the“I'm dead”chemical，other ants quickly hauled the treated pupae away． When the scientists used the“Wait-I'm not dead yet”chemical，other ants left the treated pupae alone． Choe believes this behavior．shows that the“not dead yet”chemical overrides(优胜于)the“dead”chemical when picked up by ants．And that when an ant dies，the“not dead yet”chemical fades away． Other nearby ants then detect the remaining“dead”chemical and remove the body from the nest．
The phrase“this death chemical”in paragraph 3 refers to