Suicidal Ants

http://www.stnews.org/News-1301.htm

When the experts looked to nature, they encountered suicide bombers among the ants. Bert Holldobler and Edward O. Wilson, in their book Journey to the Ants: A Story of Scientific Exploration, explain that the colony is the unit of meaning in the lives of ants. For the loyal, sterile worker ant, the key issue is the protection of both its queen ant and its worker brothers and reproductive sisters so that they can survive to establish new colonies. In one ant species, worker ants will voluntarily commit suicide to defend their colony, exploding themselves by muscular contraction to spray poison over their enemies. Holldobler and Wilson call destroying enemies by committing suicide in defense of the colony “the ultimate sacrifice in public service” for the ant.

Interesting. The problem with this idea, is that it seems to conflict with the the idea of natural selection'.

http://en.wikipedia.org/wiki/Natural_selection

Natural selection is the process by which individual organisms with favorable traits are more likely to survive and reproduce than those with unfavorable traits. Natural selection works on the whole individual, but only the heritable component of a trait will be passed on to the offspring, with the result that favorable, heritable traits become more common in the next generation. Given enough time, this passive process can result in adaptations and speciation (see evolution).

Isn't 'natural selection' one of the ideas of evolution? As it says 'individual organisms with favorable traits are more likely to survive and reproduce', why then has this kind of ants survived? One possibility is that the specific ant specie which they are in actually thrives better due to this specific kind of ants within them, hence making this specie more survivable. I really don't know, we might as well ask a 'evolution' expert on this one.