An aggressive species of ant may be losing ground in North America to a more aggressive species, a study said published in PLoS One. The danger for humans is that the on-the-rise Asian needle ants have venomous stings that can cause weeks of burning and itching — and more severe reactions in victims who are allergic. Argentine ants do not pose a direct threat to humans. The researchers think the Asian ants have an advantage over the Argentines because they are active in cool weather, when the Argentine ant rests.

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