Red ants are not poisonous. Whilst they may be very irratating, and sitting on a red ants nest is far from pleasurable, red ants are not poisonous to humans. Red ants are aggressive and territorial, but to humans no real threat. read more
There is also the Harvester Ant which is sort of like the semi-truck of the red ant variety and some varieties of Harvester Ant (Red w/ black abdomin) can deliver a very painful sting as well. The methods for getting rid of the above ants are the same however. read more