Factual error: The crew gasses out the ant hill by dropping chemical grenades into the hole. But there are two reality mistakes about the grenades: 1) chemical grenades do not explode; they spray their contents into the area; and 2) considering the size of the ants, the size of their nest must be gigantic, and therefore, it would take more than a hundred grenades to flood it completely with cyanide gas.
Factual error: Grandpa Johnson's .30-30 Winchester rifle was apparently bent by the giant ants during their attack on his store. But as we can see later, the ants' mandibles are too thin and too curved to provide enough gripping and leverage area for bending a metal rifle barrel that severely.
Continuity mistake: When they go to visit the trailer, Pat is surprised by an ant on a bluff. When they shoot it, it falls with it's head just over the edge and two bushes in front of it. They switch to a camera angle from behind the ant and now its head is further back and there is a large white rock in front of the ant's head.
Factual error: In order to keep the giant ants inside the New Mexico nest, the protagonists bombard the entrance hole with phosphorus shells. Phosphorus burns at an average temperature of 5,000° Farenheit. At this temperature, the heat from the shells should have fused the sand around the entrance hole to glass (the threshold for this process is about 4,200° Farenheit), yet the sand remains unchanged.