Michael C. LaBarbera is the author of a fascinating article on The Biology of B-Movie Monsters
, which contains the following useful advice:
Here's the trick to defeating the giant ants. You don't want a rifle, you want a pile of bricks and a good pitching arm. One well-hurled brick hitting a leg and--plink!--the leg goes into local buckling and collapses, increasing the load on the remaining legs. Two more bricks and you've taken out all the legs on one side; all the bug can do is scrabble in circles. Three more bricks and the giant insect is completely immobilized.