Episode 6 of "MacGyver"
s01e06 Trumbo's World

Opening gambit - Whitewater Rafting: In the Pyrenees Mountains, MacGyver rescues a prisoner, then makes a daring escape with her by raft. MacGyver comes along on a expedition to Brazil with his friend, entomolgist Dr. Alden. They meet with a landowner and recluse, Trumbo, who is initially hostile. However, when they realize that a mile-wide column of army ants is moving through the jungle, they team together to mount a defense. Alden is killed by the ants, which seem unstoppable. MacGyver tries to flood the ants by filling the surrounding troughs with water, but when that plan fails, he uses a flamethrower to burn the oncoming ants. Out of gasoline and quickly running out of time, MacGyver must come up with a plan to dispose of the ants, or Trumbo will lose in one afternoon what he spent his life assembling...