Ant combat
From time to time, you will encounter ants on patrol. These ants seem indestructable at first, but Dr. Platt will eventually tell you how to defeat them.
On the first encounter, you will see a single ant on patrol. You will need to kill it by aiming your shots to hit the antennas; try using the lower leg joints of the ant in order to align your shots, and adjust your aim. If you run out of bullets, you will reload the chamber and wait.
When the ant leaves the left side of the screen, there is a high chance it will make a second attack at point blank. This is your last chance to shoot the antennas before the ant sends you to the hospital. In other cases, the ant will abandon the area and leave; this is treated as a failure to stop the ants.
When the ant is killed, you will be attacked by a swarm of ants; see below.
Ant swarm
After killing a single ant, or entering an area that is under heavy attack, you will be dropped into a combat situation.
Ants will either approach from offscreen, or by crawling out of the ground.
Your grenades are thrown about one ant-length; if you land a direct hit, you will kill a given ant; near-misses may also kill the ant, but they can survive them just as easily. Destroying four ants will repel early columns, but the later and larger ant swarms require more casualties to repel, and in the final swarms, more casualties than you have grenades.
If you run out of grenades, run. If you travel far enough, you will eventually collapse from exhaustion but this is preferable to potentially losing two days by being attacked by an ant.