"Somehow the toilet paper roll is on the wrong way again. Just a heads up."
Fortunately, there are a handful of parasites who want nothing more than to ruin an ant's day. The liver fluke (Dicrocoelium dentriticum) in particular spends a healthy portion of its existence trying to get an ant accidentally eaten by a cow. The liver fluke will travel through three different species of animal in its life but will only actively try to kill one of those hosts. It begins as an egg in cow feces which is devoured by a snail. It hatches inside the snail and then gets expelled into a slime ball which is, in turn, eaten by an ant.
This is where the liver fluke gets malicious.
It will infect the ant's mind, changing the insect's behavior -- but only at night. The ant functions normally throughout the day until the temperature drops in the evening, at which point the infected ant feels a very specific urge to climb to the top of a blade of grass where it will potentially be ingested by grazing cattle.