If the season is spring or summer there will be a chance fire ants may appear in your sim’s lawns. Every 4 sim hours a test is run with a 1% chance of creating an ant mount at a random spot outside. That doesn’t sound like much, but over the course of a week the chance builds to around 1/3. Sims are practically guaranteed to see at least one fire ant infestation before spring or summer is over, possibly more. Sometimes it’s in the open, sometimes it might be hard to see near outdoor furniture or plants. After around half a sim day, an ant mound will get larger in size and have the ability to create new ant mounds nearby every 17 hours. At first you might see 1 or 2 mounds, maybe even three. Soon, however, exponential growth occurs and those ants can take over an entire lot! (and they might become so many in number the game might get really slow.) Be careful, sims can get bitten if carelessly stepping too close!
Sims walking by may discover and approach the ant mounds on their own. Most sims will get angry but some depending on their interests in science or nature will find inspiration from the little creatures.