A single spark can start a prairie fire is a classic idiom, which means that a small flame can also cause a raging fire. It means that a small action or strength can also cause a huge impact.
This idiom comes from a fable in Zhuangzi: A group of ants wants to build a house, but they don't have enough strength. They can only work and look for food. One of the ants saw that the other ants were busy and said,"Although you are small, as long as you have the power of a hair, you can start a fire and burn the whole house down." The other ants listened to the ant's suggestion and began to build their own houses. In the end, all the ants built their own houses, but only one ant's house was burned down. The other ants all passed their time smoothly.
This story tells us that a small action and strength can have a huge impact, just like how an ant's small suggestion can start a big fire and burn the whole house down. Therefore, the idiom " A single spark can start a prairie fire " is often used to describe how a small action or force can cause serious consequences.