[Akademee]

Ants won't be attracted to places with no food, did you box have any frames with honey in it? If you did, they love that stuff! You can use things like Diatomaceous Earth sprinkled around or cinnamon, but both have to be frequently replaced, especially if it rains. Your other option is ant moats, where you put each leg of a hive stand in a pan of water or oil and the ants can't cross it.

 

[JWPalmer]

Sounds like the swarm never actually moved in. Yet. You probably saw heavy scouting if it was a swarm trap you set. If you put a swarm in a box, they did not like what you had to offer vs the location they had selected and moved on. Same if you placed a swarm trap near an existing swarm, they may have shown some interest but if the swarm is gone and they are not in your box, you lost them.

The above advice holds true, never have any food source in a swarm trap, including frames with pollen, or ants and roaches will be all you catch.