Q A few days ago, at dusk, my husband and I came upon dozens of ants in one place on the sidewalk, running around in circles. I think this was an ant swarm, which I understand may be related to mating or to finding new nests. About a block later, we came across another ant swarm, and then a block or so later, another one. The next night, we took our usual walk at about the same time and didn't see any of them. I think these were sidewalk ants, but what were they doing? What determines when the ants swarm, and why would we see many on one particular night and then no more?

A You are correct, you were seeing what sounds like pavement ants, but the activity you describe does not sound like a swarm. Ant swarms involve winged males and females. Instead what seems most likely is there were two pavement ant nests very close together and they were fighting with each other. This is more likely during late summer as young nests become larger and come into conflict with neighboring nests.

Jeff Hahn, University of Minnesota Extension

Cleaning shower tiles Q I recently purchased a 30-year-old townhouse with ceramic tile on the shower walls. The tiles are dull and spotted. I've tried Lysol Basin, Tub and Tile cleaner, Soft Scrub and Lime Away. The tiles feel smoother, but the spots remain. Any suggestions?

A It sounds as if the tile was subjected to harsh cleaning methods that may have etched or scratched the surface, making it more susceptible to staining. You can try cleaning the tile again with CLR, a hard water stain remover. Rinse and wipe dry with a terry cloth towel. Then apply a coat of polish from a tile store or an automotive supply store.

If it turns out that the tile is too damaged to be restored, consider a tub surround. Installed directly over the tile, the acrylic or even Corian surface will be watertight. You can do this yourself, if you're handy. Kits are available at home improvement stores. Or contact a tub refinishing company or bathroom contractor.

Send your questions to Fixit in care of the Star Tribune, 425 Portland Av. S., Minneapolis, MN 55488, or call 612-673-7032, or e-mail fixit@startribune.com.