Question: I have been seeing little ants in my bathroom.  They were in my bathroom this time of year last year too.  There are tons of them & I don”t know where they are coming from and why they are there.  They are only in my upstairs bathroom.  How can I get rid of them?  I live in Hanover, MN,

Thank you!

ANSWER  Probably what you have is one of the carpenter ant species (Genus: Camponotus).  There are several species of carpenter ants across the U.S.  Most are large black ants, but some are red and some are red and black.  Most of the species produce swarms (winged males and female ants) in the spring.  These ants feed on other insects and honeydew from aphids on plants and trees.

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Carpenter ants nest in moisture damaged wood, but do not eat the wood.  If there is a carpenter ant nest associated with the house, it is because there is probably moisture-damaged wood somewhere.  It may be in the bathroom where the tub or shower are not draining properly (or have overflowed and wet the wood), or a porch that is holding moisture, a roof leak, a door frame that gets wet from rain, a downspout or gutter that is not working.

 These ants are usually active indoors in the early spring.  They may be found in the kitchen and some other parts of the house in February and March.  This is usually an indication that there is a nest in the house.  In late spring these ants will move outside and not forage of food indoors again, and this may give the false indication that control have been achieved.

 When carpenter ants are found in the house in late spring it is usually an indication that the nest is outdoors and they are simply foraging for food indoors until there are insects and aphids to feed on outside.

 The best control for carpenter ants is to locate the nest.  A thorough inspection of the house for moisture damaged wood is necessary.  Correcting the problem is the first step, in the process the ant nest can be removed or sprayed.

 Baits are best when the nest can not be located; liquid baits are preferred by ants, but most baits will work if you locate them near the trail of foraging ants.  Baiting takes time, but it will get to the queen in the colony and that is best approach.  Killing the worker ants with sprays is not effective.