We have two types of ants in the Northwest which we classify as ‘moisture ants.’  Each of these ants belongs to a different ant genus which may have one or more species which look similar and / or act in a similar manner.  Ants of the genus Lasius, sometimes referred to as cornfield ants, and ants of the genus Acanthomyops, sometimes referred to as the larger yellow ant.  These ants have a few things in common, but mainly, their penchant for nesting in wet decaying wood.

While other ants will nest in wood, wet wood, and even wet decaying wood.  Somehow these two different types of ants got bundled together because they are both fairly small and when they infest buildings they often infest the same areas.

Both of these ants commonly infest trees, stumps, fence posts, and any other wood in constant direct or close contact with the soil.  Soil holds moisture and these ants will not typically infest wood which does not have high moisture content, although on rare occasions they have been known to bring moisture to wood—a process known as ‘farming.’

Other materials besides soil will hold moisture, contribute to wood rot, and provide nesting incentives to these ants.  Beauty bark, wood chips, leaf and other plant debris, sand and gravel all hold moisture very well.  Additionally, many common construction materials exposed to moisture and in contact with wood will lead to moisture problems and ant infestations.

While these ants are often noted around the exterior of the home where siding, or other wood of the structure meets the soil, they can also be found under homes where wood of the structure meets the soil of the sub area, where wood left over from the building process was left by the builder, or where tree stumps or tree root systems where not completely removed prior to building.

On rare occasions, nests of these ants can occur under the concrete floor in basements or in other types of slab homes.  Workers and even the winged swarmers will sometimes come up around the edges of the slab along the interior perimeter of the home, especially if the builder did not clear the wooden form boards used to frame the foundation prior to pouring the concrete which became the slab floor.

These ants can also be found in nests occurring much higher in a building, around windows that sweat, gutters that leak, pin hole leaks in plumbing lines, leaky bathrooms shower enclosures, faulty roof flashing, and even under roofing materials if moisture is consistently present.

Just like Carpenter ants, mature nests of Moisture ants will produce winger reproductives after their nests are well established.  Swarms, or ‘mating flights,’ typically occur in late summer around August.

The most important control aspect for moisture ants is an inspection by a qualified pest control professional.  They should be able to help you pinpoint moisture causes and outline possible steps to reduce the moisture to levels that are no longer attractive to these ants.

A treatment may be recommended, especially if there are a lot of ants, if it will take a little while before all contributing moisture problems can be addressed, in those situations where it just is not economically feasible to eliminate all the moisture problems, or where consumers have a concern about future rot problems.

These ants can and often do tunnel and forage below ground on subterranean insects and insect secretions.  A perimeter band treatment of your structure may not have any effect on these ants; it may not control them or prevent them from nesting, concerns about these ants should be discussed with your pest control provider.

It is important to note that in many areas where these insects are found, rot is found as well. Too often when contractors perform repair work to replace wood damaged by rot fungus and moisture ant infestations they do not remove and replace enough wood.  Rot damaged wood is often cut out at the point where wood is discolored or obviously soft.  Workers often attach new replacement wood right up against rot damaged wood. 

Rot extends inside the wood several feet beyond the point where it is visibly soft or discolored.  It is still there, a living organism, and if there is any future moisture in the repair area it will continue to grow and cause damage. 

While using chemically treated rot resistant wood may slow the spread of rot in an area of repair, it has been our experience that few, if any, contractors are installing these replacement materials properly.  According to the manufacturers, end-cut solution should be applied at every fresh cut, at every crack or split, and at every nail or screw attachment.  Additionally, any chemically treated replacement material specifically used for rot repair in any area of possible future moisture should be rated for direct ground contact.  Too many contractors use replacement materials that are more suitable for decking than for rot repair. 

Treatment of all wood in the area of repair with a material such as Tim-bor will help to prevent the future spread of rot, will help kill moisture ants, and is strongly recommended.  Tim-bor, Bora-care, and other preparations containing borate based fungicides can provide long term control and Tim-bor in particular, as a naturally occurring inorganic mineral compound should be considered a very green approach to rot and insect control.