[Annual Ant Control Issue] Odorous House Ants Simplified

Features - Cover Feature: Ant Control Issue

OHAs can present several challenges but patience, persistence and extra effort will lead to success.

April 24, 2015
Scott Robbins
Adult odorous house ant, Tapinoma sessile. Joseph Berger, Bugwood.org

Ants are, by far, our No. 1 residential callback generator. I’m sure this is something we have in common with many other PMPs, regardless of your region. The odorous house ant is the primary culprit in our service area. With multiple queens and nesting sites in a single colony, this ant outcompetes other native species in urban environments1 and proves a very worthy adversary for even the most veteran technician and a recurring irritant for their clients. In the following article, we’ll review some common control techniques as well as tips from the trenches that I hope will make you more successful in managing this, as well as other, tramp ant species.

Seek and Destroy.

The best advice for odorous house ant control has always been to locate and directly treat the nest. If only it were that simple. As previously mentioned, odorous house ant colonies most often have multiple nesting sites. They are transient and opportunistic nesters, utilizing virtually any natural or manmade void. Locating all of them is a time-consuming task. Nests can be under mulch, landscape stones, piles of leaves, pine thatch or grass clippings. Our yards are full of extruded plastic voids like the children’s sand box or swing set, the mailbox, gutter downspout splash pans or the pad under the HVAC unit. In some situations, nesting sites may not be accessible for treatment, as when ants are trailing from a neighboring property. Another issue may be a lack of activity due to weather, such as rain or temperature extremes like a hot surface under the July sun or cold temperatures. While you could inspect some likely nesting sites and apply a residual product to exterior entry points (weather permitting) or make some bait placements in the interior problem area, a better option may be to return when the weather is more favorable.

What everyone always wants to know with most pest species is “what is the most effective product to use (a.k.a. the magic wand)?” While some materials have certain benefits over others, it is important to weigh the strengths and weaknesses of your selection and match it to the needs of your client and the target application sites. For instance, non-repellents work extremely well when odorous house ants are trailing and foraging heavily. However, some are limited by number of applications per year, application site and/or speed of control. A better choice for knockdown when the customer wants immediate relief might be one of the dual active products. These may not be a viable option depending on application site and timing regarding pollinator activity in the area. I think the prepared PMP will have at least one of each of these residual products at the ready.

I have technicians come to me who have “tried everything.” They’ve applied this product and that product and still another around the foundation to no avail. It is usually not a question of which product was applied, but WHERE they were applied. (It might also be how the product was mixed.) I can grab a long screwdriver and a can of Ortho from under the kitchen sink at my mother-in-law’s house, go out in the yard for an hour or so locating nests and treating entry points and effectively manage her odorous house ant problem for a few months. The difference between me and the technician is I have time to kill (pun intended) while the technician is up against scheduled stops and production demands. However, it must be considered how much more satisfied our clients might be if we had invested the time up front to resolve the issue rather than expend it on repeat callbacks or follow-up services (plus more fuel and our customer’s patience). The bottom line: 15 minutes is not enough time to solve a serious odorous house ant problem.

Leave No Stone Unturned.

Something else must be considered. What if the ants are not originating from outside the structure? The technician may literally have left no stone unturned and turned up nothing to alleviate the activity inside the home. Many times I have placed a granular bait on the ground and watched them carry it into, rather than away from, the structure. I have noticed many of our problem odorous house ant accounts have brick veneer. The veneer has multiple entry points through weep holes as well as potential cracks in the mortar and provides a permanent void and travel corridor around the structure that makes direct nest treatment impossible. Nests also can be located in crawlspaces behind insulation or under vapor barriers. I’ve even seen a few under carpet in the living space and one nest inside a clock radio.

What if you’ve looked everywhere inside and out, used every liquid residual imaginable and still have ants? Time to let the ants kill themselves. (Yes, they will do it if you and the homeowner will let them.) How many ant baits and formulations do you have at your disposal? Many of my technicians have a ‘go to’ bait and usually that is a user friendly gel that fits neatly into their cargo pocket or service kit. What if those ants at that particular client are not attracted to that bait because of the nutritional needs of their colony at that time? A bait only works if the ants consume it, right? Best to carry an alternative to ensure feeding. It is sometimes difficult to find enough cracks and crevices to place one bait, let alone two. How many ants will a 3-gram placement in a gap under the kitchen window kill? I like to utilize bait containers in indoor foraging locations to hold more bait without the mess. It is important to communicate to your customer that those ants must be left undisturbed to feed and distribute that bait back to their nest mates. It is also important to set your customers’ expectations when using slower acting non-repellent products that they may see activity for a few more days after treatment. A best practice is to set a follow-up, in person if the activity was severe or the customer was particularly unhappy or distressed. At a minimum, a phone call the next week to ensure your treatment was successful goes a long way.

Adult odorous house ant, Tapinoma sessile.

Truth be told, while I do enjoy uncovering and eliminating odorous house ants directly, I utilize larger quantities of bait than most of my technicians when troubleshooting. While this makes some managers cringe when considering product costs, it is much less than lost production time or a cancellation. What about outdoor placements of gels? Are there more cost-effective bait alternatives available? Granular or liquid baits may be such an alternative. Large amounts of these products can be placed in any one of many outdoor ant stations available. I find a combination of bait formulations in multiple placements and targeted applications of a properly labeled non-repellent or dual active residual to nesting sites, along trails and entry points work best.

Establish Expectations.

Now that we’ve eliminated the odorous house ants, there is one more issue to communicate to your client. More than likely, they will be back. While your best efforts may have wiped out all of the ants in their yard, the same harborages, food sources and other conducive conditions that allowed them to proliferate still exist. Nature abhors a vacuum and the ant colony next door will not pass up the opportunity to expand its territory next year. If you communicate this expectation to your customers in advance, they should be must less irritated if and when it happens. Happy hunting!


The author, an associate certified entomologist (A.C.E.), is technical director of Evansville, Ind.-based Action Pest Control, and can be contacted at srobbins@giemedia.com. Action Pest Control is a division of Scotts LawnService.


1Salyer A., Bennett G.W., and Buczkowski G. 2014. Odorous house ants (Tapinoma sessile) as back-seat drivers of localized ant decline in urban habitats. PLoS ONE 9(12):e113878