Pavement ant gets a new name

Tetramorium immigrans nest. Photo by Alex Wild.

A few years ago I was called to a home in the Dallas area to look at a stubborn "fire ant" problem.  Indeed the numerous mounds did look much like fire ant mounds, and the red ants like fire ants; but closer inspection showed the ants to be pavement ants. 

The name "pavement ant" comes from its preference for nesting in open, well-drained gravelly soil typical of sites under sidewalks and other pavement. By building roads and laying concrete throughout our cities it seems we have created the perfect habitat for these ants. 

Temperate climates, like those of the Northern and Midwestern states, are especially favorable to  pavement ants.  In some states, pavement ants are the most common household ant, foraging for crumbs and swarming indoors like termites or carpenter ants. Though less common in Texas, I suspect pavement ants are more common than we realize, often being mistaken for fire ants. 

According to BugGuide.net, there are seven native and introduced species of Tetramorium in the U.S. and 455 species worldwide. By far the most common and widespread species has, until recently, been referred to as Tetramorium caespitum or, more mysteriously, "Tetramorium species E".  This is the only Tetramorium that is a common urban nuisance pest.

It's not common to have an important pest insect whose identity remains a mystery for almost 100 years since it was first recorded. It turns out that the genus to which pavements ants belong is a real "brier patch" of related and difficult-to-tell-apart species. Taxonomists who have studied the group have realized as much and out of frustration have been calling our pest pavement ant "species E" within the T. caespitum "brier patch".  That has now changed. 

Two recent papers clarified the identity of these common ants, and they required some ingenious sleuthing to do it. A paper by Herbert Wagner and colleagues used a combination of two kinds of DNA, numerous body features and ecological observations to untangle the briers obscuring the Tetramorium species in Europe.  When they finished they (in a very scientific way) said "Phew!" and noted that it took six types of analysis to solve the "highly intricate" problem of identifying the European Tetramorium.  Without both molecular (DNA) studies and studying the morphological features of the ants, they never would have solved the puzzle. 

The new name of the American pest pavement ant is Tetramorium immigrans, an appropriate name since our pest turns out to be an immigrant from Europe.  Very similar in appearance to the Tetramorium caespitum first described and named by Carl Linnaeus in 1758, a group of researchers based in Florida and led by Yuanmeng Zhang recently studied the genetics of Tetramorium immigrans populations in the U.S. In Zhang's study, molecular evidence was taken from 90 samples collected across the country by mostly school children using Pecan Sandies® cookie crumbs to attract the ants.  The lack of genetic diversity among all the samples collected suggests strongly that all of today's ants came from a one-time introduction, perhaps as long as 200 years ago. 

What's in a Name?

Why is knowing the name of an insect important? Because IPM is important.  Integrated pest management is the definition of modern, effective pest control. One of the key principles of IPM is that control methods should be based on knowledge of the biology and behavior of the pest.  Without knowing what pest you are facing, its impossible to know with any certainty the lives and behaviors (and weaknesses) of any pest.  

Knowing the right species of ant will also help in selecting an appropriate bait. In the case of pavement ants, the Advion® Fire Ant Bait has a label that includes pavement ant. In the case of the Dallas home with fire ants, Advion® performed well against that infestation. 

Recognizing Pavement Ants

Pavement ant. Note the two node segments between thorax and gaster, two
small spines toward the end of the thorax, and parallel grooves on
the head and body.  Color ranges from light brown to black. From the
Ant Identification Guide by Bayer Environmental Science.   

So how do you recognize pavement ants? Determining Tetramorium ants to an exact species can be a challenge and requires a very fine microscope.  Fortunately, the genus is not hard to identify with a hand lens or modest microscope.  And most Tetramorium found in urban settings and as indoor pests in the U.S. will be T. immigrans.  

Pavement ants are in the ant subfamily Myrmycinae.  Like all myrmycines, pavement ants have stingers (rarely used) and two small nodes (bumps) between the thorax and gaster (tail segment). In addition, look for two small spines on the last segment of the thorax.  Color may range from light brown to black, and all the workers from a given nest will be the same size (monomorphic).  Pavement ants may superficially look like fire ants but they are generally slower, less aggressive when their mound is disturbed, and do not sting. 

Knowing what kind of ant, or any insect, you have in hand is essential to everything we do in pest control.  And having taxonomists working behind the scenes to figure out what pests we have is a real benefit to our industry.

A large scale problem

This wax scale-infested holly could be the
key to controlling ants around your customer's
home.

Ask most PMPs who specialize in structural pest control what they know about scale insects, and you'll get a blank stare. Pest management techs are typically taught little about insect pests of plants, especially tiny, non-descript pests that are frequently well-camouflaged from all but the most highly trained observers.

This is a mistake. A well-trained commercial or residential pest control PMP needs to know about plant pests, especially scales and their cousins the aphids, whiteflies and mealybugs. The key reason is that scales are part of the ecosystem surrounding the home or business, and can play an important role in insect life coming indoors...especially when it comes to ants.

You know ants. Only one of the most important pest issues for the industry around the world. The vast majority of indoor pest ants are sugar-loving.  But these ants don't get their sweet tooth from sheer gluttony (like us!); ants have evolved with a heavy reliance on sugary foods in the form of honeydew.

Honeydew is the sweet excretion product of many plant feeding insects, including scales, aphids, mealybugs, whiteflies and others. Most of us have experienced honeydew when parking a vehicle under a tree during the summer months. Those sticky drops all over the windshield were honeydew, or less delicately, insect poop.

Much like our obsession with sugar, ants have an interesting relationship with honeydew producing insects. It turns out that ants have been relying on the scale insects for so long that both scale and ant have become co-dependent. The ant gets a free, long-term, stationary food source. The scales benefit from the ants keeping down excess honeydew and mold on the old leaf, and even get protection from predators like lady beetles and parasitic wasps.

Ants that naturally feed on honeydew include carpenter ants, crazy ants, odorous house ant, Argentine ants, acrobat ants, rover ants and fire ants...and probably several others I'm forgetting at the moment.  If you're battling any of these critters on a regular basis, you might need to know something about why ants are attracted to your accounts in the first place.  In many cases it probably has something to do with the presence of scale insects around the building perimeter.

Sticky, shiny leaves are one tip-off that scale-like insects may
be feeding on your customers' plants.  Also look for waxy crusts
often associated with aphids, scales and mealybugs.  Honeydew
also serves to grow a black mold called "black sooty mold",
another unsightly clue to a problem.

A few years ago when industry giant (at the time) American Cyanamid was searching for an improved bait for carpenter ant control they turned to experts in insect honeydew for insight. Researchers found that mimicking some of the natural constituents of insect honeydew in an artificial bait was a good strategy for designing a more effective bait.

I'm not suggesting that all ants are attracted to your accounts just because of sugar-pooping pests, but I guarantee you that, when present, these insects will contribute to an ant problem. So what can be done? First of all, learn the signs of honeydew producing insects, and how to select some of the excellent control products on the market.

There's a lot to learn about scale insects--more than I can cover here; but if you're interested in learning a little more, check out this link to a PowerPoint presentation I'll be giving this week on the subject.  The topic is scale insects and their control. I hope the pictures and notes will give you an interesting introduction to the subject and a taste to learn more.  Speaking of taste, I think I hear a KitKat bar calling my name.