At the National Pest Management Association's PestWorld 2005 conference in Nashville, Tenn., urban entomologist and structural pest management industry consultant Jeffrey Tucker gave an interesting presentation titled Ants: The Familiar and The Unexpected. One of Tucker's main points involved drawing a distinction between introduced pest ant species — those that hitchhike or otherwise make their way into regions not previously inhabited by them — vs. emerging pest ant species — those that have occupied particular regions for many years without exhibiting invasive behavior until, at some point, they start showing up indoors.
I would like to revisit this subject because of its growing importance to the structural pest management industry, and update the list of ant species that have manifested themselves in the introduced pest and emerging pest camps. The table below provides a thumbnail sketch of how some of the structurally invasive ants sort out into these camps. Notice that certain genera, such as Brachymyrmex (rover ants), are represented by both introduced pest species (such as B. patagonicus) and emerging pest species (such as B. dipilis).
Species
Origin and Year Introduced
Current Distribution in Continental U.S.
Pavement ant (Tetramorium caespitum)
Europe, 1700s
U.S. and Canada
Pharaoh ant (Monomorium pharaonis)
Africa, 1700s
U.S. and Canada
Argentine ant (Linepithema humile)
Brazil, 1890s
Southern half of U.S., except for parts of Southwest; occasional colonies in Pacific Northwest, Midwest and East
Red imported fire ant (Solenopsis invicta)
South America, 1930s
South, Southwest
Caribbean crazy ant (Paratrechina pubens)
West Indian Islands, 1953
Florida
Crazy Rasberry ant (Paratrechina sp. nr. pubens)
?
Texas
White-footed ant (Technomyrmex albipes)
Indonesia, 1986
Florida; occasional indoor colonies in other states
Ghost ant (Tapinoma melanocephalum)
Africa or Asia (tropics), 1988
South; occasional indoor colonies in other regions as well as in Canada
Rover ant species (Brachymyrmex patagonicus)
Argentina(?), 1970s
Southeast (and Texas?)
Rover ant species (B. obscurior)
South America, 1990s(?)
Southern California
Rover ant species (B. depilis)
Emerging (Endemic)
Southwest
Asian/Chinese needle ant (Pachycondyla chinensis)
China, 1930s
Southeast
Odorous house ant (Tapinoma sessile)
Emerging (Endemic)
North America (not yet invasive in all regions)
Thief ant (Solenopsis molesta)
Emerging (Endemic)
U.S. (not yet invasive in all regions)
Small/False honey ant (Prenolepis imparis)
Emerging (Endemic)
U.S. and Canada (not yet invasive in all regions)
So, how is it that regional colonies of odorous house ants, small honey ants, rover ants, thief ants and others can remain structurally non-invasive for many years, and then alter their behavior to commence foraging and nesting in human structures? Take, for example, the odorous house ant. It has been well established as a structural pest in the South for decades, but it did not come to the attention of pest management professionals (PMPs) in Ohio until the 1990s.
Asian needle ant worker
(Photo: Jason Widlacki)
Caribbean crazy ant (Photo: F.J. Santana)
Is it simply an opportunistic response to the presence of quality nutritional resources and favorable nesting conditions? Does the inclination to enter structures get passed down genetically to successive generations?
These and other questions beg for answers that likely will be forthcoming from entomologists and graduate students who study ant behavior and genetics. In the meantime, we PMPs will continue to be mystified by these amazing little adversaries.
