On the Road Again: crazy ants and their imposters

Molly Keck, IPM program specialist for Bexar County, was impressed by her first observations of the Rasberry crazy ant in San Antonio. She described her encounter with the ants as cool. Despite thorough treatment with fipronil sprays, there were still lots of activity in the medians and around mulched trees. The commercial property on the west side of San Antonio is the only known location where RCA has been detected in Bexar county. But this site won't be the last; and non-entomologists will not think these ants are cool.

To see Molly and a video clip from WOAI Channel 4 TV about the San Antonio infestation click here

On the road again
Making another leap from its homebase around Harris county (Houston), the RCA has also been officially identified from Jim Hogg county in far south Texas, just north of the Lower Rio Grande Valley. Unconfirmed reports have also been received from several sites scattered from south Texas to the upper Gulf coast. According to Danny McDonald at Texas A&M University, Chambers county, just east of Galveston, also has a confirmed infestation.

If all of this makes you a little nervous (or excited, depending on your perspective), it should. The RCA is not an ant that spreads quickly on its own. Winged forms of the ant are unknown, and the speed of colonization on the ground is relatively slow. But they do appear to be exceptionally good at hitching rides with people. At least that seems to be the only plausible explanation for this rapid spread. Hay bales, potted plants and any soil-containing object that can be picked up and moved is a threat.

Crazy ant imposters
On the other hand, we shouldn't be seeing RCA behind every bush. I just received an ant sample from Hill county this week from someone who thought they might have crazy ants. The ants were fast and erratic-moving and were very abundant. The ants turned out to be a species of pyramid ant (Dorymyrmex sp.), a common native ant that makes little crescent-shaped mounds. Pyramid ants are not known to be structural pests, but can on occasion be extremely abundant outdoors. One client last year sent me pictures of a yard full of pyramid ant nests, complaining he couldn't pick vegetables in his garden without becoming covered with the swarming ants. Unlike crazy ant, which is relatively bristly, and has a ring of hairs around the anal opening at the tip of its abdomen, pyramid ants can be identified by their single node, slit-like anal opening, and raised node at the back end of the thorax (see picture).

Another ant that can be mistaken for crazy ants is the Argentine ant, Linepithema humile. These ants are infamous for their large colonies. They are difficult to control with liquid baits for this reason. Large colonies can drain bottles of baited sugar water within a matter of days. Also, fast moving, Argentine ants are distinguished from crazy ants by their smooth, almost hairless cuticles and by their slit-like anal openings.

If you think you might have crazy ants, and own a microscope, compare the features I've listed above for pyramid and Argentine ants. If, after checking them out, you still think you might have RCA, send your sample to Danny McDonald at the Center for Urban and Structural Entomology.