MISSISSIPPI STATE -- Old railroad crossties are basic elements in many landscapes, but in some cases they are helping spread the Formosan termite.

Formosan termites are a subterranean species that require moist environments to live. They are a tropical species from the Far East which tunnel from location to location to prevent them from drying out when exposed to above-ground conditions.

Formosan termites have caused tremendous problems in New Orleans. Infestations can be found in the Coast counties of Jackson, Harrison and Hancock, as well as further north in Lamar, Forrest, Jones, Rankin, Madison and Lauderdale counties.

Some evidence suggests areas in Mississippi south of a line from West Point to Cleveland can support Formosan termites. The southern third of the state remains the primary area of concern.

James Jarratt, entomologist with Mississippi State University's Extension Service, said crossties have been found to be responsible for several of the Formosan termite infestations found away from the Coast.

"Evidence indicates Formosan termites are being moved fairly long distances in crossties," Jarratt said.

About 10 or 15 years ago, several small railroad lines in the southern United States were abandoned. Some of the crossties on these railroads in south Mississippi and Louisiana were infested with Formosan termites. People salvaged the rails and the crossties, and the Formosans began to spread as the crossties were sold.

Crossties are a popular landscape feature used to edge gardens, make raised beds and more. Crossties are treated with creosote to give them a long life, but in time it becomes less concentrated and termites can enter the wood as it cracks. Gardeners like the weathered look of old crossties and the fact that the creosote is no longer toxic to plants.

If the crosstie contains worker, soldier and reproductive termites, the group can establish a colony where ever the crosstie ends up.

"Be careful when you buy crossties," Jarratt said. "Inspect them to see if they are infested with termites and find out where the crossties came from."

To inspect crossties for termites, separate the bundles and look for evidence of termites between the crossties. Check for live termites, tunnels and soil that has been carried into the wood. Drop one end of the crosstie and examine what falls out.

"Don't buy the crossties if you see termites," Jarratt said.

Examine crossties already in yards and look for evidence of termites. Have a professional identify any termites found. A termite's species cannot be determined from the workers, so look for the winged form or a soldier with its enlarged head and noticeable mandibles.

"Nine times out of 10, if there are termites in the crossties, I wouldn't do anything about them unless the crossties actually touch the foundation of the house," Jarratt said. "Where they touch the foundation, I would at least move them back. If the termites are Formosans and the house is under a treatment contract, then continue on with whatever service you're using."

Jarratt said Formosans are different from Mississippi's native subterranean termites, the eastern termite, in that they form much larger colonies and they build what is known as a carton when they get in buildings. This carton protects the termites and serves as a place where moisture accumulates, eliminating the need for termites to go back outside as often.

Formosans are treated similarly to other subterranean termites, although the carton must be found and removed to rid a building of termites. Jarratt recommended using a non-repellant liquid insecticide on this species.

"Termites are not repelled by treated soil, so they enter the area and the insecticide affects the colony in different ways," Jarratt said. "If the material just repels them away from the treated area, then you have not put any pressure on the termites. They're still there and as healthy as they were. They'll continue to move around and feed and may find a way into the house."