Iwakuni Marine Corps Air Station officials recently identified two additional varieties of poisonous spiders on the installation that are in the same species as the western black widow, they announced this week.

Brown widow and Red back spiders also have been found in small numbers on the base, officials said. Iwakuni began a battle to eradicate the western black widow spiders from the facility several years ago. Between 2000 and the end of April, pest control personnel found and killed 13,824 of the venomous spiders.

The black widows are not indigenous to Japan; how they achieved a foothold on Iwakuni remains a mystery, although pest control officers have speculated they probably arrived in some type of cargo.

The brown widow and red back spiders were recognized as established in Japan in 1995, according to a base news release issued late Tuesday.

Twenty-seven brown widow spiders have been found on Iwakuni since July 2001, the report adds; however, “they are not considered to be established on this installation.”

One red back spider was found in July 2002; two more were located and killed in recent months. Red back spiders also are not considered established on the base, the report states.

Even though no one on or off the base has been bitten, and none of the poisonous black widow spiders have been found outside the facility’s boundaries, the Japanese government this month is to begin building a 20-inch tall barrier of polycarbonate panels inside the existing security fencing. Designed to keep the spiders on post, the 3,062-yard, $862,790 barrier should be complete by March 15.

Pipe-like traps with chemicals to kill the spiders will be placed along the barrier, about 6 inches above the ground, base officials explained in late April. The barrier will not encircle the base, but is being installed from the fencing starting at the same side of the Monson River as the main gate, continuing to the Northside gate.

“We are making every possible effort, not to just control, but to totally eradicate the spiders,” Capt. Stewart Upton, a base spokesman, said at the time. “In the meantime, if the barrier provides some assurance to local residents, so much the better.”

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