When River House dwellers returned to campus this past week, some found more than the standard- issue desk and bookshelf waiting for them in their rooms.

Cockroach sightings, seemingly concentrated in Eliot and Lowell Houses, have prompted numerous visits to undergraduate rooms by University-employed exterminators and have left some students feeling nervous about these unwanted guests.

Laura P. Humber '02, a resident of Eliot House, said she started screaming when she saw roaches climbing out her drain after turning on the shower.

"They were large and brown," she said. "We threw my roommate's Steve Madden boots at them."

Harvard's bug czar is Gary D. Alpert, who carries the more formal title of Entomology Officer of Environmental Health and Safety.

Alpert says these visitors are standard American cockroaches. They gain access to dorm rooms, he said, in the summer months when shower pipes are dry and the roach can climb up through the drain.

Usually, plumbing systems contain a "water trap," a kind of moat where water collects in a curved pipe. Normally, cockroaches can't cross it, but in the summer months the water evaporates and the roaches can get inside.

When newly arrived students turn on their shower for the first time, they might be greeted by roaches who have made their home in the pipes and are being forced out by the running water.

Alpert says once occupants start taking regular showers, keeping the drain wet, the cockroaches will disappear.