As Gwen Gracia screams, the almost three-inch-long hissing cockroach she is holding is flung to the floor of the Smithsonian's Insect Zoo.

"Oops," says Gwen Gracia, a mite flustered.

The cockroach, quickly and efficiently scooped up by bugkeeper Wendy Shay, doesn't even hiss.Cool, that cockroach.

Gwen Gracia isn't quite as cool. But considering that she is just emerging from some 25 years of a crippling cockroach phobia -- so disabling she couldn't even move into an apartment she'd rented -- the fact that she'd held the hissing cockroach for 15 seconds before dropping it was a victory of no mean proportions.

"My stomach is all knotted up," she said later. "I think now I'm for the ice cream. . ."

The Insect Zoo is part of Gwen Gracia's therapy at Dr. Robert L. DuPont's Montgomery County Phobia Clinic. It's called "contextual therapy," and she's one of his patients who's bugged by bugs.

Because of Halloween, the Insect Zoo people thought it would be a nice idea to invite Dr. DuPont to come (with patient Gracia and therapist Linda Spivak) to talk to their visitors and staff about entomophia, which is what the scientists call really being bugged by bugs.

"Almost everybody," said Dr. DuPont, "has some anxiety about insects. They're creepy crawlies and there is a fear reaction from the unfamiliar. But some people have a tremendous terror reaction and think about insects most of the time."

As Dr. DuPont describes it, and as Gwen Gracia confirms by her own experience, when a phobic person sees a bug, "the realistic thinking goes down and the phobic thinking goes up."

In other words, reality fades away -- the presence or absence of other people, the circumstances, the place -- and "all the person can do is think about the bug; What if it jumps on me? What if it bites me?"

Says DuPont, "Phobia is a disease of whatifs."

Actually, bugkeeping is kind of a job of what-ifs.

What if the tarantula jumps out of its glass case when it is getting it weekly cricket lunch? (Not likely, but it has happened.)

What if the Australian stick bug lays an egg in somebody's pocket and decimates America's rosebushes. (Also not likely. Besides, it probably wouldn't make it through the winter. However, the USDA worries a lot.)

DuPont's desensitizing treatment begins with pictures of the offending critter, progresses to handling the real thing. He comes to the zoo with his patients because, he notes, "When you want a cockroach, of course you can't find one."

Volunteers at the Insect Zoo are quite the other side of the coin from Gwen Gracia. They get off on bugs.

There is, says staffer Jim Bryant, "something we call the Tarantula Club," made up, puts in Wendy Shay quickly, "of an elite corps of volunteers who are trained to pick up tarantulas," the spidery things most people could live without.

On the other hand, it wouldn't be hard to get attached to the Australian stick bug. It looks like a cross between a fat, 4-inch-long scorpion and a dead rose petal. But it has the personality of a Labrador Retriever. Cuddly, but not made for cuddling. Even Gwen Gracia termed it "rather sweet."

Then there's the Hercules Beetle that likes to dive headfirst into a slice of banana.

Then there's the tarantula that . . . pounces . . . on . . . a . . . poor little . . . cricket . . .

Buggy things make up about 80 percent of the earth's population. They breed like, well, like flies.

They could probably take over if they thought about it.

Think about it.