TARANTULAS," says Sheila Mutchler, director of Washington's Insect Zoo, "kick off the hair on their backs as as defense mechanism. They'll run into a hole when pursued by a predator, wait till it gets close, and then kick with their hind legs -- the hair gets in the mouth and eyes of the enemy, and stings. This particular tarantula kicked off its hair out of nervousness."

We look down into the Plexiglas case that's the first thing you see when you walk into the zoo (hidden far back in a corner of the Museum of Natural History). A four-inch tarantula with bright orange knees has a two-inch bald spot on its back exactly the color and shape of a baby's powdered cheek.

"And he got nervous because people tapped on his cage. We keep him right up here in front so we can explain how that disturbs the animals. If you're ever tempted to tap on a cage, we hope you'll think of this poor little nervous creature, and never, never do it."

It's hard, at first, having somebody trying to make you feel sorry for a tarantula. In fact, as Ms. Mutchler points out, most people's reactions to the tarantula start as, "Yecccch! Is that thing alive?"

"But it only takes four or five minutes for them to go from revulsion to total fascination. Look at these walking sticks --the world's longest insect . . ."

THE CASE next to the tarantula has a small bush that seems to be covered with dead leaves, hanging down from branches and swaying in the breeze as if they're just about to fall. It takes your eyes a minute, even after you realize that there couldn't be a breeze inside a solid plastic case, to see that they are actually insects, six or seven inches long even in the curled position they get themselves into so that they look -- even from an inch or so away -- exactly like a leaf.

Next to them are the giant millipedes --four or five-inch-long black wormy things with a fringe of legs like a Wimpy moustache. Giant cockroaches that look like seed pods dropped from trees. Eastern Lubber grasshoppers, that start out an inch long, black with gold piping, and gain colors with every moult. So by the time they're three inches they are a big green bug with red sides, gold highlights, and in general a barbaric warrior appearance. One cage is full of monarch butterflies and their cocoons, which are bright green with little golden flecks and hang from the ceiling like jade earrings. Unicorn beetles, as big as your thumb, speckled yellow and black like a shiny stone -- these fearsome and exotic bugs were gathered along the canal in Georgetown. More walking sticks from India, which look not like leaves but like thin green branches -- and are even harder to see than the leafy kind. Indian walking sticks, says Ms. Mutchler, are parthenogenic --able eggs without mating.

THE INSECT ZOO is filling up. Little kids coming in, recoiling at the tarantula cage, then looking on in fascination as the volunteer guides explain to them that tarantulas kick off their hair because they get nervous, and this poor bald tarantula got nervous because . . .

A red Plexiglas cage holds a bunch of ordinary house-variety cockroaches. "We started out with a red cage," says Ms. Munchler, "because we thought that since these are nocturnal creatures, they'd move around more. That didn't work. But we kept the cage, because . . . well, because many people don't like ordinary cockroaches, and if you want to you can pass by this cage without really seeing them. But if you want to look . . ."

A kid with his nose pressed up against the glass, dragging his reluctant mother: "Look at these, these are really little cockroaches, Mom."

"You could have seen lots of them in our old house if you were old enough; let's look at something else," says reluctant Mom.

"But why did you move, then?" asks the kid. "Or else couldn't we of took some? Look at them climb, Mom!"

The mother pulls the kid away and then stops suddenly, absolutely fascinated, in front of case full of sowbugs -- little gray things that curl themselves up into a ball when they feel threatened, or just because they think it's a decorative thing to do.

"Ooooh, look," she says, laughing. "I haven't seen them in years. We used to find them in your granny's cellar. And we called them roly-polys."

One more convert, charmed by the odd little charmers of the Insect Zoo. Mother and son wander over to Cleveland Anderson, a volunteer who is explaining to a small group that these creatures have the scientific name of arthropods. He holds in his hand a giant Madagascar cockroach -- three inches long, thick as two fingers, black head and dark amber body.

"These cockroaches are able to hiss," says Anderson, "and they do it by forcing air through the breathing holes in the side of their bodies." He taps the big bug on its fat little tail and it goes "Ffffffssssss!" loud enough to be heard six feet away.

"Now who wants to hold this beautiful hissing cockroach?"

Out goes the son's hand, and in goes the roach; it covers his whole palm and just sits there quietly. His mother gets ready to take a picture -- then asks Anderson to take a picture of both of them -- each holding a roach. Out comes another giant Madagascar, dropped in the mother's hand, and the picture is taken.

IT SHOULD have been taken with a movie camera, of course, to record the change on the mother's face from determined bravery to stoic calm to delighted giggle.

"It tickles," she says, giving her roach an experimental tap on the tail.

"The hissing cockroaches are everybody's favorite," says Anderson. "They really talk back to you, and you feel that you have a personal relationship with them. The guides are always giving them names -- this is Ophelia, you can tell she's a female because of those two lumps on her carapace. Your mother's got Hamlet. Tap him again."

"Ffffffssssss!" says Hamlet, right on cue. And off go mother and son -- she is laughing and shaking her head "no"; probably I think because the kid is still trying to get her to at least move a couple of those cute little cockroaches into the new house.

Anderson is a student of forestry at the University of the District of Columbia, and has seen all this before.

"I became a guide because it helps a little with the study of forestry -- but really because I just love kids," he says. "The funny thing is, they're absolutely fearless till around eight. You can put anything in their hands. After that, you have to explain things. But you can still get most of them to take the cockroaches. We also hand out tobacco hornworms -- beautiful little blue caterpillars with gold markings; they feel like Play-Doh. Here."

They do feel like Play-Doh.

"Now, millipedes most people think are going to be slimy, because they look like worms. But here."

The millipede I get is about three inches long, dry and not at all slimy, with tickly legs that help it move up and down my hand. By the time I get to hold a hermit crab, who sits in a four-inch conch shell and pokes his head out to watch me watching him, I am starting to enjoy myself. There is something about these outsized bugs -- arthropods, I mean -- that makes you think of a household pet.

IN FACT, across the room is a guy in deep conversation about his pet tarantula.

"This is my second tarantula. I only got it after I got married. The first one -- I think my father gave him a couple shots of Raid, you know? He never did like any of the arthropoda . My wife is different -- she doesn't care that I got snakes, lizards, I got a five-foot Indian tree iguana -- better than the one at the Bronx Zoo, a real beauty."

"No dogs, no cats," sighs the wife, as she has obviously sighed many times before. "Just weird pets."

"The first time my tarantula molted I was scared to death," says the weird-pet owner. "They turn over on their backs, you know, and they have like a trap door they squeeze themselves out of. They leave the whole moult behind, legs and all. And here I am coming into the room where I keep my tarantula in an aquarium.Only all of a sudden, I got two tarantulas. Like this, I'm walking up." He takes a few cautious mock-trembling steps."Because I know it couldn't be Son of Tarantula. Nothing grows that big overnight. And I figure if a new one can get in -- the old one can get out. But it's all hollow -- perfect, though. I kept it around a couple days because it looks exactly like a live tarantula. I think actually that's why my father give it the shot of Raid -- seeing the moult sitting on my bureau and figuring he's gonna have those things all over the house . . ."

A 10-year-old appears with his parents in tow and asks, "You have some tarantulas you don't have out on display?"

A guide explains that there are more than a dozen tarantulas, rotated on display, so people can watch them being fed crickets (which they eat, when and if they feel like eating -- tarantulas can live two years without food).

"Well, then, you got a tarantula named Boris? Because he used to be my brother's until Mom said he was getting too big."

Boris, it turns out, is well-known to the guide and beloved by all. He used to have his own private case but now he is in the big mixed case that dominates one whole wall of the zoo.

"This case . . ." sighs Sheila Mutchler. "It's like a sponge. You know, when this exhibit was designed nobody really knew what would happen. We just did what we thought would work -- and sometimes it didn't. You need lots of insects to fill up this space --and they're all eating each other all the time. We thought we could fill this space with butterflies. Now, butterflies are not the brightest arthropods. We have to put them on their food in the small cases or they won't eat. And everything seems to like to eat butterflies. We'd have dozens when we went home at night -- and then come in and find nothing but their poor little bits of wings all over the ground. Still, Boris seems to like the big case, and the ant lions . . . And we hope we'll discover something. We did with the ants."

THE ANTS are in a small plastic case, with two plaster nests -- one gray and full of ants, one white and empty.

"We started out with those two nests separated by long plastic tracks, and a case in the middle filled with potted chrysanthemums. And in two days all the ants had gone into the pots where you couldn't see them. So we started over with a new batch of ants and cut chrysanthemums in vases of water. And it took about a week for all the ants to fall in and drown. Then we worked out a very expensive case with all sorts of ramps and tunnels for the next batch -- and it kept clouding up with algae so you couldn't see it. Finally, we put cotton in the vases, so the ants couldn't drown, and just stuck everything together -- and it worked. Except that the ants still don't seem to like the white nest."

The ant exhibit is actually the best, though not the prettiest, I've ever seen: These are leaf-cutting ants, and you can see for yourself which are the cutters, the soldiers, the garbage collectors, the queen and the larvae (which look like grains of rice).

In fact, because the Insect Zoo seems to concentrate on what works as an exhibit it's able to keep visitors fascinated -- and incidentally do some teaching. Most everybody leaves knowing something more about arthropods, just as most everybody leaves by revisiting that bald tarantula -- and never, never tapping on his case. Poor little fella.