THE LATEST 3-D IMAX film at the National Museum of Natural History opens with a series of tiny yellow spheres balanced on green leaves. Each is covered in a swirling, symmetrical pattern and, were it not for the leaves, you might think the images were from a coral reef -- or an Easter basket. They pass before you have time to stop and think, "Ewww, gross, bug eggs!"

The film is "Bugs!," and many of its characters appear onscreen at up to 250,000 times their normal size. Characters such as the ant that struggles to drink from a quivering raindrop that's many times larger than it is. The ant leaps on top of the raindrop and bounces, suspended, on its surface like someone jumping belly-first onto a water bed. The large-format feature premiered at the Natural History museum this month. (Nate Erwin, director of the museum's Orkin Insect Zoo, acted as one of its consultants.)

"Bugs!" is more cinematic than many nature films. Director Mike Slee chose the two featured performers based on the dramatic potential inherent in their natures. Hierodula, a praying mantis, is a carnivore who faces decapitation by his mate; while Papilio, a caterpillar, must undergo metamorphosis. (The monikers are derived from the insects' Latin names.) These facts combine to give the story its narrative arc. Indeed, "Bugs!" is a little like a Hollywood thriller in which we meet two characters separately and know they're going to cross paths in a particularly unpleasant way.

The movie was shot on a specially constructed set in Borneo and on a sound stage in Witney, England. Where many nature movies begin with film footage and extrapolate a story line after the fact, "Bugs!" was storyboarded before the filmmakers began to work -- that is, its scene-by-scene action was mapped out. For that reason, much of the filmmaking process consisted of waiting around on the soundstage for the bugs to enact their big scenes. The waiting paid off: The film includes remarkable footage of hundreds of praying mantis babies emerging from an egg sac and of a butterfly's ungainly emergence from its cocoon.

"Bugs!" offers audiences an insect's-eye view of a world, "where raindrops fall like cannonballs and a blade of grass soars like a skyscraper." A praying mantis clings to the underside of a leaf, sheltering from the rain like a pedestrian under an awning. Two multi-horned rhinoceros beetles battle for the favors of a female, looking no less ferocious than their mammalian counterparts. (It's all a matter of scale; for their size, the beetles are among the strongest animals on Earth.) One square mile of land in a tropical rain forest, we learn, holds as many insects as there are people on Earth. More than 40 insects appear on screen; let's hope Warwick Vardy, the film's "Bug Wrangler," got a nice trailer.

The film's often mordantly funny narration was co-written by Slee and Abby Aron. It's read by Dame Judi Dench, whose delivery adds a nice touch of gravitas to the proceedings. "In the rain forest, you're on somebody's menu the moment you hatch," she tells us at one point. Or, at another, "Reproduction is what bugs do best."

Both of the film's principals get star turns. The praying mantis, the movie's heavy, got the biggest audience reaction with his lurid fly-eating scene. He bites off a fly's head -- "these are the best bits, packed with protein," intones Dench -- and the soundtrack fills with crunching noises as he chews, a wing and two legs sticking out of his mouth. The caterpillar, our doomed heroine, does her share of eating, too. If you've ever read Eric Carle's children's book, "The Very Hungry Caterpillar," and thought, "Hey, this would make a great movie!," it's too late. Little Papilio starts by eating her own egg case, and goes on to increase 100 times in size in just a few weeks.

The combination of large-format film and "small-format" subjects is an interesting one. Seen up close, tiny plants and animals, like a rosebud and the aphids that swarm over it, are unrecognizable. And because the film is also in 3-D, the images are not only large, but close. The kids in the audience at a recent showing flinched as a spider descended directly into the frame and batted at the butterflies that seemed to float directly into the audience.

As realistic as such scenes are, sometimes celluloid bugs aren't enough. On Saturday, the museum will host an "Insect Expo," where visitors will have a chance to meet museum entomologists and see live specimens of bugs unusual and commonplace. Bring a magnifying glass -- and watch out for the rhinoceros beetles.

NATIONAL MUSEUM OF NATURAL HISTORY -- Johnson IMAX Theater, 10th Street and Constitution Avenue NW. 202-633-7400. "Bugs!," which is 40 minutes long, screens daily at 10:20, 12:15, 2:10 and 4:05. $7.50, children and seniors $6.

Saturday from 11 to 4 -- "Insect Expo," experts from the National Museum of Natural History and the United States Department of Agriculture's entomology laboratory will be stationed throughout the museum to discuss their research and the museum's insect collections. In addition to mounted specimens, there will be live bugs to see up close in the theater lobby, on the ground level, in the rotunda and, of course, at the Orkin Insect Zoo. These include butterflies, scarab and dung beetles, a Madagascar hissing cockroach and a queen leaf-cutter ant and her colony. Visitors can also sign up for behind-the-scenes tours of the Scanning Electron Microscope Lab and see bugs magnified hundreds of times. Special children's attractions include docents dressed as insects and bug-themed arts and crafts projects.

Hierodula, a praying mantis, preens on a rain forest leaf in the IMAX film "Bugs!," now showing at the National Museum of Natural History.