The exotic species of ant known as Paratrechina longicornus, or the crazy ant, named for its speedy and erratic behavior when excited, somehow managed to kill off all the other ants over the years, as well as the crickets and grasshoppers.

Swarms of them crawled over everything in sight: thick foliage, damp pathways littered with dead leaves and even a bearded ecologist in the humid rain forest of Biosphere 2, an eight-story, glass-and-steel world in the wilds of the Sonora Desert that cost $200 million to build.

''These little guys pretty much run the food web,'' Dr. Tony Burgess, the ecologist, said as he tapped a dark frond, sending dozens of the ants into a frenzy. ''Until we understand the ecology, we're reluctant to eliminate them.''

Columbia University, an icon of the Ivy League, is struggling to turn a utopian failure into a scientific triumph.

The university took over management of Biosphere 2 in January and is starting to reveal just how badly things went awry when four men, four women and 4,000 species of plants and animals were sealed inside this giant terrarium for a two-year experiment that ended in 1993.

The would-be Eden became a nightmare, its atmosphere gone sour, its sea acidic, its crops failing, and many of its species dying off. Among the survivors are crazy ants, millions of them.

Rather than aiming to recreate paradise, Columbia is now working to make and sustain its opposite -- a kind of atmospheric hell that threatens to choke the globe late next century with high temperatures and high levels of carbon dioxide, a principal agent of global warming. Some organisms in the experiment are expected to thrive, and others to die.

To that end, Columbia is now clearing out old growths and animals, planning new ones and beginning to subdivide the would-be paradise into experimental plots, curious to see if the three acres of futuristic domes here can serve as a scientific testbed for anticipating the effects of a warming climate, and perhaps avoiding negative ones.

Over five years, the bill for the retooling is expected to reach about $40 million, for science and educational programs as well as new construction.

''It's a challenge,'' Dr. William C. Harris, the new president of Biosphere 2, said of the transformation as he sat in his office, with the Santa Catalina Mountains visible out his window. ''This facility was not designed for these kind of experiments.''

Most ecologic research is done outdoors, he noted, and no one has ever before tried to bring it inside on so vast a scale, replete with experimental controls and all the rigor that modern science can muster.

''You can think about doing experiments like you might do in chemistry or physics, where you change things, where you stress the system and see how it responds,'' said Dr. Harris, a physical chemist by training and most recently an official of the National Science Foundation, the Government's main agency for financing basic research.

''The potential is so significant that -- if we can turn this into an experimental tool -- it will resolve questions that cannot be answered otherwise. It will influence how we think about the rest of the world.''

Trucks and construction crews now swarm over the desert site as Columbia nears a milestone in its takeover. On Nov. 25, the Biosphere will open to the public for the first time, at least part of it.

The old habitation area of the Biospherians, as the eight men and women called themselves, has been sealed off from the rest of the domes and transformed into a visitor center full of exhibits on climatic change. It is the first of the subdivisions.

Inside, visitors can learn not only about how the planet is warming but can tour old Biospherian residences and learn something of the glass ark's woes, of how the crew lost weight, got sick and began to grow paranoid about food theft.

''One thing I like about Columbia is that they're getting the history out,'' said Gilbert LaRoque, a Biosphere guide who started working here in 1991, when the first human crew was sealed inside. ''We watched one Biospherian drop in weight from 260 to 150 pounds.''