"Mentor" looked like a cross between a dragonfly and a Chinese lantern as it soared toward the ceiling of a Toronto research center, its wings flapping furiously. Below, a bespectacled young man gingerly worked the joystick on a remote control. Mentor started hovering in place, and suddenly the sound of flapping was drowned by thunderous applause.

Mentor's maiden flight last spring marked a milestone in the age-old quest to build ornithopters -- aircraft propelled by flapping wings. Developed by the University of Toronto's Institute for Aerospace Studies and SRI International, a nonprofit research and development corporation in Menlo Park, Calif., Mentor is the world's first hovering ornithopter.

Mentor came into being in response to a vision of a "fly-on-the-wall spy" put forward by James McMichael at the U.S. Defense Advanced Research Projects Agency in 1997. He envisioned stealth "micro-air vehicles" with the size and flying ability of insects deployed to gather intelligence on enemy terrain.

Flapping wings offer several advantages over the fixed wings of today's reconnaissance drones, such as the Predator used by U.S. forces in Afghanistan and Iraq. Flapping wings allow insects and birds to fly at low speeds, hover, make sharp turns and even fly backward.

Flapping produces a vortex -- a tiny tornado -- beneath each wing that creates the push necessary for birds and insects to take to the sky.

But vortices alone do not account for the versatile flight capabilities of birds and insects. Notable among the faculties that flying insects and birds employ is the "clap-fling" mechanism. Like a baritone taking a deep breath before belting out the first note, they draw in air by clapping their wings together, then flinging them apart at high speeds. This creates lift by hurling regions of high pressure below and behind.

Intrigued by McMichael's vision and armed with DARPA funding, James DeLaurier, a professor at the University of Toronto, chose the hummingbird as his model for Mentor for its ability to "hover beautifully" as well as its "smooth, elegant style of switching from hovering to horizontal flight."

With the help of mathematical models created by Roy Kornbluh and his team at SRI International, DeLaurier's team was able to replicate the "clap-fling" mechanism in Mentor. Researchers have been able to build flapping robots that can hover stably and fly horizontally -- though the transition is still very shaky -- with either gas- or battery-powered motors. This and a host of other sophisticated features allow Mentor to remain airborne for as many as 10 minutes -- a record for small-scale ornithopters.

DARPA, pleased with the results of the first phase of research, is now funding more advanced concepts. The program, slated to be funded in 2004, is also backed by a call for proposals by the Pentagon's Army Research Office and the Office of Naval Research. NASA is interested in the possibilities of "bio-inspired flight" for planetary exploration, and held a conference on the topic at its Langley Research Center in Hampton, Va., last month.

When Ephrahim Garcia read about McMichael's "fly-on-the-wall" vision, he, too, figured it was a perfect opportunity to explore ideas he had entertained since he was a young research fellow at the CIA.

"It dawned on me that the key to survival and victory in today's battlefield is information," said Garcia, now a professor of mechanical engineering at Cornell University. He had long toyed with many scenarios, including one in which soldiers would deploy a swarm of camera-equipped robotic insects to probe inaccessible terrain.

While studying insects' flight, Garcia noticed that their wing motion originated in the thorax -- the body of the insect. "Tiny dorsal muscles in the thorax cause [it] to vibrate," said Garcia, and the insect's body amplifies these tiny vibrations to cause large-scale wing motion.

Based on these observations, Garcia, along with his colleague Michael Goldfarb, also set out to design a flying robotic insect. A light metal skeleton formed the thorax while piezoelectric actuators -- materials that bend when electrically activated -- were used to induce vibrations. Using this approach, Garcia and Goldfarb were able to produce the flapping wing motion and 60 percent of the air pressure required to generate lift.

Research into "micro air vehicles" is also afoot at the Canadian Space Agency, a leader in space robotics where researchers have long worked on bio-inspired robots. They developed Canadarm I, the six-jointed robotic arm reminiscent of a human limb, that is in service aboard the international space station, as well as Canadarm II, a mobile robotic vehicle capable of crawling along the body of the space station on its two "hands," end over end, like an inchworm.

Mars exploration has top priority at the CSA, and research and development coordinator Jean-Claude Piedboeuf is once again looking to nature to develop a new generation of planetary probes. He envisions a flock of small, lightweight robots hovering over Martian land rovers and guiding them to places of interest. When it comes to designing small-scale robots, he said, "nature can provide ready-made solutions."

Piedboeuf's team is working on mathematical models of flight conditions on Mars and calculating the optimal wing span for robotic insects capable of flying in the Red Planet's thin atmosphere.

Similar research is underway at NASA's Jet Propulsion Laboratory in Pasadena, Calif. As manager of Bio-engineered Exploratory Systems, Sarita Thakoor is spearheading an effort to develop advanced planetary probes inspired by the insect world because, she says, "centuries of evolution have produced structures and systems that work very well."

The absence of a magnetic field on distant planets would require robotic flyers to rely on their own resources to navigate and achieve flight control -- just like insects. With this in mind, Thakoor and her team have developed and successfully tested autonomous control and navigation systems based on honeybees and dragonflies. Thakoor hopes to see insect-inspired probes in action on a future mission to Mars slated for 2009.

Before miniature flying robots can become more than laboratory toys, however, researchers will have to boost their performance.

Having spent the past decade developing rubbery muscle-like materials that contract and relax when activated electrically, Kornbluh at SRI is now looking to use these artificial muscles to generate wing motion. Meanwhile, DeLaurier is exploring mechanisms that would allow Mentor to shift smoothly from hovering to horizontal flight, just like a hummingbird.

Another major obstacle is that the prototypes consume an enormous amount of energy, Garcia said. Advances in flying robotic insects will have to go hand-in-hand with research into smaller, more efficient engines, he said.

"Imagine this," he exclaimed, "we send this super-sophisticated flying probe to Mars, only to learn that 10 minutes into the operation, it has run out of gas!"