By the light of day Tom Valega is a grants administrator at the National Institute of Dental Research. But under the shadowy cover of dusk he turns into the "Bat Man of Rockville." (Please, no biting jokes.)

Valega, a "self-taught bat enthusiast," acknowledges that he is "still in the learning stage" about the "grossly misunderstood" creatures. But it doesn't take long to discover that he knows a lot about bats. So listen: Forget those vampire movies. Bats don't suck blood from humans' necks. And bats are not blind. They have tiny little eyes that work just fine, says Valega. But they also have something better: sonar sound, a pitch ranging from 20 to 160 kilohertz, which enables them to find food and shelter in darkness.

The sound is too high for humans to hear, but with a "bat detector" the size of a pocket radio, the Bat Man can tune in to the cacophony of bat chirps and clicks, which enables him to lead small groups of bat fans on hikes. Which brings us to Wednesday night -- Halloween, in case you've forgotten. Valega's Twilight Bat and Owl Hike (more about the owls momentarily) begins at 6 p.m. at the Wild Bird Company in Rockville. It's free, but reservations are a must -- 301-279-0079.

Bats eat up to a third of their weight in insects daily. So, as insects get scarce in the fall, bats start to migrate to their favorite caves to hibernate until spring. This is where the owls come in. If the bat brigade is short on sightings, Valega will don his "Wizard of Owls" hat, play a recording of owl calls on his boombox and wait for a response, which usually comes in just a few minutes. When it does, Valega will scan the trees with a 750,000-candlepower beam and spotlight the owl like a stage star, so there's a show, bats or no.

One other thing: While all this hooting is going on, Valega says the bats are mating elsewhere. The sperm will be dormant until spring, when the female bats will awake pregnant. A woman on a recent bat excursion theorized that the delayed activation of the bat sperm is nature's way around "lazy male bats who sleep longer than females," but you can't prove it by us.