Bela Demeter poses for a portrait at the National Gallery of Art. Demeter is a docent at the museum and gives tours that focus on reptiles in art. He had worked for 35 years at the Smithsonian National Zoological Park. (Matt McClain/FOR THE WASHINGTON POST)

In most ways, Bela Demeter fits right in with the other docents at the National Gallery of Art. He wears a sport coat and tie and carries his support materials in a tidy black binder. The giveaway is his long, straight, silver ponytail.

Demeter is a snake person. And that’s putting it mildly.

For more than 35 years, Demeter helped run the National Zoo’s Reptile House. Now his expertise in biology has created an unusual new niche at the National Gallery. His occasional “Dragon Tour” is a witty meander through the museum — covering everything from Leonardo da Vinci’s advice on how to draw dragons to scientific speculation that frogs generate spontaneously from mud.

Demeter meant to leave reptiles behind when he retired: Why volunteer doing the same thing you were once paid to do? His dream was to become an art detective like the hero of Jonathan Harr’s “The Lost Painting,” a nonfiction thriller about the search for a Renaissance masterpiece. The only hitch was that he knew next to nothing about art. Although he considered going back to school, the gallery’s free docent program seemed like a better way to learn.

During the yearlong training curriculum for docents, Demeter not only picked up an entirely new field of knowledge but also found people to share it with. “My wife says to me, ‘Bela, [becoming a docent] was such a good idea. I’m not enough of an audience for you,’ ” Demeter says with a grin.

Paduan 16th Century. A Toad with a Toad, early 16th century bronze / Medium brown patina, Samuel H. Kress Collection (National Gallery of Art/NATIONAL GALLERY OF ART)

It was Demeter’s hope of attracting one particular audience — his old coworkers — that inspired him to begin creating a tour about dragons and other (real) reptiles. “I was just going to give it to the zoo crowd,” he explains. “I thought, ‘That’s the only way I’m going to get them down here.’ ”

Wilford Scott, the gallery’s head of adult education, soon caught wind of Demeter’s fledgling tour concept. “Selfishly, I was thrilled,” says Scott, who was curious to take the tour himself. Yet Scott had a bit of a bureaucratic dilemma on his hands: Under gallery rules, only staff lecturers — all of them art historians with advanced degrees — are allowed to design thematic tours.

Scott recognized that Demeter’s tour would be grounded in deep expertise, albeit not artistic. So he found a way around the technicality: He hired Demeter as an independent contractor to design a tour about reptiles in art.

After conducting extensive research, Demeter created an outline of his tour and gave Scott a dry run. Beyond content, Scott was looking for flow. “We’re really big on transitions,” he explains. (“Follow me,” it turns out, is a faux pas at the gallery.)

Scott needn’t have worried. Demeter infuses his tour with dry wit (“If God can fly, why does he need angels to hold him up?”) and casual warmth. As he enters each new hall, he and the guards exchange handshakes and pleasantries. Occasionally, Demeter will point out a statue that’s unrelated to the tour. “Remember that guard upstairs? This is her favorite piece.”

Not counting these bonus tidbits, the Dragon Tour covers six centuries of art, 10 galleries and a bevy of creatures. There are snakes painted so meticulously that Demeter can identify them by species, cartoonlike dragons locked in battle with Christian knights, and toad statuettes that look eerily real for good reason. Italian artists used to stun toads with vinegar or urine and then make “life casts” of them.

But the real joy of Demeter’s tour is his deep knowledge of reptiles and humankind’s remarkably diverse attitudes toward them.

Mercury, c. 1780/c. 1850. bronze, Andrew W. Mellon Collection. (National Gallery of Art/NATIONAL GALLERY OF ART)

Snakes were profoundly sacred to the Greeks and Romans, says Demeter. Aesculapius, the Roman god of medicine, carried a snake-entwined staff. And Mercury carried a “deluxe” version with two snakes, Demeter adds, as we peer up at a statue of the famous prankster. Thanks to confusion between those staffs, both live on in the logos of modern medical associations.

Renaissance scientists were fascinated with the aquatic world, Demeter says, contemplating a jampacked Dutch still life featuring fish, lizards and frogs along its base. Many joined with the 16th-century naturalist Pierre Belon in believing that frogs “fused back into silt” each fall, remained mud until spring and then resumed their frog form. They weren’t far off, by the way. According to Richard Emmer, a keeper at the Cleveland Zoo, aquatic frogs often rest partly buried in mud while they hibernate through winter.

A Qing Dynasty vase adorned with a serpentine dragon offers the chance to discuss Chinese notions about dragon metamorphosis, a 3,000-year progression from gemlike egg to carp-headed water snake and finally to mature winged dragon. Many believed that Chinese dragons had power over water, rainfall and floods, Demeter adds. And once again, this belief may have been inspired by observation. Demeter says that saltwater crocodiles, which roamed ancient China, are thought to be able to detect changes in air pressure and sense coming rain.

It’s clear that Demeter has developed a deep respect for the curiosity and keen observation that unite artists and scientists.

His Dragon Tour will be offered at 1 p.m. on July 17 and 24, when both tourists and locals are likely to be able to catch it. In the meantime, Demeter will be busy offering more traditional tours (all crafted with his inimitable care and wit) about once a week.

Wilford Scott hopes that Demeter‘s tour will be the beginning of a trend. He says the gallery has funds to hire more experts as independent contractors, if they have ideas for looking at the collections in a new way. “I’d be happy to hear from people,” he says.

Widiss is a freelance writer.