ST PETER — The third- and fourth-graders already had smelled fox urine, gazed upon rabbit scat and heard stories about maggots eating the infected flesh of an elderly woman.

But the true test of their senses was making its way around the room on a paper plate. Those who wanted an A+ in Chrystal Dunker’s “The Icky, The Gross and the Yuck — It’s Grossology!” session had to engage their tastebuds, too.

When the paper plate reached Kadence Bran De Leon, she looked down at dozens of squirming, squiggly mealworms and took a few moments to decide how to proceed. But then, the adventurous spirit took over.

“It’s actually not that bad,” Kadence said, grinding a mealworm between her molars. “I think I can taste its exoskeleton.”

Dunker, from the Prairie Ecology Bus Center mobile nature center, was a presenter at the Science & Nature Conference Tuesday at Gustavus Adolphus College. The goal of the annual conference, put on by South Central Service Cooperative, is for students to delve deeper into science and nature topics.

Hundreds of regional third- through sixth-graders attended and took in sessions ranging from Mysteries of the Minnesota River to The Rotten World of Fungi.

Dunker’s session was all about “gross things in nature,” she said, asking the students what icky things they had seen firsthand.

“I have seen a dead fish,” a girl said. “My dad killed a chipmunk,” a boy said.

Dunker topped both many times over before the 55-minute session was up. The kids saw a video of a large leech encircle a small salamander and suck blood out of its abdomen, for example. Blood-sucking leeches drink 10 times their weight in blood and then don’t eat again for nine months, she said.

“Some days I wish I was a leech,” Dunker said. “It would save me some time.”

Leeches also have been used in the world of medicine for many years, she said. Today, leeches are used to help blood vessels reconnect when a person has a severed toe or finger reattached, she said, because the suction helps pull the vessels together.

The kids saw vials of red blood (from animals with a backbone), blue blood (from specimens such as clams, muscles and slugs), and white blood (from bugs). They also watched a close-up shot of a skunk’s behind as it sprayed its stinky defense liquid, which can shoot up to 20 feet.

The pictures of 2-pound elephant scat and tiny rabbit droppings garnered a few laughs.

“It looks kind of like Cocoa Puffs,” she said. “If you see this on the ground, trust me, nobody drops cereal.”

The keynote speaker — Bob Kann, an author, storyteller and magician — gave a talk at the beginning of the day that encouraged students to become actively involved in bettering the planet. Breakout sessions were led by college professors, master naturalists and staff from Minnesota Department of Health, Minnesota Department of Natural Resources, Minnesota Pollution Control Agency, Science Museum of Minnesota and Zoomobile, among others.