A zombie ant, a pair of bats and a gorilla lurked around the shadiest alcoves of a Cook County forest preserve on Saturday, scouring the earth for decomposing life forms.

But the pack of monsters wasn’t intending to feed on the dead organisms.

Instead, the group of fungi partisans celebrating Halloween was conducting a regular survey to document the presence of fungi, a kingdom of life that often thrives in the creepiest places.

“When we’re collecting, it’s not to eat — it’s to build a baseline understanding of what’s growing and where and when because mushrooms for so long, and fungi in general, have been understudied in science,” said Kate Golembiewski, events chair of the local mushroom club, the Illinois Mycological Association.

Like the subject it studies, the mushroom club abides in the shadows — specifically, the shadows of more celebrated outdoor hobbies such as birding, hiking and gardening. But its members are hoping to change that. After all, fungi are genetically more closely related to humans than other stalwarts of nature including trees and grass — and like people, fungi must eat to survive rather than rely on photosynthesis.

Golembiewski, a 35-year-old science writer at the Field Museum, got hooked on mushrooms after attending an annual show hosted by the club at the Chicago Botanic Garden during Labor Day weekend in 2022. The Northwest Side native, who went to the local fungi exhibition to see her friend Matt Nelsen, a colleague who is the club president, was blown away by the specimens she saw, including some that looked like bird nests. She became a dues-paying mushroomer that day.

About two years later, on Saturday morning, Golembiewski and Nelsen — one dressed as a foul-smelling mushroom and the other pretending to be a dead ant infected with a fungus — tromped around St. Mihiel Woods-East in Tinley Park with about 30 other club members, scanning the dirt, fallen trees and sticks for fungi.

“We have a lot of birders in our group,” said Liz Weinstein, the club’s survey chair, who also likes birding. “They’re always looking up. We’re always looking down.”

Mycology is the study of fungi — hence the Illinois Mycology Association. During mushroom season in Illinois, mid-April to early November, the club conducts surveys around Chicagoland a few times a month. Earlier in October, the club, which is more than 50 years old, did surveys near Rockford and in Kenosha.

While conducting a survey, club members fan out across a spot in nature, individually or in groups, for a few hours and gather up various species of fungi. Mushrooms are the fruiting bodies of fungus; they are like what an apple is to an apple tree.

Some carry their findings in plastic containers with compartments. Others use baskets. At the end of a survey, members lay out their specimens on a picnic table or tarp and try to identify what’s there.

“I like a stumper — finding something where everyone at the table is like, ‘Huh, don’t know what that is,’” said Weinstein, a 48-year-old mushroom photographer.

While conducting a survey, club members don’t usually wear costumes.

About a dozen of the roughly 30 people who participated in Saturday’s survey — billed as “a haunting in the woods” — dressed up. Some donned traditional Halloween garb, while others, of course, pretended to be their favorite fungus.

Golembiewski went to the survey as a “bridal veil stinkhorn,” a mushroom known to be stinky. (She did not actually stink.) The mushroom has a structure that hangs near the mushroom’s cap and looks like a skirt made of lace. In imitation, Golembiewski wore a brown knit hat and a white piece of lace with skulls attached to a brass ring that rested on her shoulders and a hula hoop suspended around her knees.

Nelsen’s costume — which was made out of trash bags, a wooden dowel, a styrofoam ball and other materials — had as much, if not more, thought put into it. He went as a zombie ant — an ant infected with the Ophiocordyceps unilateralis fungus.

When an ant gets infected with the fungus, it starts behaving erratically and eventually uses its mandibles to attach itself to the underside of a leaf, where it dies hanging upside down. A fungal structure eventually protrudes out of the back of the ant’s head area and rains spores down on other ants running around on the ground.

The TV show “The Last of Us” is set during a pandemic caused by a mutant form of the zombie-ant fungus. Nelsen said the fungus probably won’t start infecting humans any time soon because it’s been infecting a particular group of ants for tens of millions of years and hasn’t spread to other ants living nearby.

“There’s a 40- to 50-million-year-old leaf fossil that has a bunch of (zombie ant) bite marks on it, and so that is evidence that this sort of infection has been going on for 40 to 50 million years,” Nelsen said.

Weinstein said she organized the haunting in the woods because Saturday was Golembiewski’s birthday and Golembiewski loves Halloween. It’s natural for people who love Halloween to also love mushrooms, according to Golembiewski. Mushrooms often jump out around dead and decaying things. Also, many thrive in spooky places where it’s shady, moist and cool. Golembiewski said she learned about the haunting after discovering information about it while dropping contributions to a club newsletter into a shared Google Doc.

“They had written this whole thing about a haunting in the woods, and I was so delighted,” Golembiewski said. “I was just grinning from ear to ear.”

The surveys, in addition allowing club members to experience the joy of learning about, discovering and picking cool mushrooms, are valuable to science in a number of ways.

Nelsen said the club has documented the presence of fungus species at certain sites for decades. A long-term data set that shows a particular mushroom has begun fruiting earlier or later in season in recent years could be evidence of climate change. The club can also monitor the spread of invasive species of fungus.

Some specimens the club gathers get preserved at the Field Museum. Nelsen said a few members of the club are working on a project to sequence the DNA of Chicagoland fungi.

John Willis, 12, of Edison Park, was one of the youngest mushroomers who attended Saturday’s survey.

“The survey yielded some great results,” John said. “The sulfur shelf and hen-of-the-woods (mushrooms) are really interesting.”

Willis, who is considering studying mycology in the future and received a club membership for his birthday n October, said he became interested in fungi because of their potential health benefits and because they are “such an unexplored frontier.”

Indeed, scientists are aware of about 150,000 species of fungi and estimate that there could be more than 3 million species in all, according to Nelsen.

“I think part of the reason we have this huge disparity … is that so many of these are so tiny and are cryptic and hidden away,” Nelsen said.

“They’re living in their food, and we’re just alerted to their presence when they’re there for that brief window of the year. And I think there’s just fewer people interested in them.”

Because of a slight physical disability, Golembiewski won’t ever be able to take on hobbies such as mountain climbing or preparing for the Chicago Marathon.

But for a mushroomer, being able to take it slow is a virtue that pays off.

“If you are walking at a good clip through the woods, you’re gonna miss half of what we’re finding,” Golembiewski said.

“Being able to say, ‘OK, cool. I’m gonna park myself here and just kind of go over this old fallen tree inch by inch’ — you wind up finding 10 things that you absolutely would have breezed right past.”