We can’t see them, but we know they’re out there: The dastardly pollens. The sneaky mold spores.

And thanks to the Pollen and Mold Center of the St. Louis County Department of Health we know which ones are in the air.

Hello, Pine, Cattail and Plantain.

Well, gee-whiz, it’s Ragweed. Back again, so soon?

Allergy and asthma sufferers, in particular, know by their sneezes, wheezes and coughs when there’s a mess of pollen and mold in the air. After all, it comes with the territory: St. Louis is smack-dab in the middle of the Middle West, where the changing array of seasonal plants and crops blast daily “hellos” into the air.

Wayne Wilhelm, supervisor of the Environmental Health Laboratories for the St. Louis County Health Department, understands that his staff’s reports on air quality are must-sees for people who are extremely allergic to pollen and mold. The daily counts serve as warnings that these airborne culprits might trigger asthma and other breathing issues.

We visited with Wilhelm and his staff on a recent morning to find out how they count pollen.

Take 1: The aeroallergen collector never rests

It looks a bit like a miniature spaceship, perched atop the roof of the county’s old animal shelter on Hunter Avenue in Clayton, but it’s actually a Burkard spore sampler.

The contraption sucks in surrounding air and traps airborne particulates onto a sticky glass slide on a mechanism that creeps along at 2 mph -- that's millimeters per hour. The slow-moving slide guarantees that pollen, mold and whatnot can continually stick to a fresh surface. The machine can be set to sample air during a 24-hour period or for as long as seven days.

Wilhelm said the Burkard landing site -- which overlooks Interstate 170 -- was initially chosen because it is on county property and fairly centrally located. The National Allergy Bureau recommends that the machine be located at least one story off the ground.

Take 2: Today’s pollen count is based on yesterday’s air

Wilhelm (above) said that he or one of his staffers collect the samples at about 7 a.m. Monday through Friday, replacing the used slide with a new one.

They’re on a timetable: The Pollen and Mold Center promises its loyal fan base – who range from individual residents to local meteorologists -- that the results will be available by 11 a.m. on the website or on a recorded message at 314-615-6825.

This day’s pollen sample was actually collected in a 24-hour period that began the day before, so there is a time delay: What you see today, you were actually breathing yesterday.

“We’re about 24 hours behind in giving you the actual numbers, but if you’re feeling bad today, tomorrow you can look at the count and say, ‘Oh, ash was really high or mold was really high. That’s probably what triggered me feeling horrible yesterday.’ Then you want to be watching those counts more closely," Wilhelm said.

Counts can vary due to temperature, wind conditions, humidity or precipitation -- and location.

“We’ll get calls from north county or south county saying, ‘Your oak count doesn’t seem high, but I’m having problems.’ They may live near more wooded areas than our sample is collected," he said. “And the weather may be nicer today than it was yesterday so the trees are responding, but I won’t know that until tomorrow."

The Burkard can be set up for 24-hour sampling, or for longer periods, such as weekends. The county lab does not check samples on weekends, so the Monday count is actually a compilation of air collected between 7 a.m. Friday and 7 a.m. Monday.

Take 3: Meanwhile, back at the lab

On this day, Tom Makara (above) would be the official counter. Pollen and mold spores are not visible to the naked eye, so he first prepped the slide with a red gel stain so they would show up under his microscope.

In simple terms, he set his microscope to 400x magnification and counted the pollen trapped in a path across the length of the slide -- which would account for the entire 24-hour period. He then made a second pass across the same path at 1,000x magnification allowing him to see the mold spores.

The process can take several hours, depending on how much pollen and mold is trapped on the slide.

The county lab belongs to the National Allergy Bureau, a section of the American Academy of Allergy Asthma and Immunology’s (AAAAI) Aeroallergen Network. The network produces current counts of pollen and mold spores nationally, reported by about 85 counting stations located throughout the U.S.

The county’s counters -- Wilhelm, Makara and Nora Pullen -- are certified by the AAAAI.

On the lab’s walls are posters featuring various pollens, tinted by red stains, as they would appear under a microscope. Wilhelm, who’s been doing this for about 20 years, said it takes at least a year for analysts to become proficient at recognizing the various pollens in their area.

Although it takes longer to identify specific pollen totals than if the analysts were to just provide a general count, Wilhelm said the process is more helpful to allergy sufferers.

“If you’re allergic to oak, for example, and I’ve heard of people doing this -- they’ll take a vacation out to Arizona or somewhere to get out of St. Louis for a week and let the worst of the tree pollen do its thing. Then they’ll come back and manage their symptoms with over-the-counter or prescription medicines. Depending on how bad they suffer, people have gone to different extremes," he said.

Take 4: 1,001, 1,002, 1,003, 1,004, 1,005 … whew!

Makara (above) used a blood cell counter, which can keep track of a dozen or so separate totals, to tally each pollen and spore visible along the narrow field of view he selected on the slide.

The individual counts, which can range into the thousands on a bad air day, are then entered into a computerized spreadsheet that uses a formula to figure the total number present during a 24-hour period. The formula is based upon exposure time, volume of air sampled and the number of pollen grains or mold spores counted.

Wilhelm calls the process “a labor of love.” Though the sampling devices have changed through the years, the county health department has been providing this service to area residents since 1960, he said.

This will come as no surprise to allergy sufferers, but Wilhelm said this spring’s warm temperatures put pollens ahead of schedule: tree pollens peaked sooner, and grass pollens appeared earlier.

“The last phase of the season is weed pollen, and weed pollen typically comes out in late July or August and peaks around Labor Day when ragweed -- hay fever -- is at its worst. But I have a feeling we may see it peak early," he said. “Quite possibly the hay fever season could come earlier and last until the frost, which means it will last longer."

All in all, Makara said this particular day was a good one for pollen -- some reportable grass and plantain -- but mold was high at 13,551.

Oh, and there was this: He spotted a ragweed pollen, the first of the year.

Take 5: What happens when health department moves?

The lab’s website posts 60-day records of the daily counts, which are helpful to people trying to figure out what is causing their symptoms, Wilhelm said.

But the actual records go back for years and can be used to study changing trends in air quality.

When the county health department moves to its new facilities in Berkeley in July, the Burkard will be landing on a new rooftop.

Wilhelm doubts that the move will have a major impact on the allergy and mold counts, though the new site, which is still near Interstate 170, might be surrounded by less vegetation than it is currently.

“It’s going to be interesting," he said. “But I don’t think we’re moving it enough of a distance. If we were moving it further west I think we might see a greater variation. The more rural we would go, I think that would be a difference."