Mosquito abatement courier's footwear.

Straddling his red bicycle by a sewer drain in Dolores Park, Evan Gerardo holds up a small biodegradable bag of dry brown nuggets, what he calls a “sewer snack.”

Evan Gerardo, mosquito abatement bike courier

It’s bacteria packaged in a medium that brings to mind breakfast food more than mosquito annihilation.

“They look like Grape Nuts,” he says. “I’m convinced they are Grape Nuts,” he adds mischievously.

Gerardo is blond and unshaven under his bike helmet, his nose sunburned and peeling. He’s wearing a neon vest that says Pestec, but that’s where his official uniform ends; the rest of the outfit includes a plaid flannel shirt, jeans, a black bike bag, and a pair of paint-flecked cowboy boots, so worn out they’re cracked at both ankles. His red bicycle is also splattered in paint: red, blue, pink.

Gerardo is member of the San Francisco Mosquito Abatement Courier — MAC — team, run by Pestec, an eco-friendly pest management company. San Francisco contracts with Pestec to scour the city in search of catch basins, which are the perfect breeding ground for disease-carrying mosquitoes.

Vectolex, also known as a sewer snack.

In recent decades, free from the worries of mosquito-borne illnesses like malaria and dengue fever, Californians considered mosquitoes to be mostly a nuisance. Then, in 1999, West Nile virus was found in humans in New York City. The virus probably originated with birds in Israel.

West Nile virus is normally transmitted among birds through mosquito bites. Humans tend to be a dead-end for West Nile because we don’t amplify the virus sufficiently to spread it to others through mosquito bites. But it can kill us, and in 2009, at least 32 people died and hundreds became seriously ill from West Nile in the United States, according to the Centers for Disease Control and Prevention.

From New York, it took West Nile three years to show up on the CDC’s radar in California, and infections here peaked in 2005 at nearly 900 reported cases, 299 of which resulted in encephalitis or meningitis, inflammation of the brain or of the brain and spinal cord membranes, respectively. [See graph below]

Estimates of unreported California cases in 2005 are upwards of 80,000. That’s because 80 percent of those contracting West Nile don’t have any symptoms. The other 20 percent get flu-like symptoms, including fever, aches and exhaustion. Only around a third of a percent get encephalitis or meningitis.

The best way to avoid getting West Nile is to get rid of mosquitoes, by minimizing standing water and by killing the insects as larvae. In San Francisco, the larvae are killed without the use of motorized vehicles.

“None of that driving around in trucks and pumping things in ponds,” Gerardo says about the city’s zero-emissions approach to mosquito abatement.

He is one of eight people who bike or walk every single street and open space in the city from January though October, looking for the drain access to more than 20,000 catch basins. The basins collect roadway water and debris, only draining to the sewer when the water level rises sufficiently, leaving San Francisco with lots of standing water under the roads. If there were no catch basins to divert the water, the roadways would wash away over time.

When Gerardo finds the drain to a catch basin, he treats it with a sewer snack of bacteria spores called Bacillus sphaericus. Mosquito larvae eat them. Once the bacteria enters a little larval mosquito gut, digestive processing breaks down two of the previously nontoxic bacteria proteins into smaller proteins, making them toxic to the larva. The proteins stick to the lining of the larva’s gut, eventually killing it.

Looking for catch basin in Dolores Park.

Each catch basin is treated roughly every three weeks. The team member who treats it types the location of the drain and other characteristics into a cell phone, marking the spot by GPS, and spray paints a dot on the curb. The color of the dot changes every cycle and is layered onto previous markings. That makes it simple for the city or anyone else to see when a catch basin was last treated.

It’s really only the female mosquitoes that cause all the trouble; only the females bite. “They need the protein in the blood to produce viable eggs,” says Erin West, who manages the abatement team.

The male mosquitoes don’t even have the right kind of mouth shape. They’ve got a feathery proboscis that works better for eating nectar from flowers.

In addition to sewer snacks and spray paint, Gerardo hauls other items along for the trip, in the event he’s stranded out in the far corners of San Francisco without transportation.

“I’ve got enough tools to rebuild a bike in there,” he says, patting his bike bag.

“I usually break a chain every couple weeks.” He admits that others on the team might be gentler to their bikes. Nonetheless, the job entails going into grassy and forgotten areas, down glass-strewn alleyways, off-roading in parks, and climbing up and down steps, curbs and hills. Gerardo rarely dismounts, preferring to take his bike along every inch of the way.

“I’ve destroyed a wheel, two derailleurs, countless toe clips, cassettes…a crank set came off once…I just cracked my seat last week.” The seat broke at the bolt somewhere along Market Street. “Me and the whole seat just went like this,” he says, motioning backwards. “The bike just kept going.”

The couriers bike an average of 15 miles per day in the course of their jobs, not including the trip back to the office in Bayview, according to Erin West.
In some neighborhoods, people dump almost everything imaginable into the drains, like septic tank waste, butcher shop leftovers and alcohol bottles. Chinatown has the most “amazing” drains, Gerardo says. “Those people own it down there.”

The Mission is “easily one of the best sections to work in,” according to Gerardo. It’s full of people and restaurants, and many of the catch basins are in alleyways, which are always interesting — you’ll find people barbecueing, spraying graffiti, camping out, even school kids cutting class. “They give you dirty looks,” he says. And steal your spray paint if you’re not watching.

In the team’s first few years turnover was quite high, since riders have to be meticulous and yet quick enough to cover a lot of territory. Now there is a stable crew of riders, according to West. The job has its perks, among them seeing every street in San Francisco and working outside. Also, interesting stuff turns up in the gutters.

The worst are rats and cockroaches. “Money is definitely the best one,” Gerardo says, though he won’t fish it out if he can’t reach it.

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Anrica is a science reporter and twice Cal grad, with a degree in engineering and a master of journalism. She's a Bay Area native and lives in Oakland. She's enjoyed wide-ranging professional endeavors, including shoveling manure, researching human signaling proteins, volunteering in a leprosy hospital, using an atomic force microscope, and modeling the electricity grid.

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  1. Are the sewers too flat to have positive drainage when it’s not raining? Why is there standing water in the first place?
    Can they ramp up the bottom of the catch basin with concrete so it has min 2% slope?

  2. I wish we had this in Solano County!I was bitten by mosquitos many years ago-I had flu like symptoms-I went to the Dr.twice-and was told I had the flu-I was dizzy and my neck hurt and I got a rash-I was rushed to The ER and in Intensive care for 10 days-at 1st they thought I had West Nile Virus-it turned out I had contracted Meningitus-my memory has not been the same!Please protect yourself and wear bug spray also-I wouldn’t wish this on anyone!!!!I appreciate what these people are doing!!it could save the life of someone you care about!! Willie Miller-Castillo

  3. Thanks for the great article! Would just like to add that the term “Sewer Snack” was coined by former MosQuito Abatement Courier extraordinaire Jess Meek who now works for the Globe Bicycles marque.

    Skeeter D

  4. Oh! So that’s what the dude on a bike spray painting a stripe near a drain was all about. I was wondering!

  5. Awesome article! Really confusing headline! It did get me to read the article, though (mostly, the bloodthirsty females part).

  6. Thank you for the wonderful article!!! We are proud to partner with SF Water in the fight against mosquitoes bugging the residents of the City and County of San Francisco to keep all of us healthy.

  7. SF had a pretty good mosquito abatement program before Prop 13, though it was probably some kind of poisonous spray. Thanks for this.