October 20, 2021
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Brace yourself for mosquitos

By: Stephanie Derammelaere
April 12, 2019

The abundance of heavy rainfall and flooding the county has experienced this winter is expected to intensify the production of mosquitos this spring as the weather gets warmer. Experts caution residents to do what they can to prevent mosquitos from breeding around their homes to minimize the risk of West Nile, Zika, Saint Louis Encephalitis, and other viruses. Being proactive now before the weather warms up can help improve the safety for the whole community. 

“We’ve had so much rain and water standing so far this year,” says Nizza Sequeira, Public Relations Director for the Marin/Sonoma Mosquito and Vector Control District (MSMVCD). “We’re out checking all of those large areas that we’re aware of and we are finding a lot of mosquito larvae. But we don’t know what’s in people’s backyards. All of this rain probably built up a lot of backyard containers that people have. That’s going to be a real issue if folks haven’t dumped out that water.”

So far this year the MSMVCD has not found any disease activity, but one sample group of mosquitos did test positive for West Nile Virus in Petaluma in 2018. 

Since mosquitos breed in standing water, it is important to remove any containers that may retain water such as buckets, wheelbarrows, cans and jars, trash containers, and even tarps after rainfall. The MSMVCD recommends dumping water from items stored outside such as kiddie pools and plant saucers, and disposing old tires. Regularly clean out birdbaths and animal water bowls, and keep swimming pools and hot tubs properly chlorinated. Clear out rain gutters and debris from drainage ditches to allow water flow. In addition, a sump pump can remove standing water that may have accumulated under one’s home. 

There are 23 different species of mosquitos in our area, and they all have different egg laying patterns and preferences, flight patterns and ranges, and biting habits. MSMVCD can come and inspect which type of mosquito is being a nuisance to a resident in order to determine where they could be laying eggs. For example, the mosquito carrying West Nile Virus lays her eggs in septic tanks, so it’s important to make sure they are properly sealed and that vent pipes are screened. Residents should also properly screen or secure lids on rain barrels or water storage containers and not over-water lawns. 

“One example of a common mosquito we find is the Culex Pipiens, or house mosquito,” says Sequeira. “You’ll find them in septic tanks or highly polluted water. They bite at night and they can transmit West Vile Nirus and Saint Louis Encephalitis. Another mosquito that is quite abundant, especially as we come into spring time is Aedes Sierrensis, also known as the Tree Hole Mosquito. This mosquito is not a vector of any human disease, but it can transmit dog heartworm.”

If a resident in the county suspects a mosquito problem, the Marin Sonoma Mosquito & Vector Control District will come and check the resident’s home, inspect all known sources of mosquitos in the area, and set traps if necessary. This is a free service MSMVCD provides.

MSMVCD will also provide, free of charge, mosquito fish that can be stocked in permanent water features, ponds, horse troughs, or any standing water that is at least 18 inches deep. These fish can eat up to 500 mosquito larvae a day. The district can deliver the fish directly to a home or residents can pick them up directly at the office in Cotati. Because the fish go into a hibernation mode during the cooler winter and early spring months, the district does not provide them until May, the exact date still to be determined. 

Sequeira does advise residents though, that this time of year a swarm of small flying insects does not necessarily mean mosquitos. 

“This time of year we get a lot of calls from residents saying ‘I have swarms of mosquitos over my lawn or near my front door’ and they’re actually not mosquitos, they’re insects that resemble mosquitos,” says Sequeira. “Generally they’re midges and they look very similar to mosquitos. We do not control midges. While these large swarms of insects can be frightening or annoying to some, they pose no risk and thankfully are short-lived. But if residents find that they are being bitten, they can call us.”

The MSMVCD generally uses two different larvicides, bacillus thuringiensis israelensis  (Bti) and bacillus sphaericus (Bsph), to minimize the number of adults that emerge in a body of water. Besides reducing the risk of diseases, it also decreases the need for adult mosquito control. Bti and Bsph contain naturally occurring bacterium found in the soil and quickly kills mosquito larvae without harming surrounding livestock, wildlife, humans, or habitats. 

“Our district has always been very aware of the environmental issues,” says Sequeira. “We were one of the first districts in California that quit using organophosphates. We’re trying to do our best.”

To report a mosquito problem, call 707-285-2200 or visit, or visit the MSMVCD office on 595 Helman Lane in Cotati. The MSMVCD also provides free rodent control advice and free home inspections, and in-ground yellow jacket nest control. The district will be holding a free open house for the public on May 18 to raise awareness of the services they provide and educate residents on how they can protect their health.