Weird Water Sources

Don’t water down the inspection! Water can gather in many places you might not consider, including polluted water.

© Olga Gorevan | AdobeStock
You’ve heard it many times: mosquitoes can develop in as little water as a soda cap. Trying to find the water sources that mosquitoes are developing in, and addressing them, are part of a successful mosquito management plan. Books, trainers and researchers make it sound so easy: find all the water sources and all your problems are solved. Finding all the water sources that mosquitoes are living in is nearly impossible though. While there are always the obvious places (birdbaths, old tires, potted plant bases, etc.), looking to some of the less obvious spots can help improve your efficacy. If you can deal with the problem better, you increase customer satisfaction.

YOU DON’T KNOW KARST! A few years ago, the yellow fever mosquito was found to have overwintering populations in Washington, D.C. This was well north of where it was assumed their range ended. While we know that mosquito ranges are expanding due to climate change, this climate change was entirely man-made. The insects were found in urban karst areas. I admit I had to look up what a karst is. Essentially, these are concrete caverns, areas such as tunnels, sub-basements, stormwater drainage systems, sewers and any underground structure that can have water. This typically isn’t as much of a problem in residential areas, though you may get some culverts or sewers that are issues. For those working in urban areas, think about all the underground sites that might be providing mosquito habitats. Think about underground parking structures and basement mechanical rooms. These underground structures not only hold water, but also hold heat from the structures above. I once found mosquitoes breeding in a below-ground receiving dock in the winter in the Northeast. Water had gathered in the area below the raised dock and the area retained the building’s heat.

Fun fact:

It’s not just the United States. Mosquito species are expanding their range further north into Canada than ever before. The eastern tree hole mosquito (which transmits dog heartworm) was found recently breeding in Canada.

Courtesy of Chelle Hartzer
Compost, which is good for the planet…and also good for mosquitoes!
They look a little sad right now because it is winter, but come spring and summer, these won’t be attracting mosquitoes!
Courtesy of Chelle Hartzer

YOU GONNA DRINK THAT? It’s no surprise that some mosquito species are hardy and can live in water sources that seem too polluted to be viable for any life. Don’t ignore these! A study looked at filled windshield wash basins at gas stations. You can guess where this is headed: they found one-third of sampled basins had mosquitoes breeding in them. If you have ever looked at the liquid in these buckets? It’s pretty gross (have you ever washed your windows and they wind up dirtier? And those basins have cleaning fluid in them!). Yet the mosquitoes could successfully develop. Doing inspections for these filthy water sources and trying to remove them is as important as removing cleaner water sources. In residential areas, think about outside trash cans that may have water (or other liquids) pooling in the bottom. In urban areas, trash dumpsters also can retain liquids. Confession time: I found mosquitoes breeding in my outside fire pit filled with ash in it. It had no drainage holes and with heavy rains, had accumulated enough water that, despite the old ashy coals, still managed to be a source.

UH-OH! Speaking of polluted water sources, here’s another reason to ask your customers to clean up: a study looked at water sources that were contaminated with different animal feces. They found many of the “dirty” waters to be more attractive to female mosquitoes than cleaner water sources. They looked specifically at feces from livestock animals, but customers with pets, like dogs or other small mammals, may want to do a better job with cleaning up the animal waste. Even cleaning yard waste is helpful. The dead leaves, grass clippings and other yard waste contribute to extra nutrients in nearby water sources. Extra nutrients mean extra food for developing larvae. In a completely unscientific study, I had a few mosquito traps places around my yard, testing to see how well they worked. I did notice the one nearest my compost pile typically had more mosquitoes.

The offending fire pit.
Courtesy of Chelle Hartzer

Fun fact:

The neighbors are quiet but they are still a problem. A study from Europe looked at mosquito breeding sites in cemeteries. The researchers found up to 72 percent of water sources in cemeteries had mosquitoes in them.

ARE YOU SWEET ON ME? While finding the water sources is important, here is one more piece to add to your arsenal of inspection locations. Look for nectar sources. Male mosquitoes, in their short adult life, drink nectar from flowering plants. Well, females mosquitoes do too. In fact, some small studies have shown more adult mosquitoes near flowering plants than other areas of residential yards. We know that we can not apply products to flowering plants — we want to protect pollinators. However, the recommendation can be made to homeowners to reduce the flowering plants or to move them further away from outdoor living and play areas. Particularly for businesses like restaurants that have outdoor seating areas, changing their landscaping to non-flowering plants can significantly reduce mosquito interactions. I purposely don’t keep flowering plants on my deck or patio since that is where I spend the most outdoor time. I keep my flowering plants at the front and sides of my house.

Water and warmth, who cares that it is snowing outside? Certainly not the mosquitoes!
Courtesy of Chelle Hartzer

Fun fact:

Be positive. A recent lab study showed mosquitoes were significantly drawn to type B blood. This was only done on one mosquito species so more research needs to be done on other species.

HAPPY WATER SOURCE HUNTING! The old adage of “just a soda cap worth of water” is very true and makes it hard to find every water source that mosquitoes can be using. It is not going to be possible to find every last water resource at a location and remove it. That doesn’t mean you shouldn’t try. Also, remind customers about the importance of removing as much of the water sources as they can on a weekly basis. Help them identify those areas that are a concern. When mosquito problems seem to be persisting, or are found in areas you don’t expect them, start thinking “outside the birdbath” and look for anything that might be holding water…no matter how polluted that water source may be.

Chelle Hartzer is a board certified entomologist at 360 Pest and Food Safety Consulting. Contact her at

March 2022
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