Minnesota Mosquitoes: by the Month
January 7, 2025
The first mosquito larvae of 2025 were found on March 17th, about when we would expect them to show up.
Dry weather in March means the season might start slowly, but last year's weather could contribute to a mid-summer surge.
Signs of spring are beginning to show in Minnesota - snow is mostly gone, temperatures are starting to climb, and MMCD staff are finding deer ticks on the ground and mosquitoes in the water. As everyone begins to put away their winter gear and get excited for summer, we thought we'd offer a preview of the impact mosquitoes and ticks might play on our summer fun.
2024 was an unusual year for mosquitoes - the Twin Cities saw above average rain throughout May, June, and July, but high mosquito numbers did not follow. This is likely due to the preceding three years of drought conditions and low numbers of some of the more common nuisance species. After a year of rain, many of those will bounce back in 2025 - and if we see similar rainfall totals as 2024, some may return in big numbers.
What kind of numbers? The MMCD Entomology lab has developed a model to predict the abundance of cattail mosquitoes (Coquilletiddia perturbans), a unique species that hatches the previous fall, overwinters in the water as larvae, and emerges around the 4th of July. This species has been mostly absent over the past three years due to drought conditions impacting the marshes that make up their habitat. However, the MMCD model projects a high number of cattail mosquitoes returning in 2025:
The cattail mosquito prediction model which appears in the MMCD Technical Advisory Board report.
The model is projecting that we may see close to 100 cattail mosquitoes per trap on average, which would be similar to 2020, the last time this species was out in abundance. This is a single brood species, so their number are low in the spring, spike in early July, and then gradually decline throughout the rest of the summer.
A drier winter means the mosquito and black fly season might start slow
An adult mosquito in a hockey rink, found hiding out in the winter months.
That may be bad news for the middle of the summer. There may be good news at the moment for spring, however. According to MMCD Assistant Entomologist, Dr. Scott Larson, "2023 was the record year for spring Aedes and 2024 had the second most spring Aedes on record. If we had some snow on the ground or get a lot of rain soon those could be troublesome again this season, but it looks like their preferred habitats (vernal pools and snowmelt) are or will be dry when the season starts." The "at the moment" in the second sentence of this paragraph is doing a lot of heavy lifting, as heavy spring rains or a late season snow storm could change our fortunes. Last year a dry winter was followed by heavy snow and rain in the early spring months, leading to high mosquito abundance in May and June.
River levels are currently trending below average and there is not much snowpack left to cause a surge in their levels. Again, spring snow or rain could change things, but currently MMCD Black Fly Specialist Carey LaMere is predicting average or below average numbers of black flies (biting gnats) to start the year.
Spring of 2025 is trending cooler than 2024.
Based on temperatures, air work likely to begin in late April.
At the Metropolitan Mosquito Control District we track days above 40 degrees Fahrenheit to get an estimate of when we can expect mosquitoes to become active. We also use this metric to help determine when we need to begin our treatments via ground or helicopter in ponds and wetlands where larvae are present. So far 2025 is trending cooler than 2024 and long-term weather projections suggest we will begin helicopter treatments in late April.
Any planned helicopter activity will be posted on our website and social media with a list of cities. Throughout the summer helicopter activity is largely dependent on precipitation, so check back for our weekly updates on the current conditions.
Long-term climate predictions suggest back to dry weather for 2025.
Predicting the weather a few months from now is a difficult task, but we look to the National Weather Service for long-term predictions on temperature and precipitation. Their model suggests that June, July, and August will be drier than normal in Minnesota. If this holds true, then Aedes vexans, or summer floodwater mosquitoes, might not be that prevalent. This is our most common mosquito in most years, but it is heavily dependent on rain and so a lack of it might keep their numbers low for one more year.
Last year's predictions by the National Weather Service suggested that Minnesota was on the edge of a below average and a normal precipitation pattern and it turned out to be quite a bit above average. A lot can change between now and mid-May, so we will continue to look at weather patterns to determine the best course of treatment.
Our seasonal species abundance surveillance using traps and sweep nets to collect adult mosquitoes will begin in May so we won't know the results of these predictions until then.
Ticks are active already and will likely be out in similar numbers as recent years.
MMCD staff member Abbey Novotny from our Andover facility gets the credit for finding our first deer tick of 2025 on March 27th. We suspect they've been active for some time and have had numerous reports from members of the public that they've been found throughout the Twin Cities already.
Predicting tick numbers is tricky because they have a multi-year life cycle and rely on a variety of factors. The extreme cold we experienced in January and February may depress their numbers a bit, especially for lone star ticks which are not very common this far north. On the other hand, MMCD Tick Specialist Janet Jarnefeld believes that last year's rain might help the tick population recover from the preceding three years of drought. Expect this year's tick season to feel more like "normal" which means they will be abundant in long grasses and wooded habitats in May and June especially.
Seasonal staff will begin work on April 14th so expect to start seeing MMCD trucks, helicopters, and drones in your community very soon. We will continue to provide updates throughout the season on anything that may inform or alter our predictions.
Be sure to revisit MMCD.org every week this summer for updates on mosquitoes, black flies, and ticks!
