Pest Control in Chaska, Minnesota

Brick city, river city: the local backstory

According to the City of Chaska, the 1851 Treaty of Traverse des Sioux opened the site, then known as Little Rapids, to settlement, and that August Thomas Andrew Holmes claimed a 20-acre clearing as the town site. The name comes from a Dakota word often given to a first-born son. Long before that, the city notes, the area’s first inhabitants are believed to have been Mound Builders, whose communities are marked by the mounds in City Square.

What made the town was its clay. The city dates brick making to 1857, and the Minnesota Historical Society’s MNopedia describes a deposit of yellow clay over blue that ran roughly twenty to forty-five feet deep. Around 1900, six brickyards employed about 600 men, and roughly thirty percent of all brick used in Minnesota came from Chaska. The cream-colored product went into the basement of the State Capitol and the prison at Fort Snelling, as well as schools, houses, barns, banks and churches. The last yard, Klein’s, closed in 1971.

The mining left holes, and the holes filled with water. The Lower Minnesota River Watershed District describes Courthouse Lake as a former clay mine that is now 57 feet deep, 12 acres in area and stocked with trout by the DNR, and Brickyard Clayhole Lake as another abandoned clay pit nearly 40 feet deep. They are the most visible reminders of the brick era, and the Army Corps of Engineers’ flood-control design for Chaska included upgrading and extending the levee system around Courthouse Lake.

The levee and Chaska’s mosquito seasons

Chaska grew up on the river bottom, and flooding has been a fact of life. A U.S. Geological Survey report from 1981 sampled East Creek, Chaska Creek and Courthouse Lake before a U.S. Army Corps of Engineers flood-control project, and noted that the lake had recovered from past inundations by Minnesota River floodwater. Today the Watershed District describes Chaska Creek as a seven-mile stream confined to a concrete channel around the west side of the city that empties onto the Minnesota River floodplain after passing through the flood-control levee.

That levee was tested in June 2024. The city reported that the river crested at 34 feet at the Highway 41 bridge, just short of the 1965 record of 34.25 feet, while its certified levee is built to 41 feet. City crews also explained a less obvious problem: water collects on the town side of the levee from rain that falls while the flood gates are closed and from groundwater that seeps up from underneath, and lift stations have to pump it out.

For mosquitoes, the floodplain is the important part. The Metropolitan Mosquito Control District (MMCD) says the most common summer species in Minnesota, Aedes vexans, lays its eggs on moist soil at the edges of ponds, swamps and other wetlands; rain washes the eggs into the water, the larvae develop in five to seven days, and the adults can fly more than 20 miles from where they hatched. A wet spring or a high river that leaves low ground soaked is exactly the setup for that species, and a yard well away from the valley floor is still within its flight range.

MMCD adds two other seasonal waves. The cattail mosquito spends the winter as a larva attached to cattail roots and emerges in a single brood, typically most common around the Fourth of July before dropping off quickly. The tree hole mosquito breeds in dark water in tree holes and waste tires and is a known carrier of La Crosse encephalitis, which the District notes can be harmful to children — worth remembering in a town that MNopedia places in the old Big Woods, where mature shade trees are common.

What MMCD does in Carver County, and where a private applicator comes in

Carver County is one of seven metro counties in the District, which the Legislature created in 1958. MMCD is funded through property taxes and makes no separate charge for its work, which centers on finding and treating larvae in wetlands and other breeding sites. Its FAQ is clear that the District does not spray private property unless there is a threat of mosquito-borne disease in the area. For questions about District work near your property, its line is (651) 645-9149.

That leaves the backyard to the owner. MMCD’s Resident’s Guide emphasizes removing standing water — buckets, tarps, clogged gutters, bird baths, unused pools and old tires — and treating low spots that stay wet for more than three days as potential breeding sites. The District also names Culex mosquitoes, which favor containers, tires and catch basins, as the Minnesota group most likely to carry West Nile virus. When a Chaska yard still has heavy biting pressure after the containers are gone, owners typically bring in a privately licensed applicator for barrier treatments on shrubs and other shaded resting spots. MMCD itself points residents to the Minnesota Department of Agriculture license lookup for that.

Wasps, yellowjackets and Chaska brick

University of Minnesota Extension describes yellowjackets as nesting in old rodent burrows in the ground and in cavities such as hollow logs, landscape timbers, attics and wall voids, while baldfaced hornets hang papery nests from trees and eaves. Paper wasps build single, uncovered combs under horizontal surfaces such as eaves, beams, garage rafters and sheds. Nests are started from scratch by a queen in April or May and can hold hundreds to thousands of yellowjackets by late summer, when Extension notes some species turn into aggressive scavengers around outdoor food and may sting without provocation.

Old masonry is part of the Chaska picture. The city’s Maintenance & Repair Guide for Designated Historic Residences explains that brick buildings put up before 1900 used a soft, high-lime mortar that gradually erodes as water runs over it, and it recommends repointing joints that are loose, crumbling or recessed more than half an inch. An eroded joint, a gap around a window frame or a loose piece of trim is the kind of opening that leads into a wall cavity — and in fall, Extension notes, newly mated queens look for sheltered spots to spend the winter, including inside buildings under siding. That is why wasps that turn up indoors in late winter or early spring are usually queens emerging from winter shelter, not proof of an active nest in the house.

Extension’s guidance on nests inside a structure is specific: hidden yellowjacket nests in wall voids, attics or concrete block are much harder to control than exposed ones, and Extension generally recommends having a pest management professional deal with them. Spraying an aerosol into the entrance often fails and can push the insects to find another way out — sometimes into the house. Above all, do not seal the entrance until every yellowjacket is dead. Anyone who is allergic to stings should not try to handle a nest at all.

When the wasp repair touches a historic building

Chaska’s Heritage Preservation ordinance (City Code Chapter 10.5) created a Heritage Preservation Commission to look after historic properties and districts, and exterior work on a designated resource or inside the historic district generally needs a Site Alteration Permit. The practical order of operations for a wasp problem in an old brick wall is therefore: get the nest dealt with first, then close up the opening properly.

The city’s maintenance guide lists several jobs as minor classes of work that typically skip a full HPC hearing but are still reviewed by the HPC liaison, including caulking and weather stripping and repointing when the new mortar matches the original in color and composition. It stresses that mortar should be softer than the brick so the wall can expand and contract without cracking, warns against high-speed grinders that damage the bricks, and says sandblasting should never be used on a brick building. For questions about minor work, the guide gives the city’s number, (952) 448-9200, and says to ask for the City Planner. A licensed exterminator can remove the nest; a mason experienced with historic brick handles the mortar.

Bees in the wall are a different call

Not every stinging insect in a Chaska wall is a wasp. Extension notes that honey bees occasionally nest in wall voids, and that the first step is getting a sample or clear photo identified; confirmed honey bee colonies are a job for a beekeeper where possible, and the University’s Bee Lab points Twin Cities residents to the Minnesota Hobby Beekeepers Association. Bumble bees sometimes nest in siding or wall cavities too, and Extension cautions that the rusty patched bumble bee is listed as endangered under the Endangered Species Act, so its nests may not be destroyed without a permit. When Exterminator Dispatch routes a stinging-insect call, it helps to say what the insects look like and where they are going in.

Timing matters as well. Extension says yellowjacket and paper wasp colonies do not survive a Minnesota winter, even inside a building, and that freezing temperatures in the mid to upper 20s F kill the old queen and the workers. A nest high under an eave that nobody walks past can sometimes be left to the first hard freeze; a nest by a door, a deck or a play area usually cannot.

Other calls from Chaska homes

Chaska is not only historic brick. The city credits the Jonathan New Town concept, introduced in 1966, with bringing new land and residents, and its history page says residential construction adds 100 to 300 new homes per year. Newer houses bring their own entry points: utility penetrations, siding seams and garage door gaps that let in mice when the weather turns and boxelder bugs looking for a sunny wall. Extension recommends finishing exterior repairs for boxelder bugs before the end of August. It also treats carpenter ants as a problem that usually warrants a pest management professional to locate and eliminate the nest, and describes termites as uncommon in Minnesota and generally limited to the southern part of the state, so a suspected termite find in Chaska should be identified before anyone recommends treatment.

ZIP codes served

Chaska City Hall’s mailing address uses ZIP code 55318. Requests from surrounding Carver County communities are routed to licensed companies that already cover those addresses.

Verifying that a Chaska exterminator is actually licensed

In Minnesota, the people usually called exterminators are structural pest control applicators, and the Minnesota Department of Agriculture does not allow them to apply pesticides commercially without a valid license. The MDA issues structural licenses at three levels — Company, Master and Journeyman. Individual applicators must work under a licensed Structural Pest Control Company, and each licensed company must employ at least one licensed Master, supply workers’ compensation information and meet the state’s financial responsibility requirements.

Yard mosquito spraying is covered by a separate category. MMCD’s guide tells residents to search the MDA database by county under the license type “Commercial Pesticide Applicator – Mosquitoes, Black Flies, and Ticks.” Before work starts on a Chaska property, ask for both the company name and the applicator’s name and look each one up in the MDA’s online license search. Exterminator Dispatch expects every company it routes to hold the correct Minnesota license for the job, but the check takes only a few minutes.