Overview

Winter 2023-2024 has been the warmest on record and the expectation is for that trend to continue with warmer than average spring months for much of the country. Most pests live a significant portion of their lives outdoors and pest populations are often positively correlated with increased temperatures, fewer freeze events, and normal to high levels of precipitation. What does this mean to you? We may be in for heavier than typical pest pressure for the rest of the year if weather predictions hold. Forecasting pests is even more complicated than forecasted weather, though. There are many factors to consider: Population sizes over the previous years, availability of food, predator numbers, etc.

Rodent populations can also fluctuate depending on exterior environmental factors, but the effects are often longer term and can be overshadowed by the close association they have with human activity, infrastructure. An interesting phenomenon with commensal rodents (house mouse, roof rat, Norway rat), is that often when one species surges the other two species seem to decline in severity. Norway rats, although found throughout the U.S., now only cause spotty and dispersed pest issues. This is a significant decline in activity over the past few decades due primarily to the expanding roof rat invasion on this continent. Commensal rodent trends in this report are based on customer calls, catch trends, and general activity patterns. These trends in this study focus on activity in commercial structures.

New England and Northeastern U.S.

New England and the northeastern United States experienced higher winter temperatures and the expectation is that spring will be much the same. This may translate to earlier and more active ant colonies, bringing foraging workers in and around your facilities as they search for food to grow and help sustain their colonies. Early inspection and treatment for ants is recommended to suppress or eliminate colonies before they rapidly grow and become even more of a nuisance. 

Meteorologists have forecasted above average rainfall for the region which could, in combination with higher temperatures, lead to higher numbers of both mosquitoes and large flies. For mosquitoes, it’s essential to remove as many sources of standing water as possible from around your building to disrupt their life cycle and prevent mass emergences of adults that bite and could potentially vector disease. 

Ecolab’s Large Fly Program uses an outside-in strategy to focus on eliminating flies and the conditions that support them from the outside where they are breeding to reduce populations and therefore, the number of flies that could make it indoors and cause problems. What can you do to help? Step up exclusion efforts by keeping doors and windows shut or tightly screened while paying close attention to how trash and recycling are handled throughout your facility. Trash and recycling bins, including dumpsters, should be emptied frequently and cleaned to prevent fly attraction and development. 

Ticks are a major public health concern in this region due primarily to the prevalence of Lyme disease. Providing education to your employees/teams about the risks of ticks and how to be tick-safe is valuable, even if your facility presents a very low risk of tick populations. Facilities that have grounds or areas that abut ecotones or tall grass/forests area do carry risks of ticks and deserve management considerations.

When it comes to commensal rodents, mice continue to be the predominant pain point in the northeast. Taking advantage of old infrastructure and stable human populations, mice have entrenched themselves in cities and aggressively invade human spaces. They will continue to be a challenge with some populations rivaling rats in their tenacity and survivability.

Midwest/OH Valley/Great Lakes

The Midwest and Ohio Valley regions also experienced a warm winter coupled with, in some places, way below average snowfall and rainfall. Entering a warmer, drier spring than usual could see moisture-seeking pests like ants aggressively foraging and even nesting indoors when they find a good, consistent source of moisture. Early inspection and treatment for ants is recommended to suppress or eliminate colonies before they rapidly grow and become even more of a nuisance. This could also be true for occasional invaders which typically live on the exterior perimeter and are associated with mulch and leaf litter – Think earwigs, springtails, pillbugs, and millipedes. If there is insufficient moisture in their normal environment, they will follow moisture gradients toward and into buildings.

A mild winter may have also led to greater numbers of surviving overwintering pests like wasp queens, multi-colored Asian lady beetles, brown marmorated stink bugs, boxelder bugs, and cluster flies. If more of these pests were able to survive the winter, we should anticipate greater numbers of their populations the rest of the year. This may be a bad year for yellowjackets, paper wasps, and baldfaced hornets and proactive inspection and treatment should be prioritized to tamp down numbers and help protect your employees and guests during the late spring through fall. For all those other overwintering groups, we may not truly feel the effect of elevated numbers until they begin gathering en masse to overwinter indoors in late summer to early fall. Efforts to exclude these pests should begin in early summertime and wrap up prior to August, for best results.

Mouse pressure is high continuing down the coast and begins switching to strong roof rat pressure towards the Carolinas with roof rat hot spots in Virginia and South Carolina, and areas of mixed rodent activity in some locations. Moving away from the coast into the Midwest, mice remain the predominant species although lessening in pressure. This pattern is expected to continue with roof rats slowly expanding their influence northwards along the coast.

North Central and Plans

North Central and Plains region had a relatively similar winter and upcoming forecast as the Midwest and Ohio Valley regions: Warm winter coupled with, in some places, way below average snowfall and rainfall. Entering a warmer, drier spring than usual could see moisture-seeking pests like ants aggressively foraging and even nesting indoors when they find a good, consistent source of moisture. This could also be true for occasional invaders which typically live on the exterior perimeter and are associated with mulch and leaf litter – Think earwigs, springtails, pillbugs, and millipedes. If there is insufficient moisture in their normal environment, they will follow moisture gradients toward and into buildings.

A mild winter may have also led to greater numbers of surviving overwintering pests like wasp queens, multi-colored Asian lady beetles, brown marmorated stink bugs, boxelder bugs, and cluster flies. If more of these pests were able to survive the winter, we should anticipate greater numbers of their populations the rest of the year. This may be a bad year for yellowjackets, paper wasps, and baldfaced hornets and proactive inspection and treatment should be prioritized to tamp down numbers and help protect your employees and guests during the late spring through fall. For all those other overwintering groups, we may not truly feel the effect of elevated numbers until they begin gathering en masse to overwinter indoors in late summer to early fall. Efforts to exclude these pests should begin in early summertime and wrap up prior to August, for best results.

Rodents, and rats in particular, may also be more drawn to structures and the periphery when in search of consistent food and water. The best defense against rodents is to make your facility as impenetrable as possible by installing rodent-resistant door sweeps, fixing holes and gaps, trimming vegetation away from the building, and being thoughtful about how trash and recycling are stored and dealt with.

A surprising increase in mouse activity is found in commercial structures in north central areas of the US. Mild winter in these areas may contribute to the continuation of this trend.

Southeast and South-Central

Spring is well underway in the south-central region of the US with warm temperatures and heavy rains. When you combine the two you get a perfect recipe for flies and mosquitoes. Standing water is the key to mosquito development so it’s essential to remove as many sources of standing water as possible from around your building to disrupt their life cycle and prevent mass emergences of adults that bite and could potentially vector disease. Keep in mind that a miniscule amount of water, like a bottle cap’s worth, can yield mosquitoes.

Large flies (house flies, flesh flies, bottle/blow flies) are highly mobile and rapid reproducers that thrive in warm and wet conditions and the expectation is that this spring and summer will provide exactly what they need. Ecolab’s Large Fly Program uses an outside-in strategy to focus on eliminating flies and the conditions that support them from the outside where they are breeding to reduce populations and therefore, the number of flies that could make it indoors and cause problems. What can you do to help? Step up exclusion efforts by keeping doors and windows shut or tightly screened while paying close attention to how trash and recycling are handled throughout your facility. Trash and recycling bins, including dumpsters, should be emptied frequently and cleaned to prevent fly attraction and development.

Roof rats dominate the south in Florida and from Georgia through Louisiana. Although the warm temperatures allow for healthy populations, these pest populations seem stable, without significant change forecasted. A mix of rodents is found to the north with mouse hot spots in Arkansas and eastern Tennessee, and roof rats in western Tennessee. It is difficult to predict how far north roof rats will be able to gain a foothold, but certainly an important watch-point.

Southwest

The Southwest is predicted to have a warmer, drier spring than usual could see moisture-seeking pests like ants aggressively foraging and even nesting indoors when they find a good, consistent source of moisture. Early inspection and treatment for ants is recommended to suppress or eliminate colonies before they rapidly grow and become even more of a nuisance. This could also be true for occasional invaders which typically live on the exterior perimeter and are associated with mulch and leaf litter – Think earwigs, springtails, pillbugs, and millipedes. If there is insufficient moisture in their normal environment, they will follow moisture gradients toward and into buildings.

Norway rats, roof rats, and other rodents may also have stronger affinity to your grounds and structures in search of consistent food and water and nearby nesting sites. The best defense against rodents is to make your facility as impenetrable as possible by installing rodent-resistant door sweeps, fixing holes and gaps, trimming vegetation away from the building, and being thoughtful about how trash and recycling are stored and dealt with. Fruit and seed-producing plants on property also deserve careful consideration since they can attract and support rodents as well as birds, stinging insects, ants, flies, and other pests.

Roof rats continue to present sever pressure in Texas. This is likely the hottest spot for this pest in the US. This pressure will continue. Over the past 20 years roof rats have been introduced and expanded in central Arizona and Los Vegas Nevada. These rats could not survive in the deserts of the southwest, but human infrastructures, exterior food (legumes, dates, oranges, etc.) and watered landscaping have created a perfect niche for their invasion and continued proliferation. The theme of roof rats continues along the west coast northward through California. Moving north from the southwestern states, mice become the predominant pest with stable populations and local hot spots.

Northwest

Above-average winter temperatures coupled with a rainy start to spring in the Pacific Northwest are going to be good for stinging insects, carpenter ants, mosquitoes, ticks, and flies.   

Carpenter ant swarms are already underway in some parts of this region and deserve attention since these pests are destructive and not at all inconspicuous. Locating carpenter ant nests is the key to eliminating colonies and it takes true expertise to do so.

Roof rats continue to be the rodent of concern along the west coast northward. This pest continues to take advantage of human infrastructure to progress along the entire coast. This trend will continue with mice found inland and rats progressing along the coast.