The Pest Season Is Getting Longer: State Warming Since 1990

The pest season getting longer is one of those claims the industry repeats without a number attached. There is a number, it is published free by NOAA, and it says something more specific than the general claim: the change is concentrated in winter, and concentrated in the north east.

What changed, and by how much

We compared two ten-year averages of statewide temperature: 1991 to 2000 against 2016 to 2025. Using decades rather than single years removes most of the year-to-year noise, and a 25-year gap is roughly the working life of a pest control business.

Every one of the 48 contiguous states is warmer on an annual basis. The increase averages 1.56 degrees and runs from 2.04 degrees in New Jersey down to 0.82 degrees in Washington. The geography is consistent: the north east and mid-Atlantic warmed most, the Pacific north west and northern Rockies least.

Change in average temperature in degrees Fahrenheit, 1991 to 2000 compared with 2016 to 2025. Winter is December, January and February.

Winter is where the change matters

Annual average temperature is the wrong measure for pest pressure. What limits how far north many pests survive, and how many survive to spring, is winter cold, and winter has moved differently from the year as a whole.

Nationally, winter warmed 1.20 degrees, less than the annual figure. That average hides a split. Thirty-nine of the 48 states had warmer winters, and in the north east the winter change is substantially larger than the annual change. Maine warmed 1.92 degrees on the year and 2.98 degrees in winter, moving its December to February average from 17.8 to 20.8 degrees. Vermont, New Hampshire, New York, Massachusetts, Rhode Island, Connecticut and Michigan all show the same pattern.

Nine states went the other way in winter: Kansas, Oregon, Colorado, Idaho, Washington, Wyoming, South Dakota, Montana and Nebraska, all by less than half a degree. These are small changes and we would not read much into them individually, but they are a useful corrective to the idea that everywhere is warming uniformly.

What a warmer winter does and does not tell you

A three-degree rise in the winter mean is not the same as a three-degree rise in the annual minimum, and it is the extreme cold nights, not the average, that determine overwintering survival for most insects. A state can warm on average while still delivering the cold snap that kills. The honest reading of this data is that it establishes the direction and the regional pattern, and that it is consistent with a longer active season, rather than that it proves any particular species has moved.

Where the evidence is stronger is in the specific range expansions that have been documented independently: the northward movement of ticks covered in our work on the Asian longhorned tick, and the establishment of species such as the Joro spider and spotted lanternfly outside their original ranges. Temperature is one driver among several there, alongside trade and transport.

The operational overlap nobody has connected

The states with the largest winter warming are the same states with the most seasonal businesses. Our analysis of employment by month found the biggest peak-to-trough swings in the northern tier, where a third of the workforce is not on the payroll in February, against almost no swing in Hawaii and Florida.

That is the commercial question buried in the climate data. A northern operator whose business model assumes a dead January is running on an assumption about winter that has moved measurably in 25 years. It has not moved enough to make the north look like the south, and nothing here suggests a northern market can be run as a year-round one on temperature alone. It has moved enough that the shoulder weeks at either end of the season are worth measuring rather than assuming, and rodent work, which is driven by pests moving indoors rather than by outdoor activity, has always been less seasonal than the overall employment swing implies.

How we did this

Data comes from NOAA’s National Centers for Environmental Information statewide time series, which reconstructs average temperature for each state back to 1895 from the weather station network. We took the arithmetic mean of annual average temperature for 1991 to 2000 and for 2016 to 2025, and the same for the December to February winter season, then took the difference. Alaska and Hawaii are excluded because the contiguous series is methodologically consistent and theirs is handled separately.

This is a descriptive comparison of two periods, not a trend model, and it makes no attribution claim about cause. Ten-year averages reduce but do not remove the influence of individual extreme years at either end.

Frequently asked questions

Is the pest season getting longer?

The temperature data is consistent with it. All 48 contiguous states are warmer than in the 1990s, by 1.56 degrees Fahrenheit on average, and winter has warmed 1.20 degrees. Whether that translates into a longer active season for any given pest depends on extreme cold nights rather than averages, so the data establishes direction rather than proving a season length.

Which state has warmed the most?

On annual average temperature, New Jersey, at 2.04 degrees Fahrenheit between the 1990s and the last decade. In winter, which matters more for pest survival, Maine leads at 2.98 degrees, followed by Vermont at 2.85 and New Hampshire at 2.56.

Does a warmer winter mean more pests?

Not directly. Overwintering survival depends on how cold the coldest nights get, and a state can raise its winter average while still producing a hard freeze. Warmer winters make a longer active season more likely, and documented range expansions in ticks and several invasive insects are consistent with that, but temperature is one factor alongside trade, transport and habitat.

Are any states getting colder?

None on an annual basis. In winter, nine states are marginally colder than in the 1990s: Kansas, Oregon, Colorado, Idaho, Washington, Wyoming, South Dakota, Montana and Nebraska, all by less than half a degree Fahrenheit. These are small differences over a 25-year gap.

Sources

• NOAA National Centers for Environmental Information, Climate at a Glance statewide time series, annual and December to February averages, 1991 to 2025. ncei.noaa.gov
• Analysis by The Pest Control Brief, September 2026.