[Cover Story] On the Move

Features - Cover Story

Insects that are pushing their ecological boundaries are telling us, yes, the world is getting slightly warmer. What does this mean for your pest management firm?

March 19, 2014
Kristen Hampshire

Pests are crossing state lines and exploring territory that generations before them considered too cold, too dry, too wet. Invasive pests are hopping a flight to our cities, too, and they’re settling in just fine thanks to our warmer winters.

Meanwhile, extreme storms blow insects up and away from their balmy territories, carrying them north and every which way. They get a free ride to a higher latitude.

What’s climate change got to do with it? Some insects are pushing their ecological limits, and they’re adapting and hanging in there.

The fact is, our world is a warmer place today than it was 30 years ago. Climate change is happening, and we’re not talking about isolated weather events like a scorching summer or this winter’s Polar Vortex. The gradual warming of the Earth over decades, hundreds of years, is evident in climatology reports, and the effect on insect and rodent populations is real.

“The scientific evidence for a global rise in temperature over the past few decades is really quite convincing, and the scientific evidence that insects and plants are responding to this change is irrefutable,” says Coby Schal, urban entomologist at North Carolina State University.

Studies of termite movement, mosquito activity, ant colony development and rodent behavior show that even the tiniest temperature bump — if sustained, as climate change infers — can prompt developmental and behavioral changes in species, such as the foundation of new colonies.

Rodent Recovery from the Polar Vortex

“Warm” is not exactly a word that came to mind in January 2014, when the Polar Vortex blew in and frosted the map with below-zero temperatures. But this is an “event,” a blip on the long-term climate radar. Climate change is viewed over 100-plus years. The gradual warming trend is bound to have interruptions.

But even the Polar Vortex didn’t kill off some motivated rodents. Dr. Robert Corrigan, an urban rodentologist with the New York City Department of Health and Mental Hygiene, was out in the coldest nights of the vortex in early January, watching park rats make the rounds through the snow from their burrows to litter baskets in search of food. “The snow cover was full of rat tails,” he reports.

Here, Corrigan makes a few key points about severe winter and rodents:

  • Severe cold snaps have to be prolonged (a few weeks) to have a long-lasting impact on exterior rats.
  • It takes about a year to make a full recovery to the original population level (providing resources remain the same) following a winter kill.
  • Rats can recover in as quickly as six months when control programs are performed in warm-weather months (April to September).

“Insects are sort of like a canary in a coal mine,” says Mike Potter, professor of entomology at the University of Kentucky. “They sometimes reveal subtle changes in the environment through their abundance and distribution.”

To be sure, global climate change is a subtle thing — we’re talking a gradual century-long increase in temperature by about 1.3°F, according to a Climate Central report of continental U.S. warming. To make matters more complicated, some states have warmed more, some less and others not at all. (Check out the chart on page 34.)

Still, when the Intergovernmental Panel on Climate Change (IPCC) released its predictions for worldwide climate change for the next 100 years, it reported that most of North America will become warmer and many parts will become wetter. IPCC notes the first “greenness” in the North American spring has come 10 to 14 days earlier since 1981.

Sure, the temperature rise is oh-so-slight. But that minute increase over time is enough to sustain insect and rodent populations and entice migration beyond typical latitudes. Or, when winds from extreme weather events carry pests to new places, they adapt because the climate where they’re dropped is warm and/or wet enough to sustain them.

Do you “believe” in climate change? Scientists are uncovering evidence that it’s happening. Maybe global warming is not rocking your world or changing your business strategy today. But it’s there, on the radar, and climate change, in conjunction with weather patterns we experience on an annual basis, means some new “house” rules regarding where pests live, and why.

“Insects make for great evidence for climate change,” Schal affirms. “We are seeing insects that used to be restricted to certain latitudes move up to much higher latitudes, to previously colder areas.”

Climate or Weather?

Bah — climate change is for the politicians. It’s a hoax. (Did your furnace turn off in January 2014?) It’s environmentalist hoo-ha. If this is what you’re thinking, you’ve got company.

True, the term “climate change” carries a load of political baggage. In our turbulent legislative environment, climate change is practically a partisan issue. So it’s no wonder that some want to back away from associating climate change with pest activity. But, scientists studying research and climatologists reporting weather statistics are working off of data — and the numbers are pretty tough to argue.

“I think so many people are confused by this topic because we pay too much attention to what politicians are doing,” Schal acknowledges. “If we only paid attention to the scientists, it’s really quite convincing. And you know, the important thing is not to pay attention as much to the individual seasons, but to look at the average weather pattern that is going on, and that is pretty clear.”

Climate change is not about that record high heat that Ohio experienced for a week in July, or the balmy February weekend folks in Illinois enjoyed. Nor is it about the monsoon conditions one summer, or this year’s Polar Vortex.

Understanding what climate change is matters to the debate, which if you consult with scientists, is no debate at all. The question entomologists consider is not whether climate change exists, but rather how does it affect insects and rodents?

As some entomologists study the movement of insects to different areas, they’re finding an association between gradual warming of global temperatures and insect activity.

Why does this matter? For one, the spread of insect and rodent populations to regions that are unprepared to control them can result in disease. Look at West Nile virus. “That should be a wake-up call for all of us, and there are nastier diseases than that that are a one-day plane flight away from us,” says Joe Conlon, technical adviser to the American Mosquito Control Association (AMCA). Travel and tourism introduces pests to the United States, and those tropical species can survive in warmer temperatures that many urban environments here offer.

Climate change should be on the radar of PMPs who need to stay current, even if the gradual warming means that there will be no real threat in the lifetime of their companies. “As an industry, we realize we are supposed to be protectors of the public’s health, and there clearly could be a relationship between these large, global temperature changes and the pests that we make our living fighting,” Potter says.

PCT readers who responded to our State of the Industry survey do express a concern for global climate change (see charts below).

Climate change is a long-term factor — and none of this is to say that gradual warming affects pest populations more than annual weather trends. What’s happening right here, right now is the top priority for pest management professionals, says Grayson Brown, director of the public health entomology laboratory at the University of Kentucky.

In other words, there’s climate — and there’s weather.


“I’m most concerned with tracking the insect populations that are present at any given time and trying to understand them to be where they are,” Brown says, adding that in his 40 years as an entomologist, the only constant is change. “Every year, something is different, and PMPs will say the same thing,” he says. “Insect populations have always been dynamic.”

Pests Respond to Climate.

“Cities are a good predictor of climate change,” says Grzegorz Buczkowski, who heads the urban ecology laboratory at Purdue University’s Entomology Department. He has been observing ant colonies in the forest and urban environments, specifically studying a “super colony” of ants on the Purdue campus.

In a 200-by-200 yard colony, there are hundreds of nests connected by trails with an estimated 500 million workers and 50,000 queens. Just a half-mile away in the forest site, there is a single queen and colonies with 50 to 100 workers.

Essentially, his work shows that ants are moving into cities and thriving there for several reasons. For one, there are more resources (food, nesting sites) in urban settings. “In the forest, there is more competition for resources because there is more ant diversity,” Buczkowski says. With more ant species in the forest, there’s competition for life-sustaining necessities.

“Climate change could be one factor,” Buczkowski says, relating that cities are 2 to 3 degrees warmer because of the “island” effect. (Parking lots and buildings heat up cities and hold the heat in.)

This warm island effect is also an explanation for how insects may travel from warmer climates farther north, hopping from one city environment to the next.

So with urbanization and deforestation to build cities, there are more warm islands, Buczkowski says. And, with more cities come more warm pit-stops or permanent residents for insects. “It seems that ants benefit from living in the city,” he says. “Cities are good overwintering sites.” (His work looks at odorous house ants.)

Also interesting, a move into the city (so to speak), resulted in less diversification of ant species. “Not all ants will survive in the city — so you go from 28 species to roughly 18,” Buczkowski observed.

What we do know from this research is ants are adapting to the human environment. They want to hang out with us. We give them food, warm places to live and an opportunity to thrive in the winter — those few degrees make every bit of difference. “Ants that normally occur in the wild have adapted and are moving to the human environment, so they have changed their biology to be around humans,” Schal says of the study’s findings.

Ants aren’t the only ones taking to warmer temperatures. And we’re talking the subtle, slight uptick on the thermometer, Potter says. “Small elevations in temperatures over many years drives reproduction,” he says.

Mosquitoes are a real problem, and they seem to be multiplying depending on when and where you study them. Weather, and climate, play a critical role in this. “It’s a well-known fact that mosquito reproduction falls in line with weather patterns: wind direction, precipitation patterns, temperature fluctuation — this all affects mosquito control,” Conlon says.

Increased travel and tourism certainly influence the activity of mosquitoes and insects, in general, Conlon says. “I think we are only seeing the tip of the iceberg in terms of invasive species…We have plenty of mosquitoes here already that are fully capable — in the lab, at least — of transmitting a number of exotic mosquito-borne diseases. All we need is a host to get here.”

Conlon adds of mosquito control on a municipal level: “Complacency kills.”

Diseases like malaria and yellow fever actually used to be quite prevalent in the United States. “They could be again if we let our guard down, which is one of the most visible tasks in the vector control profession: to keep the public aware that just because you don’t have West Nile virus in your area now doesn’t mean it can’t get there. And just because you live in Minnesota or Manitoba does not mean these mosquitoes can’t invade.”

Take Alaska — not exactly a climate you’d associate with swarming pests. But mosquito problems in Alaska during summer are rivaled only by the Everglades, Conlon says. “There are documented cases of caribou being asphyxiated by mosquitoes because they are so bad up there,” he says. The mosquitoes emerge from the tundra in staggering numbers if they find a host to take advantage of, at the rate of 5,000 bites per minute, Conlon says. “It’s just really bad.”

Meanwhile, Conlon will field a phone call from a homeowner living on an island in the Georgia salt marshes who wants to know why his mosquito problem is so bad. (“I can’t enjoy my pool,” he complains.) “At present, we are moving into places where mosquitoes are, so we are more aware of them,” Conlon explains. So, there is insect evolution—and the evolution of people’s desire to live in insects’ traditionally “exclusive” habitats.

Jim McNelly is director of mosquito control for Volusia County, Fla. His office was founded 77 years ago specifically to manage salt marsh mosquitoes. “We are seeing a resurgence of mosquito species that reproduce in containers, both manmade and natural,” he says, referring to buckets, tree holes, etc.

The species he’s finding are Aedes aegypti and Aedes albopictus. Droves are camping out in backyards — a real nuisance that homeowners are willing to pay for in order to eradicate. Aedes albopictus was introduced to the U.S. in 1985 in Texas, and spread from there, arriving in Volusia County in 1992 — a slow creep. “The majority of service calls and requests we get are for those species that live in your backyard,” McNelly says.

Disease potential is a concern. “The aegypti drove the dengue [fever] outbreak in the Florida Keys several years ago, and this past season there was an outbreak in St. Lucie County, also attributed to the aegypti,” McNelly says. McNelly thinks that climate change is allowing the expansion of these species that impact our daily operations.

Potter adds: “Climate change is also associated with extreme weather events like flooding, heavy rainfall and drought, and slight increases in the elevation of water. Basically, water and stagnancy equals good mosquito breeding conditions.”

The Pied Piper Effect.

How do insects make their way to new environments where they might not have thrived in the past? And, how fast does this happen?

That all depends, Schal says. An insect that is pre-adapted to “moving up” may take hold in a region rather quickly. For example, say an invasive insect native to a cold region in Japan is introduced to the southeast U.S. “Slowly, that insect is moving north and it is pre-adapted, having evolved in Japan in a cold climate,” Schal says, illustrating one scenario.

“If the insect is native and restricted to the Southeast, it may take many generations for that insect to evolve to be able to cope with colder environments,” Schal continues. “But, if as colder regions become warmer, it doesn’t have to do a whole lot of changing at all — all it has to do is move up north.”

Insects are expert environmental trackers. “Climate change can expand their ecological range,” Schal says. It’s a pied piper effect.

Say an insect moves north, and then a weather event like this year’s Polar Vortex occurs. Sure, this cold spell will kill off insects that moved north because of global change, Schal says.

But a cold, wet or dry episode might not keep the pest away for long. “In one or two years, it could be back depending on what the following summers and winters look like,” Schal says.

Timing is everything for creating a welcome environment to usher insects “up” from southern states. That is, moisture patterns are affected in spring and summer, and temperatures are affected in winter and spring. In particular, warmer winter temperatures help insects and rodents “last” through the bleak months, says Robert Corrigan, an urban rodentologist at the New York City Department of Health and Mental Hygiene.

Rodent control business for pest management firms has increased due to repeating mild winters, Corrigan says. Where rodent control used to be a business that “popped” in the fall when mice and rats typically move indoors, now it’s a year-round service. “With repeating mild winters, rodents can increase their numbers of offspring because the winter doesn’t threaten reproduction,” he explains.

Brown says climate change aside, fluctuating and warmer winter/spring temperatures on a year-to-year basis are driving new insect activity. “A few degrees difference, one way or the other, makes a big difference in the development rate of insects, and that is why after a warm spring, we will often see more insects than normal,” he says.

Moisture is generally a limiting factor for insect populations when rainfall occurs in late summer. “A lot of populations are evolved to do well in dry conditions, and if it stays rainy in late summer, they don’t do well,” he says. The opposite is true for insects evolved to thrive in wet environments.

Last year, in many areas, rain continued all summer and mosquitoes were biting more than usual. But the type of mosquitoes that spread West Nile prefer standing, stagnant water, and the constant rain ensured “fresh” puddles that do not attract this type of insect.

We know that weather happening right now is what drives business in the door as conditions affect pest pressure. And with gradual warming, regions that never enjoyed the company of certain insects — for example, termites currently don’t bother the Upper Peninsula of Michigan — might move up with little adaptation, bringing with them new control issues.

What’s a PMP to do about all of this?

Just be aware of weather patterns over the long-term and understand how climate change might impact pest pressure over time. “I wouldn’t be worried about climate change itself as much as I would be worried about what has been happening the last couple of years with weather, and do I have the tools to deal with it,” Brown says.

Concerning mosquitoes, with their increased presence, and perhaps fewer government-funded control programs to manage the insects, there will be a greater reliance on PMPs to fill the gap, Conlon suggests.

Overall, PMPs should continue ongoing training, Brown says. “They need to get their CEUs and keep updated on entomological knowledge. Because every year, there is something new out there.”


The author is a frequent contributor to PCT magazine. She can be reached at khampshire@giemedia.com.