Mosquitoes may be the absolute worst organism inhabiting Earth today. Setting aside the garden-variety aggravation of billions of mosquito bites each year, the bugs are vectors of horrible diseases that kill literally hundreds of thousands of people annually.
We’ve all become acutely aware of this latter point with the sudden rise of the Zika virus, which is linked to birth defects and is now inching its way north through the Americas on the backs of several mosquito species. Given that it’s now late May and what is colloquially known as “mosquito season” is underway, concern over the virus and the bugs that carry it is mounting.
When exactly is mosquito season, though? There’s no easy answer to this. According to the American Mosquito Control Association (heroes!), there are 176 mosquito species active in the states. They all have slightly different life cycles and become active under various conditions (some hibernate over winter, others lay eggs that hatch in the spring).
But at some point every year, we all have that experience of going outside one evening and feeling that first piercing itch or hearing that first high-pitched drone, and we know that this season’s War On Mosquitoes has officially begun.
One way to quantify the seasonal changes in mosquito activity is to look at Google search data. After all, when the bugs start biting, people tend to hit the computer to look up good repellents, itch remedies, preventative measures and the like.
In the chart below, I’ve taken Google search data for 2014 and 2015 and averaged them together to get a typical, composite year of search interest in mosquitoes in the United States.
As you can see, people start searching for mosquito stuff in the spring, and interest shoots up rapidly through May, reaching a small peak in late May. Then interest explodes again through June, putting the annual peak in interest at almost exactly halfway through the year. From July, the numbers show a steady decline in interest all the way through until winter.
I should stress that although these numbers almost certainly correlate with actual mosquito activity, they’re probably not a perfect match. People could be searching for mosquitoes for reasons completely unrelated to whether their back yard is currently a bug-ridden hellscape — for instance, they could be students doing research, or people planning next year’s garden, or what have you.
Still there’s good reason to believe that this is a pretty good barometer of mosquito activity. Google’s data shows the top search topic related to “mosquito” is “itch - symptom.” Other related queries include “mosquito bite,” “mosquito repellent” and “mosquito spray.”
Of course, the biggest weakness with national-level data is that ours is a big country, encompassing many different environments, and mosquitoes are very likely to become active at different times in different places. One way to tease this out would be to look at the same data as in the chart above, but do it for each of the 50 states.
That’s what the cartogram below shows — each state has a mini-chart showing search interest in mosquitoes over the course of a typical year (2014-2015 average).
There's an interesting geographic pattern here. In dry states in the mountains and plains (the Dakotas, Nebraska, Wyoming and others), there's a sharp burst of mosquito search activity in the middle of the summer and then little interest the rest of the year.
But in places like the Gulf Coast states and elsewhere in the South, the annual curve is more rounded, suggesting a certain baseline level of mosquito activity all year round.
Others don’t follow a typical pattern. In Arizona, for instance, interest peaks in October, rather than the middle of the year.
Keep in mind that the actual magnitude of search interest conveyed here isn’t comparable between states. That’s because some states are a lot more interested in mosquitoes than others. The biggest mosquito-searching states are Alaska and Hawaii, according to Google. If I had set all of these charts to the same scale, the high volume of interest in Alaska and Hawaii would make for much flatter charts everywhere else.
Still, the Google search data may prove to be useful to public health authorities looking to mitigate exposure to mosquitoes in the coming months.
Correction: In a previous version of this story, the data for states after D.C. alphabetically were incorrect. The map and analysis have been updated to reflect the correct data and geographic patterns.