Prenolepis imparis

School of Ants collection
Literature record

Prenolepis imparis

From Dr. Eleanor's Book of Common Ants

A.K.A.: Winter ant or false honey ant

Size: Workers 0.1-0.14 in; queen 0.32 in; males 0.11-0.15 in

Where it lives: Winter ants nest deep in the soil near tree bases or in open ground, like lawns.

What it eats: While winter ants won’t pass up on the opportunity for a sugary snack, these ladies prefer protein-packed food, noshing on other insects unlucky enough to endure winter’s chill.

What’s the big deal?

Remember in Alice in Wonderland when Alice followed the white rabbit down its bunny hole? The hole was ordinary enough at first, but once Alice climbed in, she fell down and down until she came to a completely different world. Holes like that rabbit’s pepper the ground across the United States. If we were as small as ants, we could tumble repeatedly down into other worlds. Winter ants (Prenolepis imparis) are the white rabbits of ants. Plunging down their holes gives us a peek into their truly extraordinary lives.

Unless you follow a winter ant home, its nest’s entrance can be hard to find. About the size of a buttonhole winter ant nests aren’t a lot to look at on the outside. Inside, deep mazes of tunnels connect chambers all the way to the bottom. They can extend almost 12 feet deep in the soil (Tschinkel 1986). That would be the human equivalent of a class of second graders digging a hole more than 1.14 miles down, deep enough that 150 school busses could be stacked end-on-end before reaching the surface.

All that depth serves a purpose. While most ants are active in the spring and summer, winter ants are active in the fall and winter. Soil temperatures do not vary as wildly as the temperature above ground, so when winter’s chill plummets the air to 33°F, the winter ant’s nest is kept insulated by the earth at a balmy 64-68°F. This heat is important because between 40-50°F, most insects have a serious case of freeze brain, going into what bug people call a “chill coma,” where their muscles stop working so they can’t move (Rust and Reierson 1997). Underground, winter ants beat the ice. Above ground, they dig short “warming tunnels” scattered around their nest. When they start to get cold walking around outside, they run down into the tunnel and warm up (Tschinkel 1986).

Staying out of trouble

My mother always told me the best way to stay out of trouble is to avoid it. Winter ants are masters at avoiding trouble because they are active when trouble is fast asleep (Tschinkel 1986, Holway 1998, Lynch et al. 1980, Talbot 1943). From March to November, when most ant species scramble around gathering food and fighting one another for space, winter ant seal themselves tightly in their nests. When November rolls around and other ant species tuck themselves in for their winter nap, winter ants unseal their nests and begin exploring the world. Because they are active when other ants sleep, they often miss the dangerous tides of invasive ants that can wipe out many other ant species (Holway 1998), and therefore persist in areas inhabited by other inhospitable ants. If they do happen to meet an adversary, they spray a toxic chemical from their rumps that scares off or even kills the would-be contender (Sorrells 2011).

How to spot them

At the beginning of winter, winter ants are hard to identify. Shiny reddish-brown with lighter yellow legs, they look like your everyday, run-of-the-mill ant. Early season, workers are about 0.1 inches long, just lengthy enough to span the letter “t” on this page. But as the season progresses and winter ants stock up on food, they become easier to identify.

To say a winter ant has a lot of “junk in her trunk” mid and late season is an understatement. When workers eat their favorite protein foods like insects and a sugary substance produced by other insects called honeydew, they stockpile the calories in special fat cells in their bums. These fat cells can grow to be tremendous; ant baby got back as it were. Because they waddle around with swollen rumps at the end of the season, some people call winter ants “false honeypot ants.”

To understand why they pack on the pounds, let’s poke our heads down into their rabbit hole. Winter ant colonies survive underground all summer on their rotund sisters’ fat. Their ample behinds are the world’s best refrigerators. Because fat cells are part of living tissue, as long as the worker is alive, the fat won’t rot like dead insects stored in the nest would. And because the fat is already concentrated and high in calories, workers don’t have to process it like they would other foods. Winter ants store enough fat in their portly posteriors to feed each other and all the babies that emerge as adults the following fall (Tschinkel 1986). When workers unseal their nests in the fall, they emerge as Skinny Minnies again.

Home deep home

Let’s travel a little deeper down the rabbit hole. While its worker inhabitants live a couple of years at most, winter ant nests can exist more than 10 years. The older the nest, the deeper it is (Tschinkel 1986). If we were winter ants crawling down into our home, we would enter through a short hallway leading to the first room. Other than the pinhole of light shining through the entrance, the whole house would be completely dark. To get from room to room, we’d have to smell our way with our antenna. Our rooms would have domed ceilings, tall enough for a couple of us to stand on top of each other. Because we’d have clingy feet, we could even walk on the ceiling!

We might have a few hundred sisters—sometimes up to 10,000 living with us—so every now and again, we’d bump into one of our sisters and give her a friendly tap with our antennae. If she seemed hungry, we might spit a bit of food for her to eat. If she seemed dirty, we’d help clean her with our mouths and antennae.

It might take us a long time to get all the way to the bottom. Remember, our nests are at least the human equivalent of a mile. Our older sisters live in the upstairs rooms, and our younger sisters live with our mothers deep down. Our queen mothers wander around the bottom of our nest in the dark laying their eggs. Our younger sisters help feed the babies and keep them clean while our older sisters gather food for us (Tschinkel 1986).

Life Underground

If were winter ants, we would not be able to hear well, and anyway it’s quiet so far underground. We can’t hear children running over us or leaves falling on our entrance. We don’t know somebody’s dad’s car just parked next to our own driveway. Beneath the roots, we don’t get wet when the sprinkler showers over our home and across the lawn in the summertime. We don’t hear the thud of the family dog flopping right on top of us to gnaw on a tennis ball. But it’s all there, all above us, all over the United States. If we were winter ants, we’d miss out on a lot about the fascinating lives of people. We’re lucky we’re not winter ants. We’re people, active all year long, and able to understand and delight in the winter ant’s secret wonderland, deep below our feet.

Find out more about this speciess at Antweb and see more photos at Alex Wild's photography site.