“Well, let me tell you, ants are the dominant insects. They make up as much as a quarter of the biomass of all insects in the world… And the rest of life is substantially dependent upon them.”
~E.O. Wilson
Here’s another one of the stories from my book series, Walks with a Naturalist. This one, Hot Ants, is from Volume 1. Stay tuned at the end for some fun follow-up from recent explorations in the park, and how bears relate to this whole thing!
Hot Ants
When Mike and I visit Yellowstone, we always carry an infrared thermometer. It’s like the ones that doctors sometimes use. You point it at something and pull the trigger, and it measures the temperature. In Yellowstone, an infrared thermometer is perfect for taking the temperature of hot springs because you aren’t allowed to touch them. They could burn you, and some contain chemicals that aren’t good for you!
One time, we were hiking in Yellowstone with our infrared thermometer, and Mike noticed a huge ant mound. It was about the size of a squishmallow. The top of the mound was covered with short needles from fir trees. The needles were old and brownish-orange, not fresh and green like the ones on the trees.
There were ants crawling on the mound and on the ground nearby. The ants had red heads and black abdomens. They were bigger than the sugar ants that come into our kitchen. They were smaller than the huge carpenter ants we see in rotting logs.
Mike pointed the infrared thermometer at the ground. It was 85 degrees. Then he pointed it at the ant mound. It was 95 degrees! The ants had built their mound in a sunny spot. The heat from the sun warmed their mound. Later that night, the fir needles on the top of the mound would keep it warm, like the blankets on your bed keep you warm at night. Ants need to be warm to grow and survive.
Mike and I enjoyed watching the ants. Some ants took care of the mound. They made sure the needle blanket covered the whole mound. Other ants went out to collect honeydew from aphids. Aphids are insects that feed on the sap of plants. Their waste is honeydew, a sweet liquid that the ants like to eat. We also noticed that some ants would find dead insects and carry them back to the nest for food.

After doing some research, we discovered these ants are called western thatch ants. The word “thatch” means a roof made from plants. That’s just what the ants did – they built a mound with a roof made from plants!
See if you can find ant colonies near your home. What are your ants doing? What type of home do they live in?
Last week, I had the privilege to lead the NC Museum of Natural Sciences’ Yellowstone Institute with twelve amazing teachers from all over North Carolina, plus two awesome coworkers from the Museum. On our last morning, we took a final visit to Lamar Valley to look for wildlife. One of the first wildlife encounters of the day was a male black bear on the side of the road. We watched from the safety of the vehicles as it stopped and dug in a bunch of spots.

After the bear crossed the road and moved away from where we were parked, we hopped out of the vans to figure out what it was after. We found a number of spots where we could tell it had been digging by the streaks of fresh soil on top of the vegetation and usually at least a small hole, too.

Each place the bear had dug, ants were scurrying everywhere. Many of them were carrying larvae or pupae, much like you’ve probably seen them do if you’ve ever turned over a rock or a log and disturbed an ant nest. We could only assume the bear was digging up ant nests and eating the ants!

You might also notice the pieces of dead vegetation surrounding this hole. The bear was targeting the mounds of thatch ants, like the ones in my story, for its breakfast!
About a week later, Mike and I were out in the park and spotted a cinnamon-colored black bear in the same area where the workshop group at seen the black bear digging. This bear seemed more intent on turning over rocks than throwing dirt around.


Once again, after the bear moved on, we got out to take a look at what it was up to. We found a number of flipped rocks, and again, most were swarming with thatch ants!

Though I knew bears ate ants, it was really neat to see that behavior in action! A little googling brought up a number of scientific studies on ant-foraging by bears. I found this gem of a quote in a study in a 2004 issue of Western North American Naturalist: “A 41-kg, 2.5-year-old male bear shot in mid-July as a nuisance bear had consumed 2.1 kg (wet weight) of Formica, approximately 7840 workers and 54,700 brood [larvae and pupae]. The value of this meal was about 695 calories, which would have provided about 37% of this bear’s daily maintenance requirement.” That’s a lot of ants! The authors of the paper suspect that bears are preferentially searching for and consuming ant larvae and pupae because they are more digestible than adults and have no way to defend themselves.
Taking that a step further, a 2014 study suggested that bear predation on ant nests caused a trophic cascade. You’ve probably heard about the tropic cascade tied to gray wolves: more wolves means less elk which means healthier aspens and willows (among other things). Recent publications are showing it’s nowhere near as simple as that… but wolves most certainly play a role.
In the bear-ant case, here’s how it plays out. Thatch ants protect sap-sucking insects and collect their honeydew, as I described in my story. Without bear predation, the sap-sucking insects (in the case of the 2014 study, leafhopper nymphs) thrive under the protection of the ants. More sap-sucking insects means more damage to their host plants. But in areas with increased bear predation on ants, there weren’t as many ants remaining to guard the leafhopper nymphs, allowing predators of the nymphs to swoop in and eat them up, leading to few leafhopper nymphs. With fewer leafhopper nymphs, there was less stress on the plants, and the plants grew measurably better. It’s always amazing to rediscover just how interconnected the natural world is!



































