Boars Caught Washing Their Food

It may be time to rethink the insult “eat like a pig.” Researchers have found that boars aren’t total slobs at dinner and will take the time to wash their food before chowing down.

This is the first time that food washing has been documented in pigs, and its discovery was a happy accident. Shortly after three new wild boars arrived at Switzerland’s Basel Zoo in 2013, local press came to see the new residents and their exhibit, which had a sandy ground and a creek running through the middle. During the press visit, keepers tossed apple pieces to the pigs so they’d be active for the guests. Amid the excitement, the zookeepers noticed something odd: When the pieces of apple got sand stuck to them, the boars carried them over to the creek and pushed them around in the water with their snouts before eating.

After hearing about this, anthropologists Volker Sommer and Adrianna Lowe arrived at the zoo to follow up on the keepers’ observations with an experiment. For several days, they denied the boars their morning meal and then gave them some sandy apples and some clean apples in the afternoon.

All of the adult boars carried at least some of the dirty apples to the creek, the researchers say, "where they set them down in shallow flowing water or puddles and pushed them to and fro with their snouts.” After a quick rinse, the apples were sand-free and the boars began eating. In some cases, they ate a few apple pieces right away before washing other ones. The clean apples were never washed before being eaten.

That the boars selectively rinsed the sandy apples and not clean ones suggests that they’re really washing them, the researchers say in their report of the study, and not merely moistening them to make them easier to swallow or change their texture. As for why the pigs immediately ate some dirty apples without washing them, the researchers think that the boars might have had trouble seeing the sand and sometimes needed to taste it before deciding to wash the apples. Since they skipped breakfast, they might have also been too hungry to bother with washing first. 

During the experiment, one of the boars seems to have come up with an alternate apple-washing technique. After a few days, he stopped carrying the food to the creek and instead bit the dirty apples into pieces and dropped them on the ground. Then, the scientists say, he “produced considerable amounts of saliva, which he dropped repeatedly and in a targeted fashion over the apple halves, before eating the so-cleaned fruit pieces.”

Next, the researchers want to try to figure out if other boars wash their food or if the behavior is unique to this group at the zoo. They also want to know whether the behavior is innate, figured out through trial and error by each animal or learned from other boars. Keepers at the other zoos where the boars had come from said they’d never seen the animals washing their food, and they only started doing it at Basel Zoo. One of the pigs, though, was known for eating while standing in the water at his previous home. He may have learned the benefits of rinsing his food there and was imitated by his new roommates when he arrived at Basel.