Ants, Oleic Acid, and Breakfast Cereal
I found this posted on a subreddit called /whatsthisbug and I got so curious about one of the answers.
Image says “My son put some Trix in his ant farm. Instead of eating them, the ants dug up all of the dead ants in the farm and piled them on top of the Trix. Not sure what that means but I’m not eating Trix anymore.”
Reddit user /u/Desirai wrote in reply:
Oleic acid, I presume. It's used in a lot of artificial food and is responsible for the smell of dead ants. The ants are probably just responding to the new mega graveyard they just found.
With an answer like this I had to do some research. Turns out that E. O. Wilson, the entomologist, was studying Ants in the 1950’s at Harvard when he observed that when an Ant died they remained right where they had died, for about two days. Then after two day time period any Ant walking by said dead Ant would come and collect the dead-Ant, and bring them to a refuse pile of also dead-Ants and through the new dead-Ant on the pile. He got to figuring out what was triggering this recognition of death for the Ants and began testing different chemicals by putting a dropper full whichever solution he was experimenting with on an Ant and just watched what happened. He tried a few different compounds, including skatole, a chemical found in feces, and trimethylamine, what we might recognize from the scent rotting fish. One day he tried placing a drop of oleic acid on a random Ant in an observed colony in his lab and watched as another Ant came by and picked the oleic acid drenched Ant up and dragged her off to the pile of dead Ants. It took many repeated efforts by the oleic acid Ant to clean herself off, and many attempts before she finally entered back into the colony without being picked up and carried off again back to the dead Ant graveyard. E. O. Wilson concluded that oleic acid is released when Ants die as a chemical cue to the rest of the colony to clean up the dead and get rid of them before whatever may have killed them infects the rest of the colony, or, you know, just to clean up the decaying body and move it aside where it won’t get in the way. This behaviour of clearing out the dead is called “necrophoretic behaviour”. I read that oleic acid stimulates necrophoretic behavior in multiple Ant species and also with Termites. For Isopods (Pillbugs for example), Caterpillars, Crickets, Cockroaches, and Bumble Bees it induces avoidance behavior. I think this makes sense. If I smelled a dead human kicking around my house, I would either avoid them or try to get them out of the house.
But my curiosity keeps on with wondering how is this related to food? I have read that oleic acid is found in meat (beef, chicken, pork), cheese, eggs, olives, avocados, nut oils, among other foods folks routinely consume. It is one of the most common fatty acids on earth. It’s even found within our cells. Turns out oleic acid is also an additive in processed foods to help prevent the food from spoiling due to fungi. The oleic acid is known as a fungistatic, meaning it inhibits the growth of fungi. It is often added to bakery goods to help them stay fresher longer. Trix cereal contains “Canola and/or Sunflower oil” and this could be where the oleic acid gets into the mix.
Ingredients
Whole Grain Corn, Sugar, Rice Flour, Corn Syrup, Canola and/or Sunflower Oil, Salt, Trisodium Phosphate, Natural and Artificial Flavor, Red 40, Yellow 6, Blue 1 and Other Color Added, Citric Acid, Malic Acid, Vitamins and Minerals: Calcium Carbonate, Tricalcium Phosphate, Vitamin C (Sodium Ascorbate), Iron and Zinc (Mineral Nutrients), a B Vitamin (Niacinamide), Vitamin B6, (Pyridoxine Hydrochloride), Vitamin B2 (Riboflavin), Vitamin B1 (Thiamin Mononitrate), Vitamin A (Palmitate), a B Vitamin (Folic Acid), Vitamin B12, Vitamin D3.
Does the oleic acid in these foods act as a formic deterrent? Or would it act as an attractant? Would an Ant try and drag her dead friend over to my peanut butter? If not, why not? Is it a certain concentration or combination of various chemicals? More questions all the time.
As for the original Twitter post, I don’t think I’ll be eating Trix anytime soon either. Not because the oleic acid, or the Ants dragging their dead to the Trix pieces, but instead because I had never eaten them before and can’t start; they just don’t sell Trix in Canada.
To learn more :
A death pheromone, oleic acid, triggers hygienic behavior in honey bees (Apis mellifera L.)
The fungistatic action of oleic acid