Wildlife ecologist Sophie Petit was camping on South Australia’s Kangaroo Island one night in 2016, when she noticed something unusual: sugar ants swarming a spot in the sand where she had urinated a couple of hours earlier. To her wonder, the ants came back, night after night, seeking more pee.
Now, 3 years later, Petit has found that the insects crave the urine of people, kangaroos, and other animals, likely to survive the island’s nutrient-scarce environment. They even prefer it to sugar water.
One year after her camping trip, Petit, who is based at the University of South Australia, Mawson Lakes, returned to Kangaroo Island with another colleague. The Rhode Island–size locale is full of dry scrub and woodlands, and its fire-prone bush grows on sandy, nutrient-poor soil. It’s also home to tens of thousands of kangaroos—hence its name.
The researchers wondered what exactly the ants were getting from the pee. Outside of water, the main chemical component of urine is urea, a compound containing nitrogen, which all living creatures use to build proteins and other biological molecules. The researchers prepared several solutions: some containing the urea concentration found in human and kangaroo pee (2.5%), some containing up to 10% urea, and some that were just sugar water. Then, they poured them on the sandy ground at night and waited for the sugar ants (Camponotus terebrans) to come.
After 1 month of observations, the team discovered that the higher the concentration of urea, the more sugar ants. And despite their name, the insects favored even the relatively low urea content kangaroo and human urine over the sugar water, the scientists report this month in Austral Ecology.
What’s more, the ants scoured the stains night after night for weeks, long after the sand had dried. They even tunneled inches down into the sand in their quest for urine residue. Petit watched in awe as the ants doggedly excavated the urine stains, expecting them to eventually move on. But, every time she checked, she says, “They were still at it.”
Other ants are known to harvest nitrogen from urine, but this is the first time the insects have been observed mining dry urine from the sand.
Petit believes the ants are after the urea, from which they can extract nitrogen. The soils on the island are “notoriously poor in nitrogen,” she explains.
“Urine is effectively nature’s sports drink,” says Michael Kaspari, an ecologist at the University of Oklahoma, who was not involved with the study. He says urine patches may be particularly valuable for ants, which often have stationary colonies and thus can exploit the same nearby patch over and over. “For a lucky colony,” Kaspari says, “a good urine dump is a resource that keeps on giving.”
*Correction, 27 December, 2 p.m.: This story has been updated to correct Michael Kaspari's name.