Even though they're mostly ignored and often maligned, city insects are some hard-working New Yorkers. By consuming littered food waste, they dispose thousands of kilograms of garbage from the streets of Manhattan every year. And they compete with rats for access to our littered food. The findings were published in Global Change Biology this week.
Parks and other urban green spaces provide a welcome oasis in a city that never sleeps. And a closer look reveals how the tiny residents of even the smallest green spaces (like street medians) provide ecosystem services that help improve the public health and aesthetics of the whole city.
To study this novel ecosystem service provided by litter-eating arthropods, a North Carolina State University team led by Elsa Youngsteadt placed carefully measured quantities of junk food like cookies, potato chips, and hot dogs on street medians (24 sites) and city parks (21 sites) throughout the city. And then 24 hours later, they measured the food consumption and removal. The team also studied arthropod diversity—from insects to spiders to millipedes—as well as various environmental conditions that affect them, like temperature and humidity. They ended up extracting 16,296 bugs (including 32 species of ants) using an aspirator, The New York Times reports.
They found that arthropods are capable of removing between 4 and 6.5 kilograms of food in a single street median per year (or least during their several active months). “This isn't just a silly fact," Youngsteadt explains in a news release. "This highlights a very real service that these arthropods provide. They effectively dispose of our trash for us." Assuming the insects take a break in the wintertime, their calculations show that arthropods on medians down the Broadway and West Street corridor alone consume more than 950 kilograms of discarded junk food every year—that’s the equivalent of 60,000 hot dogs.
Arthropod diversity was greater in parks than in medians, with an average of 11 hexapod (six-legged) families and 4.7 ant species per site compared to 9 hexapod families and 2.7 ant species per site. Yet surprisingly, arthropods in medians removed two to three times more food per day than those living in parks. "We think this is because one of the most common species in the medians was the pavement ant (Tetramorium sp. E), which is a particularly efficient forager in urban environments," Youngsteadt says. Species identity and habitat, they find, may be more relevant than diversity for predicting these ecosystem services. Greater food removal was also linked to hotter, drier conditions, which likely increased arthropod metabolism.
Furthermore, more food was removed when (less desirable) vertebrates like rats and pigeons also have access to food. The team had placed two sets of food at each site: One in a cage so only arthropods can reach it, another out in the open for other animals to eat it too. "This means that ants and rats are competing to eat human garbage, and whatever the ants eat isn't available for the rats," Youngsteadt explains. "The ants aren't just helping to clean up our cities, but to limit populations of rats and other pests."
“You may not like ants,” she tells the Times, “but you probably like rats even less.”