[University Research] Arthropods: Saving the Planet?

Just when you think you can’t look at one more cockroach, ant, millipede or spider, they go and do something sweet. We’re talking, of course, about how these arthropods and their brethren share their voracious appetites with our trash-laden cities. They are cleaning up the streets of New York and other cities across the United States.

North Carolina State University researcher and entomologist Dr. Elsa Youngsteadt offers proof. Youngsteadt and her colleagues recently released data from a study they conducted in Manhattan, which reveals the powerful role arthropods play in our urban ecosystems. Study results indicate that these literal litterbugs dispose of tons of trash that would otherwise be cluttering our streets, attracting rats, threatening public health, compromising the environment and presenting our city governments with an undue financial burden.

“We calculate that the arthropods on medians down the Broadway/West Street corridor alone could consume more than 2,100 pounds of discarded junk food, the equivalent of 60,000 hot dogs, every year — assuming they take a break in the winter,” says Youngsteadt. “This highlights a very real service that these arthropods provide. They effectively dispose of our trash for us.”

This is good news because this trash removal not only reduces toxin levels and increases our cities’ aesthetical appeal but also helps keep urban rat populations in check. Youngsteadt explains, “Ants and rats are competing to eat human garbage, and whatever the ants eat isn’t available for the rats.” Particularly in New York, where it’s often said that rats outnumber, (or at a minimum) equal, residents, competition is a very good thing.
 

Setting the Stage.

In conducting the study, Youngsteadt and her research team placed junk food that would characteristically be found in our city streets — cookies, potato chips and hot dogs — in 21 city parks and 24 street medians. Two carefully measured food samples were set out at each site: one enclosed by a cage (restricting entry to insects and other small arthropods); the other placed out in the open so that rats, pigeons and other vertebrates could join in the delicious feast.

The purpose of the median-vs.-park placement was to determine whether biological diversity made a difference in consumption levels. (Arthropod diversity was greater in the parks, with an average of 11 hexapod families and 4.7 ant species per site, as compared to an average of nine hexapod families and 2.7 ant species per median site.) The researchers expected consumption to increase with diversity.
 

Analyzing the Results.

How much did the unwitting study participants actually eat? Much more than the researchers had expected. They collected and measured the remaining food after 24 hours and found that arthropods ate what would amount to 4 to 6.5 kilograms (about 9 to 14 pounds) of food waste a year in a single street median (which extrapolates out to the ton quoted previously for the Broadway/West Street corridor).

Surprisingly to the research team, consumption was notably higher — two to three times higher, in fact — in the medians. They attributed this difference to the presence of the pavement ant (Tetramorium species), a particularly efficient urban forager, in the median areas. Not surprisingly, the uncaged food samples had definitely been shared with other diners — vertebrates who clearly compete with arthropods for food. So, as Youngsteadt concludes, “Both groups of animals (bugs and vertebrates) want the stuff we drop. We have met our urban biodegraders: Their work behind the scenes is making our garbage disappear.”

So go ahead and curse them when they’re causing your customers distress in and around their homes. But when you see a swarm of ants piled up on a city sidewalk, tip your hat with a word of thanks: These hard-working environmental stewards deserve our respect.

Donna Defranco is a freelance writer based in Cleveland, Ohio, and a frequent editorial contributor to PCT magazine.

Editor’s note: The original research cited here appeared in “Habitat and species identity, not diversity, predict the extent of refuse consumption by urban arthropods,” by Dr. Elsa Youngstead, Ryanna Henderson, Dr. Amy Savage, Andrew Ernst, Dr. Rob Dunnand, Dr. Steven Frank, North Carolina State University; published Dec. 2, 2014, in Global Change Biology.