New York, Dec 4 (IANS): Insects play a very important role in cleaning up cities and they compete with other pests like rats and pigeons in their endeavour, a study has said.

Scientists sampled arthropods - such as insects and millipedes - in street medians and parks in Manhattan, US to measure rates of garbage consumption.

They placed two sets of junk food outside, one covered with nets so that only insects could access it and another that was accessible to all scavengers.

The researchers found that insects ate huge amounts of the junk food, and cleared up the garbage.

"The ants aren't just helping to clean up our cities, but to limit populations of rats and other pests," said Elsa Youngsteadt from North Carolina State University.

They were also surprised to learn that arthropod populations in medians ate two to three times more junk food than those in parks - even with less biodiversity than the medians.

"We think this is because one of the most common species in the medians was the pavement ant, which is a particularly efficient forager in urban environments," said Youngsteadt.

The team calculated that the arthropods on one street alone, the Broadway/West St. corridor, could consume more than 950 kg of discarded junk food.

"This highlights a very real service that these arthropods provide. They effectively dispose of our trash," Youngstead explained.

Even flooding with salty water from Hurricane Sandy, that hit New York had no measurable impact on the food consumption by arthropod population.