Hungry caterpillars unlikely source of carbon emissions, researchers say

By Joe Morgan via SWNS

Hungry caterpillars are an unlikely source of carbon emissions, warns a new study.

While they're unlikely to gorge on swiss cheese and chocolate cake like in the children's classic, caterpillars' hunger for leaves can cause large quantities of greenhouse gases.

Outbreaks of caterpillars of invasive gypsy moths and forest tent caterpillar moths occur at least every five years in temperate forests resulting in so many leaves being eaten that the results drastically impact the environment.

On the positive side, the nutrient-rich insect poo, officially called 'frass', can wash into lake water and act as a fertilizer for microbes which boosts the health of the water.

But also, researchers warn the increasing quantities of frass will favor the growth of greenhouse gas-producing bacteria in lakes at the expense of algae that removes carbon dioxide from the atmosphere.

Experts say as the climate becomes generally warmer, caterpillar outbreaks in temperate climes could become more frequent and more of a danger to carbon-reducing plants.

The study of 12 areas in Ontario, Canada, found in years with insect outbreaks, the leaf area of forests was reduced by 22 percent.

At the same time, nearby lakes contained 112 percent more dissolved nitrogen and 27 percent less dissolved carbon compared to non-outbreak years.

The effects were greatest when lake catchments contained higher proportions of deciduous broadleaved trees, such as oaks and maples, which the caterpillars favour over coniferous trees like pines.

In years without outbreaks of leaf-eating insects, carbon and nitrogen entering lakes usually comes from decaying leaf and needle litter, and peaks in quantity in autumn.

Professor Andrew Tanentzap in the University of Cambridge, said: “These insects are basically little machines that convert carbon-rich leaves into nitrogen-rich poo.

"The poo drops into lakes instead of the leaves, and this significantly changes the water chemistry - we think it will increase the extent to which lakes are sources of greenhouse gases."

Dr. Sam Woodman, also at the University of Cambridge, said: “Outbreaks of leaf-eating insects can reduce the carbon dissolved in lake water by almost a third when the trees around the lake are mainly deciduous.

"It’s just amazing that these insects can have such a pronounced effect on water quality."

He added: “From a water quality perspective they’re a good thing, but from a climate perspective they’re pretty bad – yet they’ve been completely overlooked in climate models.”

The study was published in the journal Nature Communications.