The Colorado State Forest Service says the pine sawfly, a native insect that defoliates ponderosa pines, has reached "epidemic" levels south of Denver.
The outbreak was detected a few weeks ago and is believed to have started near the border of El Paso and Elbert counties. Foresters say the infestation has now been found on the northeastern fringes of the Douglas County border.
Residents in the area can expect to see severe defoliation of pines that are affected and large numbers of sawfly larvae in and below the trees.
Meg Halford with the forest service's Franktown district says the latest outbreak is exceptional because of the large number of eggs deposited on pine needles by adult sawflies last fall. It's unclear what environmental factors might have accelerated the spike in the sawfly population.