Four species of woodpeckers (family Picidae) are definitely known to be predaceous on the western pine beetle in the Central Sierra Nevada Mountains in California. These are: Dendrocopus villosus, Dendrocopus pubescens, Dendrocopus albolarvatus and Dryocopus pileatus. The red-shafter flicker (Colaptes cafer, Picidae), creepers (Certhiidae), nuthatches (Sittidae), and flycatchers (Tyrannidae) are thought to be predators on the western pine beetle.
Predation by woodpeckers reduced the western pine beetle population by (a) actual consumption of 31.8% in two generations studied, and (b) by increasing parasite densities in the order of 3.85 factor. The increase in parasite density was believed to have been caused by bark removal to a near uniform thickness enabling a higher parasitism by those parasites with short ovipositors, such as Cecidostiba and Roptrocerus spp.
One adverse effect of woodpecker predation was a reduction or a depression of insect predation. Highly mobile insect predators may have been driven away by woodpecker activity, actually consumed, or both.
Bark flakes, chipped or pried off by the woodpeckers during their feeding activity, contained but few insects and it is doubtful that these could survive on the ground and reach the adult stage.