Bark Lice vs. Borers on Red Oak: Expert Debate in Illinois

An Illinois certified arborist reports orange powder and webbing on red oaks in Warrenville (Chicago suburbs). Initial expert opinion suggested borer frass; the arborist disagrees, citing no exit holes, tree health, and distribution on branches. Identifies it as bark lice (psocids), common in the South.

Resolution: Bark Lice Confirmed

The arborist is correct. Key distinguishing features:

• Bark lice (Psocids): Fine silvery webbing on trunks/branches; orange powder is metabolic waste, not frass. Insects are tiny (1/4"), brownish-black, winged adults; wingless nymphs. Feed on lichens, fungi, dead organic matter—not living tree tissue. Harmless.
• Borers: Coarse frass at entry holes; exit holes; canopy dieback; bark cracking.

Chicago-Area Context

While bark lice are more southern, they occur in Illinois. However, the Chicago region faces serious invasive threats: emerald ash borer, Asian longhorned beetle, gypsy moth. The arborist's recommendation to contact:

• Illinois DNR Forestry: dnr.state.il.us
• Chicago City Forestry: Joseph McCarthy (312-747-2098) or Karen Nowacki (312-744-7080)

is prudent for ruling out regulated pests.

Management

No control needed for bark lice. If webbing is objectionable, a strong water jet dislodges them. They perform beneficial scavenging. Populations peak in fall, decline in winter.