- Leaf skeleton: slugs, beetles, sawfly larvae, Xanthogaleruca beetles
- Leaves rolled into tubes or tied together with silk threads: leaf rollers (moth silkworms)
- Grooves between the upper and lower surfaces of leaves. Insects or tears may be visible when the leaves are held to the light: leaf miners
- Leaves fall in early summer. Cutting along the petiole will reveal insect larvae: leaf borers, caterpillars or sawflies, maple leaf borers
- Twig borers and elephant beetles.
- General deterioration of the entire tree or a particular branch. Holes in the bark, accumulation of lint, sawdust or insects: stem borers, beetles, webworms
- General deterioration of plants, gnawed root areas: larval stages of weevils, beetles and caterpillars.