Caterpillars & Leaf-Chewers
A range of larvae and beetles chew bonsai foliage: butterfly/moth caterpillars, sawfly larvae (which can strip pines and other conifers), leaf beetles…
Caterpillars & Leaf-Chewers at a glance
| Also known as | Caterpillars, sawfly larvae, leaf-eating beetles |
|---|---|
| Affected parts | Leaves, shoots |
| Most at risk | Broadleaf and some conifers in spring/summer (elms, oaks, larch, pines, crabapple) |
| Main cause | Larvae/beetles eating foliage |
| Severity | Cosmetic to severe — a colony can defoliate a small tree fast |
| Reversible? | Yes — remove pests; the tree re-leaves |
What to look for
- Leaves: Irregular holes, chewed edges, skeletonised patches, or whole leaves/needles eaten; leaves rolled or webbed together (leaf-rollers); small dark droppings (frass) on leaves and soil.
- Whole tree: The culprits themselves — caterpillars or sawfly larvae lined up along shoots/needles, often on the undersides or hidden in rolled leaves; rapid loss of foliage.
Overview
A range of larvae and beetles chew bonsai foliage: butterfly/moth caterpillars, sawfly larvae (which can strip pines and other conifers), leaf beetles, and leaf-rollers/tiers that fold leaves into shelters. Because a bonsai has so few leaves, a single hungry colony can do disproportionate, even total, defoliation in days.
Causes
Egg-laying by moths/butterflies/sawflies in spring–summer; nearby host plants; mild seasons that boost numbers.
Commonly confused with
Vine-weevil adults notch leaf edges (not holes through the middle) and the real damage is at the roots. Slugs/snails leave slime trails. Hail damage tears leaves without frass. The presence of frass and visible larvae confirms chewers.
Which species are affected
Most broadleaf species (elms, oaks, hornbeam, beech, crabapple, fruiting trees) and some conifers (pine and larch sawflies); seasonal, mainly spring and summer.
Treatment
Hand-pick caterpillars/larvae (effective on a small tree); for caterpillars, Bacillus thuringiensis (Bt) is a selective biological spray; insecticidal soap or a contact/systemic insecticide for heavy or sawfly attacks. Remove rolled/webbed leaves with the larvae inside. Inspect daily during an outbreak.
Prevention
Inspect regularly in the growing season (check undersides and shoot tips); remove eggs/larvae early; encourage birds and predatory insects outdoors; net valuable trees during heavy moth flights.