**Oakworm Sawflies** (*Caliroa* species, or other sawflies that mimic oakworms) are the larvae of non-stinging wasps that feed on oak foliage. The conflict is visible **defoliation**, often causing the leaf to appear “skeletonized” (only the veins remain). While the damage is aesthetically displeasing, sawfly defoliation is typically **less severe** than true oakworm moth outbreaks, and healthy trees can generally recover. However, high populations can stress young or recently planted trees.
Taxonomy and Classification
Sawflies belong to the order Hymenoptera (Wasps, Ants, and Bees). They undergo complete metamorphosis. Sawfly larvae are often confused with caterpillars, but they possess six or more pairs of prolegs on the abdomen (caterpillars have five or fewer). The adult is a fly-like wasp that lacks the constricted “waist” of true wasps and uses a saw-like ovipositor (egg-layer) to insert eggs into plant tissue.
Physical Description
The destructive larvae are 1/2 to 3/4 inch long.
- **Larva (Key ID):** Slug-like, often dark, shiny, or slimy-looking due to a mucous covering (e.g., Oak Slug Sawfly). They have more prolegs than true caterpillars.
- **Damage Sign (Key ID):**
- **Skeletonization:** The larvae feed on the soft leaf tissue between the veins, leaving behind a brown, net-like skeletal structure.
- **Feeding Preference:** Damage is often concentrated on the underside of leaves.
- **Conflict:** Aesthetic leaf damage and minor tree stress.
Distribution and Habitat
Oakworm Sawflies are found throughout areas where oak trees grow. Their habitat is the foliage of oak, especially the leaves of the lower canopy and younger branches.
Behavior and Conflict
The conflict is primarily limited to leaf appearance.
- **Nocturnal Feeding:** Some species feed primarily at night and rest on the undersides of leaves during the day.
- **Chemical Sensitivity:** Unlike many caterpillars, sawfly larvae are generally highly susceptible to common insecticides, making control simpler if needed.
- **Multiple Generations:** Many species have multiple generations per season, requiring sustained monitoring.
Management and Prevention
Control is integrated pest management (IPM), favoring manual and low-impact treatments.
- On small trees, a strong jet of water can be used to dislodge the slug-like larvae, which often die before finding their way back to the foliage.
- **Horticultural Soap/Oil:** Apply insecticidal soap or a light horticultural oil spray, ensuring complete coverage of the leaf undersides, to kill the larvae by contact/smothering.
- **Targeted Insecticide:** Traditional caterpillar-specific controls like *Bacillus thuringiensis* (Bt) are **ineffective** against sawfly larvae (Bt only affects Lepidoptera). Use a general-purpose insecticide for soft-bodied pests if populations are high.
Conservation and Research
Oakworm Sawflies are managed as landscape pests. Research focuses on understanding their resistance to common chemical controls and enhancing the role of their specialized parasitic wasp and fly enemies.