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How to identify it
- Larvae are grayish green with a wrinkled surface and rows of whitish dots, and reach 2/3 to 4/5 inch long when grown.[1]
- Larvae have seven pairs of fleshy prolegs, on abdominal segments two through eight, and a clasperlike rear end. Most caterpillar-like larvae feeding on foliage have five or fewer pairs.[1]
- Adults are stout wasps about 1/3 inch long with a broad waist, mostly black with some orange and yellow that varies between males and females and among species.[1]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| Pine sawflies (Neodiprion) | Also feed openly on conifer foliage, mostly on pines, but their larvae have relatively smooth skin rather than a wrinkled surface.[1] |
| Webspinning sawflies (Acantholyda) | Feed on conifers from inside silk nests rather than openly on the foliage.[1] |
| Caterpillars | True caterpillars, the larvae of moths and butterflies, usually have five or fewer pairs of prolegs on the abdomen; Susana larvae have seven.[1] |
Where it lives
In California the cypress sawfly occurs mainly along the coast and in southern California. At least six Susana species there feed on cypress, juniper or both.[1]
Biology and life cycle
Hosts are cypress and juniper; arborvitae and western red cedar are attacked less often. A chemical study of its larvae used Cupressus sempervirens as the host plant.[1][2]
Females insert eggs into the foliage, mostly in February and March in southern California and about a month later in the San Francisco Bay Area. There is one generation a year.[1]
Larvae feed from late winter to early summer, then drop to the ground and spin brownish, papery cocoons in the topsoil, where they spend the winter before pupating in late winter and spring.[1]
The larvae store terpenes from the host foliage in pouches off the gut and regurgitate them when attacked, which makes them well defended against predators such as ants.[2]
Damage and signs
- Larvae chew foliage, often in groups. Heavy feeding leaves a sparse canopy of clipped foliage and patches of bare stems.[1]
- Healthy trees and shrubs tolerate some foliage loss, but conifers that lose most of their foliage may die, especially small, young or already stressed plants.[1]
- Numbers are low in most years, and feeding is commonly harmless to moderate and does not threaten the long-term health of plants.[1]
Health risk
UC IPM describes it only as a plant pest and mentions no risk to people or pets.[1]
Control
Traps and physical control
If larvae are on only a small part of the plant, clip off the infested foliage or stems.[1]
Biological control
Fungal and viral diseases, birds, parasitic wasps, predatory beetles and small mammals kill many sawflies and help bring outbreaks down.[1]
Pesticides
Larvae are easy to kill with a thorough direct spray of almost any insecticide, including horticultural or narrow-range oil, insecticidal soap, neem oil or spinosad. Avoid broad-spectrum, persistent carbamates, organophosphates and pyrethroids, which harm bees and natural enemies. Bacillus thuringiensis (Bt) does not work because sawfly larvae are not true caterpillars.[1]
Common questions
- Are the green larvae on my cypress caterpillars?
- Probably not, if they are wrinkled, grayish green and have seven pairs of prolegs on the abdomen; those are Susana sawfly larvae, which are wasps rather than moths.[1]
- Will Bt control cypress sawfly?
- No. Bt does not work against sawfly larvae because they are not true caterpillars. Oils, insecticidal soap, neem oil or spinosad sprayed directly on the larvae do work.[1]
- Will cypress sawfly kill my tree?
- Usually not. Healthy hosts tolerate some foliage loss, but conifers that lose most of their foliage may die, especially small, young or unhealthy ones.[1]
Sources
- University of California Statewide IPM Program, “Cypress and Juniper Sawflies, UC IPM Home and Landscape.” ipm.ucanr.edu/home-and-landscape/cypress-and-juniper-sawflies/ (accessed 2026-11-09)
- Springer (The Science of Nature / Naturwissenschaften), “Cypress terpenes in sawfly larva of Susana cupressi (Hymenoptera: Symphyta: Tenthredinoidea) (Boeve et al. 2023).” doi.org/10.1007/s00114-023-01841-0 (accessed 2026-11-09)
- iNaturalist, “Susana cupressi taxon page (order and family).” www.inaturalist.org/taxa/890914 (accessed 2026-11-09)