Extension Logo
Extension Logo
University of Minnesota Extension
extension.umn.edu

Sawflies

Quick facts 

  • Sawflies are common in the landscape,  feeding on many trees and shrubs.
  • Sawfly larvae resembles butterfly and moth caterpillars so accurate identification is important.
  • Sawfly damage can affect the appearance of trees or shrubs but usually does not affect plant health.
  • There are several nonchemical and pesticide options for protecting trees and shrubs from sawflies

How to identify sawflies

A black fly with clear wings on a leaf
Adult female sawfly

Sawflies are related to wasps and bees.  Their name comes from the saw-like ovipositor (egg-laying structure) of adult females.  Adult sawflies are small, stout-bodied, non-stinging wasp-like insects, although they are seldom noticed in the landscape.

Differences between sawfly larvae and butterfly and moth caterpillars

Sawfly larvae are more commonly seen than adult sawflies. They look similar to butterfly and moth caterpillars. They differ from each other in the number of prolegs—the fleshy, leg-like projections on the abdomen.

Light green caterpillar with eight pairs of leg-like structures
Sawfly caterpillar
A green caterpillar with five pairs of leg-like structures
Caterpillars have fewer pairs of prolegs
  • Caterpillars have two to five pairs of prolegs on the abdomen.
  • Sawflies have six pairs of prolegs or more.
  • The prolegs on slug sawflies are small and may be overlooked.  
  • Sawfly larvae are smooth with little or no hair and are no more than one inch long when fully grown.  
  • Moth and butterfly caterpillars can be smooth, hairy or spiny, and vary in size when mature. They may often be larger than one inch long.

Biology of sawflies

Most sawflies in Minnesota have one generation per year (that is it takes one year to go completely through their life cycle once), although some go through two generations. 

Adult females use their saw-like ovipositors to cut slits into needles, leaves, or tender new shoots to lay eggs. 

Scars from egg laying by European sawflies
Egg laying scars from European sawflies
Yellowheaded spruce sawfly prepupa inside a cocoon.
Yellowheaded spruce sawfly prepupa inside a cocoon

Eggs hatch into larvae that feed on foliage of their host plants for about four to six weeks. 

  • It is common for most sawflies to feed gregariously, in non-social groups. 
  • When in such a group, if they are threatened, they can simultaneously raise and arch their bodies as a defensive tactic (presumably to scare away would be predators). 
Sawflies on alder showing defensive posture.
Sawflies on alder showing defensive posture

Many sawflies overwinter in the soil as pre-pupae (the stage between a mature larva and pupa) or pupae in cocoons; some species also overwinter as eggs or larvae.  Adults typically emerge in the spring or early summer.  

When sawflies are first active in the spring depends on:

  • Where in Minnesota they are found (generally the further north in the state, the later they will first become active).
  • Whether spring is early, late, or normal. 

Damage caused by sawflies

Sawfly feeding can vary from slight to severe.  The larvae typically feed in groups, and it is not uncommon for feeding to occur on just a few branches, although a severe infestation can cover an entire plant. 

Edge of leaf feeding by azalea sawflies.
Edge of leaf feeding by azalea sawflies

Conifer-feeding sawflies:

  • Some species emerge very early in the spring before new growth on trees has occurred and eat older needles from previous years.  
  • Sawflies emerging later in spring feed on new growth. 
  • A few species eat both new and old foliage, and these species can completely strip conifer trees of their needles in one season. 
Windowpane feeding by roseslugs.
Windowpane feeding by roseslugs

Deciduous plant-feeding sawflies

  • Larvae often feed along the edges of the leaves and can chew the leaf blade down to the midrib. 
  • Slug sawflies feed by chewing leaf tissue on one surface of the leaf between the veins, a type of feeding known as windowpane feeding. 
  • Damaged leaves at first are whitish; eventually these injured areas turn brown.  
Sawfly damage on confier with missing needles and partilly fed on needles.
Sawfly damage on conifer. Note the missing needles and partially fed on needles

Healthy, mature deciduous plants can typically tolerate sawfly feeding in one season.

  • Even when it is severe, as deciduous plants can regrow leaves. 
  • However, recently transplanted trees and shrubs and plants that have been severely defoliated in several consecutive years are more susceptible to injury. 

Sawflies attacking conifers feed on the surface of needles at first, leaving needles discolored, distorted, and straw-like. 

  • As the larvae grow larger, they consume entire needles. 
  • With the exception of tamarack, conifers do not regrow new needles once they are consumed. 

Even if sawfly defoliation does not impact plant health, defoliation may negatively affect the appearance of trees or shrubs.

How to protect your plants from sawflies

Management for sawflies depends on many factors:

  • Time of year 
  • Health of the plant
  • Conifer or deciduous tree or shrub
  • Number and size of sawfly larvae 
 | 

Sawflies on coniferous trees and shrubs

 | 

Sawflies on deciduous trees and shrubs

 | 

Slug sawflies on deciduous trees and shrubs

 | 

Sawflies on herbaceous plants

 | 

Authors: Jeffrey Hahn, Extension entomologist and John Lloyd

Reviewed in 2020

Share this page:
Page survey

© 2021 Regents of the University of Minnesota. All rights reserved. The University of Minnesota is an equal opportunity educator and employer.