comparison of sawfly larva and caterpillar
Source: Michigan State University.  IPM Scouting in woody landscape plants.  MSU publication E-2839.

Description of Sawflies

Sawflies are wasps.  They don’t look like wasps (in the minds of most people).  They look like fat-bodied flies without the pinched waist that is characteristic of the better-known wasps.  Sawflies have four wings, while all of the true flies have only two.  Sawfly wasps cannot sting.   

Sawfly larvae look like hairless caterpillars.  They feed on the foliage of plants unlike better-known wasps such as hornets, yellowjackets and paper wasps whose larvae feed on insects.  Sawfly larvae look like caterpillars but have small differences that are sometimes hard to determine.  Sawfly larvae have prolegs (stubby, unsegmented, fleshy pairs of legs) on every segment of the abdomen whereas caterpillars have prolegs in the middle and at the tail end.  Caterpillars may have up to five pairs of abdominal prolegs but never more. Sawfly larvae always have six or more pairs.  

Life Cycle of Sawflies

Sawflies got their name from their ovipositor – the egg-laying apparatus at the end of the female’s abdomen.  When the female is ready to lay eggs she uses the ovipositor to saw a slit in a leaf, needle or stem.  Eggs are then deposited into the slit.

All ants, bees, wasps and sawflies have a complete life cycle of four stages, egg, larva, pupa and adult.  The larva is a worm-like immature that eats and grows until it forms a pupa and transforms to the adult stage (the way a caterpillar changes into a butterfly).

Damage of Sawflies

Sawfly wasp larvae are plant eaters.  Most resemble caterpillars in general appearance and also in damage.  Many sawflies are plant pests that cause noticeable-to-destructive loss of plant foliage.   Sawflies often feed in groups and can quickly defoliate portions of their host plant.  Sawflies are host-plant specific; that is each different species of sawfly feeds on a specific host plant and does not move from one plant type to another.  For example, the European pine sawfly larvae are gray-green larvae with shiny black heads that live in clusters and eat pine tree needles in May; they will not feed on other plants.  Similarly the dogwood sawfly larvae that eat entire leaves from gray and red osier dogwood plants in late summer will be found only on dogwood shrubs.

Some of the more common sawflies that feed on trees and shrubs in Iowa are listed below.

Sawfly  (with link)

Host Plant(s) 
Ash Sawflies Ash
Pear Sawfly or Pearslug Pear, cherry, crabapple, apple, plum, hawthorn, cotoneaster, and mountain ash
Oak Sawflies Oaks (varies with sawfly species)
European Pine Sawfly Mugho, scots and red pine
Dogwood Sawfly Dogwoods
Rose Sawfly or Roseslug Roses

Management of Sawflies

Defoliation, which may range from spotty to complete, is not usually fatal to healthy, well-established trees and shrubs.  Small, newly transplanted and stressed trees may warrant protection from severe defoliation.  Otherwise, control is probably not justified.  It is typical to discover the damage after the larvae have finished feeding and dropped from the leaves.  In this case, it is too late to take any effective action.

Management of sawflies should be done while the larvae are still small.  Sawfly larvae can be physically removed from infested trees if there are only a few on small plants.  If handpicking is not practical, chemical control may be warranted, but only when large numbers of larvae and a serious damage potential exist.  Sprays applied after larvae have left the leaves do no good.

Most garden insecticides can be used to control sawfly larvae when control is warranted.  Be sure the specific host is listed on the insecticide label before you use the product.  Read and follow label directions.

Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Yard and Garden, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on September 13, 2016. The information contained within may not be the most current and accurate depending on when it is accessed.