Sawflies

While it might be cute to picture a fly buzzing around with a tiny saw, there is nothing to love about sawflies.

Sawfly larvae (Charles J Sharp) CC BY-SA 4.0

Sawflies get their name because their ovipositor (egg-laying organ) is shaped like a saw and used to cut notches into plants for egg-laying.

Sawfly description

Sawfly larvae may look like caterpillars or slugs, but these pests are in the same order as bees, wasps, and ants, and are closely related to woodwasps and horntails. You can tell the difference between sawfly larvae and caterpillars by counting their legs. Caterpillars usually have five or fewer prolegs on their abdomen, while sawfly larvae, such as the California pear sawfly, have 7 or 8 pairs of prolegs on their abdomen and 3 more pair on the thorax.

​With over 8,000 sawfly species, spread out over 800 genera, there is a wide variety of coloration and body type in the world of sawflies. As a group, their soft bodies are stubby and only slightly wasp-like, and they tend to be weak flyers. The ovipositor is often mistaken for a stinger, though sawflies cannot sting. Some sawfly larvae, however, are known to puke up a noxious liquid that would-be predators find distasteful, while other sawfly species raise their rear ends up, cobra-fashion, weaving back and forth a warning.

Sawfly species

Some of the more common sawfly species include:

• California pear sawfly (Pristiphora abbreviata) - defoliates older pear trees
• currant sawflies (Nematus ribesii) - defoliates currant, gooseberry, and other Ribes
• dock sawfly (Ametastegia glabrata), or dock falseworm - burrows into orchard fruit and feeds on members of the buckwheat family, including bindweed, knotweed, and sorrel 
• green or tan spotted imported currantworm (Nematis ribesii) - strips foliage off currants and gooseberries
• pear or cherry slug (Caliroa cerasi) - a serious skeletonizer 
• light or dark striped raspberry sawfly (Monophadnoides geniculatus) - feeds on blackberry, loganberry, raspberry, and strawberry leaves
• false webworms (Acantholyda erythrocephala) - colonies spin silken nests in pine trees that become filled with discarded food, cast skins, and fecal pellets
• willow leaf sawfly (Euura arbusculae) - feeding causes fleshy bumps on leaves

Sawfly lifecycle

Adult sawflies only live for one week, during which time they mate and females lay 30 to 90 eggs. Eggs are tan, oval or kidney-shaped, and look like tiny blisters on the upper surfaces of leaves. In 2 - 8 weeks, depending on temperatures, those eggs hatch and then go through 5 or 6 larval stages, depending on the species, before heading to the soil, en masse, to pupate. Some sawfly species use webspinning and leafrolling to protect their young, while others spin cocoons. The entire process can take 2 years. It is during the larval stages when sawflies do the most damage.

Sawfly damage

Sawflies are defoliators, which means they strip the leaves from several garden plants. Species tend to be host-specific. Rose sawflies attack roses, pine sawflies attack pine trees, and so on. Plants vulnerable to sawfly feeding include apple, cherry, peach, pear, plum, and quince trees, along with most cane fruits.

Larvae often feed in large groups, for added protection. Damage caused by larval forms of sawflies include leafmining, defoliation, skeletonizing, galls, and notching of leaves.

Gall formed by willow leaf sawfly (James Lindsey) CC BY-SA 3.0

Sawfly controls

Generally speaking, handpicking is your best method of controlling sawfly larvae. You can feed them to your chickens for a tasty protein treat, or bag them and toss them in the trash. While Bacillus thuringiensis (Bt) can be used to control moth and butterfly larvae, it is not effective against sawfly larvae.

Insecticides can be used against sawflies, but sawfly larvae are a popular food for many native birds, including partridges, black grouse, corn buntings, and chestnut-backed chickadees. Shrews, lizards and frogs also enjoy snacking on these pests, along with several predatory wasps, including ichneumon and braconid wasps. 

You can attract these garden helpers by providing fresh water, growing a variety of insectary plants and plants that provide pollen and nectar, and avoiding the use of broad spectrum pesticides and herbicides.