The insect that is commonly called a sawfly is actually not a fly!
The common term sawfly refers to over six different families in the Hymenoptera order of bees, ants, and wasp. Sawflies are a member of the Tethredinoidea superfamily and are believed to be quite primitive. In appearance, the sawfly might remind one of a bee or wasp more than a fly.
These confusing little insects can be found in areas throughout the world even though the species will differ depending on where they are found. Confusing one even further, the larva of most species of the sawfly looks very much like the caterpillar larva of the butterfly or moth and feed on plants. Sorting out an insect that is called a fly, looks like a bee or wasp and has larva that resemble that of the butterfly or moth can be difficult without going back in evolutionary time.
There are five families in the Tethredinoidea super family, which consist of the argid sawfly, the conifer sawfly, the typical sawfly, the cimbicid sawfly and the pergid sawfly. Each of these families have hundred of species. Even so, all sawflies are believed to be one of the most primitive of the Hymenoptera order since they are without stingers and have larva that prefer feeding on plants. Some studies have led scientist to believe that most wasps, at one time, fed mainly on plant life. This life of plant feeding led to the development of the ovipositor in females making it possible for her to insert her eggs into a host plant.
When the eggs hatched the larva fed on the host plant which eventually led to the development of certain chemicals showing up in the eggs that created a bitter taste in the insect. As the wasp continued to evolve it is believed they began attaching their eggs to other insects as a means of survival. Studies suggest that while doing this they learned to use the bitter or poisonous chemical from their bodies to inject the host insect, creating a kind of paralysis. It is suggested that this later evolved into the use of the ovipositor as a stinging weapon.
Of all the insects in the Hymenoptera order, the bee is considered to be in the highest order of evolution since it has returned to feeding on plants. It is believed that the sawfly is an early stage of development in the evolution of this insect. Today the sawfly is considered to be more a wasp even though the thorax and abdomen are joined more like that of the fly. It is possible the common name of this insect was derived from the female’s ovipositor, which has saw-like teeth. Adults may be difficult to observe even though they are quite active from spring right through summer.
Female sawflies, once fertilized, deposit their eggs within the leaves of plants favored by their species. This may be pine, elm, popular, willow shrubs or other such plants. The site where the eggs have been deposited can be distinguished by tiny brown marks that are made in rows. When the eggs hatch the larva feed on the plant. Once they reach maturity, the larva will pupate in a small cocoon before emerging as adults in around two weeks.
One of the best ways to distinguish the sawfly larva is by checking their legs. If you look at the softer leg projections the sawfly larva will have more than six while butterfly or moth larva has no more than five. Check the tips of pine needles for the sawfly larva. In most cases, the body will be either green or black.
Each will have either tiny yellow spots or lines along the body and if you frighten them they will raise their body from the leaf in a distinct curve. Most sawfly larva grows to be no larger than one inch in length and in some species the larva are considered to be a pest.