Is this a sawfly?
Recognizing adult sawflies
Sawflies look very much like other wasps or bees of the order Hymenoptera. However, sawflies are a diverse group of families that vary greatly in appearance.
There are a few characteristics that all or most sawflies have in common. The characteristic that nearly always sets sawflies apart from wasps and bees is their lack of a narrow constricted "waist", where the thorax and abdomen come together. It can be difficult to see this characteristic in living animals or preserved specimens if they are posed poorly.
sawfly with a wide, non-constricted “waist” (Eriotremex formosanus)
wasps with classically constricted “waists” (Polistes sp. and Vespula pensylvanica)
Another morphological character unique to sawflies are cenchri, hardened lobes on the dorsal hind surface of the thorax. These aren't present in the family Cephidae, but are diagnostic for all other sawfly families.
classic cenchri position for most sawflies (Cimbex americana)
Because variation in appearance of sawflies is high, the best tool for recognizing sawflies is having an idea of the general morphology of each of the 12 families. Some families are wasp-like, with long, smooth, slender bodies (Cephidae, Siricidae), while some are bee-like with stouter, hairier bodies (Cimbicidae). Some are very small and may be mistaken for small bees or flies (Argidae, Pergidae, Diprionidae) or parasitic wasps (Orussidae). See the photos below for an example and brief description of each of the families included in this tool.
Cephidae are small, slender, and shining like a wasp. The antennae are often slightly clubbed. Cephidae are the only sawfly family to have no cenchri (Calameuta clavata).
Siricidae are medium to large with long, cylindrical bodies and distinctly elongated ovipositors. The pronotum is pronounced. Siricidae can be metallic blue in color on all or parts of the body (Eriotremex formosanus).
Cimbicidae are medium to large, robust, and haired. They have wide heads and large, obvious mandibles. The antennae are distinctly clavate (Trichiosoma triangulum).
Argidae are small to medium in size and often have red/orange markings. They have distinctive antennae; both sexes only have a single elongated flagellomere, and in some males (subfamily Sterictiphorinae) this segment is forked so it appears as though 2 pairs of antennae are present (Eriglenum crudum).
Xiphydriidae have slender, cylindrical bodies. They have spherical, shining heads on a long “neck”, separated from the thorax (Xiphydria mellipes).
Pergidae are similar in appearance to Argidae and are represented by a single genus in North America north of Mexico. Acordulecera is small in size and has only 6 antennal segments (Acordulecera dorsalis).
Orussidae are possibly the most morphologically unique sawfly family. They have long, cylindrical bodies and are mostly black in color. The antennae are located extremely low on the face, near the mouthparts (Kulcania mexicanus).
Xyelidae are small to medium sized, often with noticeably long legs. The distinctive antennae have an elongated third segment with the remaining segments thin, thread-like (Megaxyela major).
Pamphiliidae are small to medium-sized and have relatively large heads that appear quadrate when seen from above, often with yellow or orange markings (Onycholyda sitkensis).
Diprionidae are small to medium in size and relatively stout. The antennae are serrate in females and distinctively comb-like in males (Neodiprion fulviceps).
Tenthredinidae are extremely speciose, so there is high variation within the family. They are small to medium in size and have 7-12 antennal segments (Strongylogaster distans).
Anaxyelidae is represented by a single living species, which occurs in western North America. Syntexis libocedrii is slender and cylindrical with white markings surrounding the eyes and a long ovipositor.
Recognizing immature sawflies
Sawfly larvae are easily confused with butterfly or moth larvae (order Lepidoptera) because of similar morphology and similar feeding behavior. Larvae of both groups are generally long and slender, with segmented bodies and round, sclerotized head capsules.
The key feature distinguishing immature Symphyta from Lepidoptera is the legs. The first 3 body segments of the larva have thin, segmented, thoracic legs. The remaining body segments usually have fleshy, stubby appendages known as prolegs. Caterpillars have five or fewer pair, while sawfly larvae have more than six pairs of prolegs. Additionally, caterpillars have small hooks or hairs at the apex of the prolegs, called crochets. Sawflies do not have crochets.
In some cases, such as leaf miners and “slug” sawflies, the prolegs may be difficult to count or even impossible to see. In these specimens, the distinguishing character is the “eyes”, or stemmata on the head capsule. While sawfly larvae only have one pair, Lepidopterans can have many, usually six or more pairs of stemmata on the head capsule.
sawfly larvae: a) classic larval morphology (Abia americana), b) prolegs lacking crochets (Halidamia affinis), c) leaf-mining larvae with difficult-to-count prolegs (Fenusa ulmi), d) “slug” sawfly larvae (Caliroa cerasi)
lepidopteran caterpillars: a) classic larval morphology (Anticarsia gemmatalis), b) several pairs of stemmata on head (Anticarsia gemmatalis), c) prolegs with crochets (Agrotis ipsilon), d) caterpillar with difficult-to-count prolegs (Argyresthia pruniella)