In contrast, most sawfly caterpillars with prolegs have them on abdominal segments 2-7 or 8 and retain the anal claspers. The rarely seen larvae of Mecoptera, the scorpionflies, may have prolegs on segments 1-8. Thus, if one can count and has a reasonable guess as to which folds of abdominal skin makes a segment, then one can usually tell an eruciform (eruca is Latin for caterpillar) larval lepidopteron or mecopteron from a sawfly without any special entomological experience.
The picture above is of a sawfly caterpillar – I know it from the shape of the head capsule and the general Gestalt (I was an entomologist for many years and some of it still sticks with me) - but how many prolegs does it have? At BugGuide, Dave Smith points out that most of the grass-feeding sawflies in North America belong to one of two genera: Dolerus and Pachynematus. Larvae of the former have an asymmetrical labrum and prolegs on segment-8; the latter have a symmetrical labrum and no prolegs on segment-8. Alas, neither the labrum nor the prolegs are visible and this id is stuck at my doleful level of Gestalt.