Hymenoptera (Suborder: Symphyta)

Not all caterpillars on trees and shrubs turn into moths or butterflies (Lepidoptera). Many of them belong to the order Hymenoptera, the ants, bees, wasps, and in this case - sawflies. Sawflies are broad-waisted, wasp-like insects whose caterpillars may feed on both coniferous and deciduous plants. On conifers, sawfly caterpillars may mine buds, bore into the pith of shoots, feed on only old or only new needles, or make messy webs. On deciduous or broad-leaved plants, some species of sawflies are defoliators, while others are leaf-rollers, web formers, skeletonizers, leaf or bud miners, stem borers, or gall makers (Johnson and Lyon, 1991). Identification of the host plant, the type of damage seen, and the timing during the growing season can help narrow down which species of insect may be involved. For information about common coniferous sawfly species, see the "Pine Sawflies" section of the Guide or any of the following individual species: European pine sawfly (Neodiprion sertifer), introduced pine sawfly (Diprion similis), pine false webworm (Acantholyda erythrocephala), and redheaded pine sawfly (Neodiprion lecontei). Here, some of the common sawflies found on deciduous host plants are summarized, including: azalea sawfly (Amauronematus azalea), birch sawfly (Arge pectoralis), dogwood sawfly (Macremphytus tarsatus), dusky birch sawfly (Croesus latitarsus), elm leafminer (Fenusa ulmi), maple petiole borer (Caulocampus acericaulis), mountain ash sawfly (Pristiphora geniculata), pear sawfly (Caliroa cerasi), and roseslugs (Endelomyia aethiops and Allantus cinctus). Further detail about each of the individual species mentioned here is available elsewhere in this Guide.

The azalea sawfly (Amauronematus azalea) is one of at least 3 sawfly species known to feed on azalea in the eastern US. Larvae feed on the edges of the leaves of their hosts. One generation occurs per year. These caterpillars are green with an amber colored head and various tiny black spots. Larval development is complete by July 1 in Massachusetts and they grow to approx. 0.39 inch long. Adult females are wasp-like insects that lay their eggs on expanding spring foliage. Once mature, larvae drop to the soil to pupate. Sawfly larvae will feed on the edges of azalea leaves and may defoliate the plant, leaving only midveins behind at times.

The birch sawfly (Arge pectoralis) adults emerge approximately in June and July from overwintering sites as pupae hidden in the ground at the base of their hosts. (In the leaf-litter.) Larvae are active from approximately mid-June into September on host plant foliage. Larvae have a dull orange head capsule and a pale, yellowish-green body with several lines of black spots. The larvae of this sawfly are 0.8-1 inch in length when fully matured. The feeding behavior of this insect may resemble that of other sawfly species found on birch. Larvae may be important defoliators of birch, generally present between mid-June through mid-September. Feeding from this insect is similar to that of Croesus latitarsus, the dusky birch sawfly. The dusky birch sawfly has one or two generations occur per year. Winter is spent as a prepupa in a cocoon in the soil. Pupation occurs in the springtime, and adults emerge in May. Eggs are laid and larvae occur from April-May (1st generation) and again in mid-July to mid-September (2nd generation). Larvae have a black head capsule and are generally yellow in color with black markings and may reach up to an inch in length when fully grown. Larvae sit in an S-posture (rear-end out) when alarmed or not feeding. If there is a second generation, adults may emerge again from mid-July to mid-September. Adults are approximately 1/2 inch in length and look like black wasps.  Foliage of birches, primarily gray birch, but also black, yellow, and paper birches is consumed. Small trees may be defoliated by these caterpillars that feed in groups, particularly around leaf margins. 

The dogwood sawfly (Macremphytus tarsatus) has a single generation per year. The larvae of the dogwood sawfly overwinter in decaying wood and occasionally compromised structural timber. An overwintering "cell" is created in this soft wood. Pupation occurs in the springtime and adults can take a lengthy time to emerge, roughly between late May and July. 100+ eggs are laid in groups on the underside of leaves. Eggs hatch and the larvae feed gregariously, initially skeletonizing leaves. As the caterpillars grow in size, they are capable of eating the entire leaf with the exception of the midvein. Larval appearance varies greatly throughout instars, so much so that one might mistake them for multiple species. Early instars are translucent and yellow, but as the caterpillars grow they develop black spots (over yellow) and become covered in a white powder-like material. Larvae and their shed skins may resemble bird droppings. Full grown larvae begin to wander in search of a suitable overwintering location. Rotting wood lying on the ground is preferred for this. Foliage of dogwood, especially gray dogwood (Cornus racemosa) is fed upon. Skeletonizes leaves at first, then eats all but the midvein.

The elm leafminer (Fenusa ulmi) is a European species that was introduced into the United States prior to 1898. This insect is a leaf mining sawfly whose adults are approximately 3 mm. in length and look like tiny black wasps. In New England, the adult is said to be active in May at which point it lays eggs in host plant leaf tissues through slits cut in the leaf using a saw-like ovipositor (egg laying structure of the females). It takes the eggs approximately 1 week to hatch, and tiny larvae begin to mine blotches in host plant leaves. Mines may appear as tiny, whitish spots confined between leaf lateral veins. Tissues between the two layers of epidermis are eaten. When several mines coalesce, large blotches are formed. By late spring, the larvae have completed their development and will cut their way out of the leaf, drop to the ground, and prepare to pupate in a papery cocoon buried in the soil beneath the host plant. They are thought to remain as pre-pupa through the summer, fall, and winter only to pupate and emerge as adults the following spring. One generation is thought to occur per year.

The maple petiole borer (Caulocampus acericaulis) is a sawfly species that is non-native to the United States and likely an introduction from Europe. It was first reported in 1899 in Danbury, CT (Britton, 1906). The adult sawflies (non-stinging, wasp-like insects) emerge in May and lay their eggs (colorless, long, slender, and curved) at the base of the petiole of their host plant. Adult females have been dissected to reveal that each may have as many as 19 eggs. Adults are rarely seen, but approximately 1/4 inch in length with a shiny, black colored head and thorax and yellow, black tipped abdomen with yellow legs. The larvae feed by mining the leaf petioles, eating almost all of the tissue within. Eventually, this feeding causes the petiole to break, an inch or so from the leaf itself. Leaf drop from the activity of this insect may be noticed in May and June. Feeding occurs approximately over that one month period. While this activity may be concerning, this insect does not normally cause damage to the overall health of the host plant and management is rarely needed. Fully grown larvae are 8 mm in length and resemble weevil larvae (thoracic legs are so small they may appear legless, white in color with brown heads). Larvae do not drop to the ground with the severed leaf portion - they remain in the petiole, which then eventually drops to the ground and contains the larva. Larvae crawl to the soil surface and burrow 5-8 cm below, where they pupate. The pupa is found in a round to oval, earthen cell that is 5 mm. in diameter. Overwintering occurs as a prepupa in the earthen cell. One generation occurs per year. 

The mountain ash sawfly (Pristiphora geniculata) is found in the Northeast as well as parts of Canada, but also occurs in Europe. Historically, scientists were uncertain of its native origin - whether it came from Europe, or not (Johnson and Lyon, 1991). Natural Resources Canada refers to it as a non-native species. Prepupa overwinter, and starting in late-May the adult sawflies emerge from the soil over a period of approximately 6 weeks. Adults may be found into early July. A second generation of adults occurs by mid-August. In each case, the females lay their eggs in the host plant leaves by cutting a slit in the epidermis with their ovipositor (egg laying structure) at the edges of the leaflet. Adult sawflies live for approximately one week. The first generation eggs hatch by early-June and are present until early-August with second generation eggs hatching and larvae found in September. Larvae feed for approximately 3 weeks in groups - stripping branches of all of their foliage before moving on to the next. Caterpillars are at first pale yellow in color, and eventually yellow with black flecks. Caterpillars will rear up, raising their heads, in an "S" shape if disturbed. The oldest caterpillars may eventually feed alone in the tree. Once mature, the caterpillars drop to the soil and create an earthen cell within which they form a paper cocoon to pupate in. The overwintering life stage (the prepupa) is capable of remaining in a diapause (resting) state for multiple years.

The pear sawfly (Caliroa cerasi) is a non-native species introduced from Europe into the United States that feeds on a wide variety of trees and shrubs. Because of the slimy, non-segmented appearance of the immature larvae (caterpillars), these insects are sometimes called slugs. The pear sawfly overwinters in the soil as a mature (fully grown) larva which will undergo pupation in the spring. Adult sawflies emerge from pupation in late-May and June. Adults are glossy black and yellow wasps. Female sawfly adults will lay their 1 mm long, oval, tan eggs one at a time on the underside of the leaf, in a blister-like pocket between the two epidermal layers of the leaf. When eggs hatch, the caterpillars feed initially as skeletonizers on the upper side of the leaf. Young caterpillars are a dark greenish/black color and slimy, lack distinctly visible legs, are approximately 1.4 mm long, and are wider at the front end. Skeletonized leaves turn brown, with premature leaf drop occurring at times. Caterpillars are found feeding on host plant leaves for up to 4 weeks, and pass through 5 instars. Mature caterpillars are yellow, slimy, have 10 pairs of visible legs, and are 1/2 inch long. Upon maturity, caterpillars drop to the ground to form cells within which they pupate in the soil. It is possible for a second generation of adults to emerge by August. Activity of the second generation may continue through September, until the mature larvae of the second generation move to the soil to overwinter.

The term roseslug or roseslugs refers to a couple different species of sawfly caterpillars found on rose. The roseslug (Endelomyia aethiops) may be found on the same plants as the curled rose sawfly (Allantus cinctus). The roseslug, E. aethiops, is found in British Columbia as well as the United States, and is thought to be a native species The roseslug was first identified as a pest in Cambridge, MA in gardens in 1831 (Chittenden, 1908). According to Chittenden, 1908, "By 1840 it had become so great a nuisance that a premium of $100 was offered for the most successful method of destroying it (Harris)". Rose species are their only hosts, and females lay eggs in individual pockets on the edges of leaves. This is done with the female's ovipositor (egg laying device) which cuts a pocket between the leaf surfaces into which the egg is inserted. Hatching occurs 10-14 days after eggs are laid. Newly hatched larvae begin to feed by skeletonizing the upper surfaces of leaves. The roseslug larvae (caterpillars) are approximately 1/2 inch long when mature, and complete their skeletonization feeding at that time, after approximately 5-6 weeks of feeding. During the day, larvae rest on the undersides of leaves. Once ready to pupate, they leave the plant and enter the soil to create a cell within which they overwinter. This species of roseslug's larvae may all be done feeding and in the soil by approximately July. They remain in their winter cells until the following spring, at which time pupation occurs. A single generation of E. aethiops occurs per year. Adults are dark in color (deep, shiny black) and wasp-like with four smokey colored wings. Adult females are approximately 1/5 inch long, with males slightly smaller.

The curled rose sawfly, Allantus cinctus, is approximately 0.75 inch long at the time the caterpillar is fully mature. This species is likely an accidental introduction from Europe, first viewed as a pest near Boston, MA in 1887 (Chittenden, 1908). Because their caterpillars are larger than those of the roseslug, it only takes a few of them to seriously damage plants. The curled rose sawfly does not often occur in large populations, yet for the aforementioned reason they can still be significant pests. Caterpillars of this species not only injure plants by feeding on their leaves, but they also bore into the pith of twigs, which can kill stems and act as an area for fungal pathogens to become introduced. Caterpillars of this species will skeletonize the leaves and are eventually capable of eating the entire leaf except the main vein. Boring into the pith of the twig, especially pruned twigs, occurs when the insect is ready to pupate. It is possible that two generations of the curled rose sawfly can occur per year, and in some locations, three may occur. Caterpillars of this species are green on their backs, with abdomens marked with white spots. The head of the caterpillar is yellow in color with a dark brownish stripe down the middle, and with black eye spots. Caterpillars may be found coiled when at rest. Adults are approximately 3/8 inch long, with nearly transparent wings and a shining black abdomen with a wide band in the middle. Adult emergence occurs some time in May. Eggs are laid singly on leaf undersides in groups of 3-7. Historically, adults had also been observed again in Boston, MA in July (Chittenden, 1908). Other species of sawflies with similar habits may be found on similar host plants in different geographic locations.