Sawfly Insect Control: How To Get Rid Of Sawflies
By: Jackie Carroll
Sawflies get their name from the saw-like appendage at the tip of their body. Female sawflies use their “saw” to insert eggs into leaves. They are more closely related to wasps than flies, though they don’t sting. Sightings of adult sawflies are rare, but you may occasionally see them near flowers and flower buds where their offspring cause damage to the foliage. Keep reading for more sawfly information.
There are several types of sawflies and most are named for the type of plant on which they feed. Here are a few types that you may find in your landscape:
- Currant sawfly larvae have green or tan spots and they strip the foliage off of currant plants.
- There are a number of different conifer sawflies that can seriously injure their chosen species by feeding on needles and tunneling into buds and shoots.
- Pear and cherry sawfly larvae skeletonize the leaves of their chosen species.
- Pecan sawflies leave holes of different sizes in pecan tree leaves.
- Willow leaf sawfly damage is easily recognized by the fleshy galls that develop at the spot where the female injects her eggs into the leaves.
Sawfly damage is caused by the larvae that feed on the plants in several different ways, depending on the species. Some leave holes or notches in the leaves, while others skeletonize the leaves by completely devouring the tissue between the veins. They may roll up the leaves or spin webs. A few species leave galls on the foliage.
A light infestation may cause only a little cosmetic damage that is easily removed through pruning, while a large number of sawflies can seriously damage or even kill a tree.
How to Get Rid of Sawflies
The control of sawflies is directed at the feeding larvae. Each species of sawfly has its own distinct appearance and habit, and they change their appearance as they develop. Although a few species of sawfly have larvae that resemble slugs, most look like caterpillars. It’s important to learn the difference between sawfly larvae and caterpillars because the insecticides used to kill caterpillars have no effect on sawfly larvae.
The easiest way to tell the difference between sawfly larvae and caterpillars is to look at the legs. Sawfly larvae have three pairs of true legs, followed by seven or eight pairs of fleshy, false legs. Caterpillars have five or fewer pairs of false legs that are armed with tiny hooks.
Handpicking may be the only control measure you need to control light infestations. Sawflies have several natural enemies that keep them in check, including predatory beetles, parasitic wasps, and viral and fungal diseases. Avoid using broad spectrum insecticides that will damage the beneficial insect population. Good choices that are effective, but have little environmental impact, include insecticidal soaps and narrow-range oils.
Another aspect of sawfly insect control is directed at the pupa that overwinter in cocoons in the soil. Cultivating the soil exposes them to freezing weather and birds that feed on them. Cultivate the soil several times over the winter months, taking care not to damage the roots of dormant plants.
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Sawfly, Genus Perga Image: Andrew Donnelly © Australian Museum " > Click to enlarge image Toggle Caption
- Classification Suborder Symphyta Order Hymenoptera Phylum Arthropoda Kingdom Animalia Number of Species 176 Size Range Wingspan 2 cm – 4 cm
Sawfly larvae feeding on a eucalyptus leaf.
Image: Yazmin Tresize
© Yazmin Tresize
Sawflies are probably closest to the ancestral form that all hymenopterans (ants, wasps, bees and sawflies) evolved from. However, they are placed in a separate suborder, Symphyta (ants, bees and wasps belong to the suborder Apocrita) based on reproductive and other characteristics.
Sawflies do not possess the distinctive thin waist of the other hymenopterans, nor do they possess a sting. Their name comes from the female's saw-like egg-laying tube, which she uses to make a slit in a plant leaf or stem, into which she lays her eggs. The adult Steel-Blue Sawfly is usually a dark metallic blue, with a white spot on the thorax, and has a wingspan of about 4cm. The adult Bottlebrush Sawfly has an orange and black banded body, with a wingspan of about 2cm. Males have feathery (pectinate) antennae.
Found on native trees and shrubs, such as eucalypts, paperbarks and bottlebrushes.
Feeding and diet
Sawfly larvae feed mainly on native trees and shrubs, such as eucalypts, paperbarks and bottlebrushes, although a small number of species are parasitic.
Larvae of sawfly species that feed upon eucalypts are often seen during the day in large closely packed groups on branches or on the ground. These larvae can cause extensive damage to their food plants. One very destructive genus is the Steel-Blue Sawfly (Perga sp.) which attacks eucalypts in south-eastern Australia. These larvae secrete an irritating or distasteful liquid from their mouths. With this defence, the sawfly larvae are usually avoided by predators. They are sometimes called 'spitfires', although they don't actually spit.
Melaleuca and Callistemon feeders
Sawflies are also found on Paperbarks (Melaleuca). A commonly occurring species is Pterygophorus facielongus, sometimes called the Long-tailed Sawfly. Unlike Steel-blue Sawflies, Long-tailed Sawfly larvae do not cluster in large numbers, but may sometimes cluster in small groups in the daytime. One of their favourite food plants is Melaleuca armillaris. At first the small larvae skeletonise leaves. The larger larvae eat whole leaves and can strip all the leaves from the top of the crown, feeding during both day and night.
The Bottlebrush Sawfly is another species of Pterygophorus, P. cinctus, which feeds on Bottlebrush (Callistemon).
The sawfly's name comes from its ovipositor (or egg laying tube), which is saw-like. The female sawfly uses this ovipositor to saw a slit in plant leaves and stems, into which she then lays her eggs. The larvae of the Steel-Blue Sawfly pupate in a cocoon in the leaf litter, while Bottlebrush Sawflies pupate without a cocoon. When Long-tailed Sawfly larvae have finished feeding, they enter a mobile pre-pupal stage, seeking soft bark (such as a paperbark trunk) or soft timber in which to bore and pupate.
Danger to humans
Adult sawflies are not capable of stinging. However, the larvae may secrete an irritating liquid onto the skin or into eyes if disturbed.
- Size: Sawfly adults are about 1/2 inch long.
- Characteristics: Sawflies may look like flies, but are actually related to bees and wasps. The common name sawfly comes from their ovipositor, which is saw-like in shape and is used by the females to cut into the plants and lay eggs.
- Body: They have four wings (flies have two,) and unlike many wasps, sawflies do not have the thin segment between the thorax and abdomen.
How Did I Get Sawflies?
Homes surrounded by trees and landscaping are prone to a sawfly infestation. The insects don't normally enter houses, but larvae may fall into open doors and windows from branches close to buildings. Adults can also fly inside through the same openings. Sawflies are not actually flies, but are in the same insect group as bees, wasps, and ants.
How Serious Are Sawflies?
These pests aren't an issue indoors, and unlike other wasps, females do not sting. However, infestations can affect outdoor trees. While they are usually benign, some species with large populations produce serious economic damage to large forests and cultivated plant acreages.
Larvae feeding habits can slow or stop plant growth, weaken leaves, and wilt stems. Both mature and larval sawflies are harmless to humans. Sawflies infest many species of trees and a large infestation may weaken a tree’s ability to withstand damage caused by other tree infesting insects.
How Do I Get Rid of Sawflies?
Keeping your trees and plants healthy. Plants that are young and in poor health are likely to experience more injury and damage than healthy plants. If practical, you can also hand pick sawfly larvae from your plants.
Grown trees and shrubs can withstand moderate sawfly defoliation without experiencing reduced growth or mortality. This is due to the abundance of predators such as wasps and beetles, plus the occurrence of fungal and viral diseases that often kill off sawfly populations. So, it is not wise to use conventional insecticides that will kill their predators.
What Orkin Does
If you need help with a sawfly infestation, seek the assistance of your pest management professional rather than relying on do-it-yourself procedures. Some other components of an effective sawfly management program include:
- Inspection: Frequently inspect plants for sawfly damage. The earlier you find sawflies, the easier it will be to manage the population and prevent damage to your trees or shrubs.
- Identification:Asking your pest management professional to identify any insect specimens to ensure that the correct control options are used. Your pest management professional can also advise you whether it is worthwhile to apply a conventional insecticide for sawfly control.
Your local Orkin technician is trained to help manage sawflies and similar pests. Since every building or home is different, your Orkin technician will design a unique program for your situation.
Orkin can provide the right solution to keep sawflies in their place…out of your home, or business.
Behavior, Diet, Habits
Since there are so many different species of sawfly, their preferred host plants vary a great deal. Most coniferous feeding sawflies eat the tree’s needles and buds. Deciduous feeders will skeletonize, mine, or chew holes in the leaves. Sawflies feed on a wide variety of:
- Coniferous & Deciduous Trees
The sawfly larval stages are plant feeders and look much like the caterpillar of butterflies and moths. Sawfly larvae will either feed inside or on the outside surface of plant leaves and stems or inside a gall that is produced when the female stings the plant leaf or stem. Sawflies usually have one generation per year and spend the winter months in the larval or pupal stages.
Sawfly Information - Learn About The Control Of Sawflies - garden
Dogwood sawfly, Macremphytus tarsatus, has been found on shrubby dogwood species on campus. While this pest looks like a caterpillar, it is actually the larval stage of a wasp-like Hymenoptera species.
Adult sawflies emerge in late spring and lay their eggs on the undersides of leaves. When the eggs hatch in mid-summer, the first stage larvae are tiny, yellow, and translucent. As they grow and molt, they become covered with a white waxy coating. They usually spend the daylight hours curled up and clinging to the underside of leaves. They can be quite gregarious, with a dozen or more congregating on one leaf. In large numbers, they can cause considerable defoliation and while unsightly, it usually will not harm the plant because it is late in the season. After the last molt, they usually stop feeding and seek a protected spot to overwinter. In early spring, they will pupate and later emerge as adults.
Leaf damage on shrubby dogwood. photo credit: W. Costello
The best control method is to handpick and drop them into a container of soapy water. You can also squash them under foot if you are so inclined (messy but effective.)
Occasionally, wasps or hornets will attack the larvae, which is fascinating to watch. They usually chew the sawfly in half and fly them back to their nest.
Dogwood sawfly on the underside of the leaf. photo credit: W. Costello
When the sawfly is detected early, insecticidal soap or horticultural oil is an effective control. In large plantings, chemical controls may be required. When the sawflies are larger, one of the contact or systemic insecticides registered for control may be needed.
- 1 Etymology
- 2 Phylogeny
- 2.1 Taxonomy
- 3 Description
- 4 Distribution
- 5 Behaviour and ecology
- 5.1 Parasites
- 5.2 Life cycle and reproduction
- 5.2.1 Life cycle of Cladius difformis (bristly rose slug)
- 6 Relationship with humans
- 7 References
- 7.1 Bibliography
- 8 Further reading
- 9 External links
- 9.1 General
- 9.2 Taxonomy
The suborder name "Symphyta" derives from the Greek word symphyton, meaning "grown together", referring to the group's distinctive lack of a wasp waist between prostomium and peristomium.  Its common name, "sawfly", derives from the saw-like ovipositor that is used for egg-laying, in which a female makes a slit in either a stem or plant leaf to deposit the eggs.  The first known use of this name was in 1773.  Sawflies are also known as "wood-wasps". 
In his original description of Hymenoptera in 1863, German zoologist Carl Gerstäcker divided them into three groups, Hymenoptera aculeata, Hymenoptera apocrita and Hymenoptera phytophaga.  But four years later in 1867, he described just two groups, H. apocrita syn. genuina and H. symphyta syn. phytophaga.  Consequently, the name Symphyta is given to Gerstäcker as the zoological authority. In his description, Gerstäcker distinguished the two groups by the transfer of the first abdominal segment to the thorax in the Apocrita, compared to the Symphyta. Consequently, there are only eight dorsal half segments in the Apocrita, against nine in the Symphyta. The larvae are distinguished in a similar way. 
The Symphyta have therefore traditionally been considered, alongside the Apocrita, to form one of two suborders of Hymenoptera.   Symphyta are the more primitive group, with comparatively complete venation, larvae that are largely phytophagous, and without a "wasp-waist", a symplesiomorphic feature. Together, the Symphyta make up less than 10% of hymenopteran species.  While the terms sawfly and Symphyta have been used synonymously, the Symphyta have also been divided into three groups, true sawflies (phyllophaga), woodwasps or xylophaga (Siricidae), and Orussidae. The three groupings have been distinguished by the true sawflies' ventral serrated or saw-like ovipositor for sawing holes in vegetation to deposit eggs, while the woodwasp ovipositor penetrates wood and the Orussidae behave as external parasitoids of wood-boring beetles. The woodwasps themselves are a paraphyletic ancestral grade. Despite these limitations, the terms have utility and are common in the literature. 
While most hymenopteran superfamilies are monophyletic, as is Hymenoptera, the Symphyta has long been seen to be paraphyletic.   Cladistic methods and molecular phylogenetics are improving the understanding of relationships between the superfamilies, resulting in revisions at the level of superfamily and family.  The Symphyta are the most primitive (basal) taxa within the Hymenoptera (some going back 250 million years), and one of the taxa within the Symphyta gave rise to the monophyletic suborder Apocrita (wasps, bees, and ants).   In cladistic analyses the Orussoidea are consistently the sister group to the Apocrita.  
The oldest unambiguous sawfly fossils date back to the Middle or Late Triassic. These fossils, from the family Xyelidae, are the oldest of all Hymenoptera.  One fossil, Archexyela ipswichensis from Queensland is between 205.6 and 221.5 million years of age, making it among the oldest of all sawfly fossils.  More Xyelid fossils have been discovered from the Middle Jurassic and the Cretaceous, but the family was less diverse then than during the Mesozoic and Tertiary. The subfamily Xyelinae were plentiful during these time periods, in which Tertiary faunas were dominated by the tribe Xyelini these are indicative of a humid and warm climate.   
The cladogram is based on Schulmeister 2003.  
There are approximately 8,000 species of sawfly in more than 800 genera, although new species continue to be discovered.    However, earlier studies indicated that 10,000 species grouped into about 1,000 genera were known.  Early phylogenies such as that of Alexandr Rasnitsyn, based on morphology and behaviour, identified nine clades which did not reflect the historical superfamilies.  Such classifications were replaced by those using molecular methods, starting with Dowton and Austin (1994).  As of 2013, the Symphyta are treated as nine superfamilies (one extinct) and 25 families. Most sawflies belong to the Tenthredinoidea superfamily, with about 7,000 species worldwide. Tenthredinoidea has six families, of which Tenthredinidae is by far the largest with some 5,500 species.  
Extinct taxa are indicated by a dagger (†).
- Superfamily TenthredinoideaLatreille, 1803 (6 & †2 families)
- Family ArgidaeKonow, 1890 (58 genera, 897 spp.) and †1 genus
- Family BlasticotomidaeThomson, 1871 (2 genera, 12 spp.) & †1 genus
- Family CimbicidaeW. Kirby, 1837 (16 genera, 182 spp.) & †6 genera
- Family DiprionidaeRohwer, 1910 (11 genera, 136 spp.) & †2 genera
- Family PergidaeRohwer, 1911 (60 genera, 442 spp.)
- Family TenthredinidaeLatreille, 1803 (400 genera, 5,500 spp.) & †14 genera
- Superfamily XiphydrioideaLeach, 1819
- Family XiphydriidaeLeach, 1819 (28 genera, 146 spp.)
- Superfamily Xyeloidea Newman, 1834
- Family Xyelidae Newman, 1834 (5 genera, 63 spp.) & †47genera
Many species of sawfly have retained their ancestral attributes throughout time, specifically their plant-eating habits, wing veins and the unmodified abdomen, where the first two segments appear like the succeeding segments.  The absence of the narrow wasp waist distinguishes sawflies from other members of hymenoptera, although some are Batesian mimics with coloration similar to wasps and bees, and the ovipositor can be mistaken for a stinger.  Most sawflies are stubby and soft-bodied, and fly weakly.  Sawflies vary in length: Urocerus gigas, which can be mistaken as a wasp due to its black-and-yellow striped body, can grow up to 20 mm ( 3 ⁄4 in) in length, but among the largest sawflies ever discovered was Hoplitolyda duolunica from the Mesozoic, with a body length of 55 mm ( 2 1 ⁄4 in) and a wingspan of 92 mm ( 3 1 ⁄2 in).   The smaller species only reach lengths of 2.5 mm ( 3 ⁄32 in). 
Heads of sawflies vary in size, shape and sturdiness, as well as the positions of the eyes and antennae. They are characterised in four head types: open head, maxapontal head, closed head and genapontal head. The open head is simplistic, whereas all the other heads are derived.  The head is also hypognathous, meaning that the lower mouthparts are directed downwards. When in use, the mouthparts may be directed forwards, but this is only caused when the sawfly swings its entire head forward in a pendulum motion.  Unlike most primitive insects, the sutures (rigid joints between two or more hard elements on an organism) and sclerites (hardened body parts) are obsolescent or absent. The clypeus (a sclerite that makes up an insects "face") is not divided into a pre- and postclypeus, but rather separated from the front.  The antennal sclerites are fused with the surrounding head capsule, but these are sometimes separated by a suture. The number of segments in the antennae vary from six in the Accorduleceridae to 30 or more in the Pamphiliidae.  The compound eyes are large with a number of facets, and there are three ocelli between the dorsal portions of the compound eyes.  The tentorium comprises the whole inner skeleton of the head. 
Three segments make up the thorax: the mesothorax, metathorax and prothorax, as well as the exoskeletal plates that connect with these segments.  The legs have spurs on their fourth segments, the tibiae.  Sawflies have two pairs of translucent wings. The fore and hind wings are locked together with hooks.  Parallel development in sawfly wings is most frequent in the anal veins. In all sawflies, 2A & 3A tend to fuse with the first anal vein. This occurs in several families including Argidae, Diprionidae and Cimbicidae. 
The larvae of sawflies are easily mistaken for lepidopteran larvae (caterpillars). However, several morphological differences can distinguish the two: while both larvae share three pairs of thoracic legs and an apical pair of abdominal prolegs, lepidopteran caterpillars have four pairs of prolegs on abdominal segments 3-6 while sawfly larvae have five pairs of prolegs located on abdominal segments 2–6 crochets are present on lepidopteran larvae, whereas on sawfly larvae they are not the prolegs of both larvae gradually disappear by the time they burrow into the ground, therefore making it difficult to distinguish the two and sawfly larvae only have a single pair of minute eyes, whereas lepidopteran larvae have four to six eyes on each side of the head.   Sawfly larvae behave like lepidopteran larvae, walking about and eating foliage. Some groups have larvae that are eyeless and almost legless these larvae make tunnels in plant tissues including wood.  Many species of sawfly larvae are strikingly coloured, exhibiting colour combinations such as black and white while others are black and yellow. This is a warning colouration because some larvae can secrete irritating fluids from glands located on their undersides. 
Sawflies are widely distributed throughout the world.  The largest family, the Tenthredinidae, with some 5,000 species, are found on all continents except Antarctica, though they are most abundant and diverse in the temperate regions of the northern hemisphere they are absent from New Zealand and there are few of them in Australia. The next largest family, the Argidae, with some 800 species, is also worldwide, but is commonest in the tropics, especially in Africa, where they feed on woody and herbaceous angiosperms. Of the other families, the Blasticotomidae and Megalodontidae are Palearctic the Xyelidae, Pamphilidae, Diprionidae, Cimbicidae, and Cephidae are Holarctic, while the Siricidae are mainly Holarctic with some tropical species. The parasitic Orussidae are found worldwide, mostly in tropical and subtropical regions. The wood-boring Xiphydriidae are worldwide, but most species live in the subtropical parts of Asia. 
Sawflies are mostly herbivores, feeding on plants that have a high concentration of chemical defences. These insects are either resistant to the chemical substances, or they avoid areas of the plant that have high concentrations of chemicals.  The larvae primarily feed in groups they are folivores, eating plants and fruits on native trees and shrubs, though some are parasitic.    However, this is not always the case Monterey pine sawfly (Itycorsia) larvae are solitary web-spinners that feed on Monterey pine trees inside a silken web.  The adults feed on pollen and nectar. 
Sawflies are eaten by a wide variety of predators. While many birds find the larvae distasteful, some such as the currawong (Strepera) and stonechats (Saxicola) eat both adults and larvae.   The larvae are an important food source for the chicks of several birds, including partridges.  Sawfly and moth larvae form one third of the diet of nestling corn buntings (Emberiza calandra), with sawfly larvae being eaten more frequently on cool days.  Black grouse (Tetrao tetrix) chicks show a strong preference for sawfly larvae.   Sawfly larvae formed 43% of the diet of chestnut-backed chickadees (Poecile rufescens).  Small carnivorous mammals such as the masked shrew (Sorex cinereus), the northern short-tailed shrew (Blarina brevicauda) and the deer mouse (Peromyscus maniculatus) predate heavily on sawfly cocoons.  Insects such as ants and certain species of predatory wasps (Vespula vulgaris) eat adult sawflies and the larvae, as do lizards and frogs.   Pardalotes, honeyeaters and fantails (Rhipidura) occasionally consume laid eggs, and several species of beetle larvae prey on the pupae. 
The larvae have several anti-predator adaptations. While adults are unable to sting, the larvae of species such as the spitfire sawfly regurgitate a distasteful irritating liquid, which makes predators such as ants avoid the larvae.   In some species, the larvae cluster together, reducing their chances of being killed, and in some cases form together with their heads pointing outwards or tap their abdomens up and down.   Some adults bear black and yellow markings that mimic wasps. 
Sawflies are hosts to many parasitoids, most of which are parasitic Hymenoptera more than 40 species are known to attack them. However, information regarding these species is minimal, and fewer than 10 of these species actually cause a significant impact on sawfly populations.  Many of these species attack their hosts in the grass or in other parasitoids. [ clarification needed ] Well known and important parasitoids include Braconidae, Eulophidae and Ichneumonidae wasps. Braconid wasps attack sawflies in many regions throughout the world, in which they are ectoparasitoids, meaning that the larvae live and feed outside of the hosts body braconids have more of an impact on sawfly populations in the New World than they do in the Old World, possibly due to no known ichneumonid parasitoids living in North America. [ clarification needed ] Some braconid wasps that attack sawflies include Bracon cephi, B. lisogaster, B. terabeila and Heteropilus cephi.    Female braconids locate sawfly larvae through the vibrations they produce when feeding, followed by inserting the ovipostior and paralysing the larva before laying eggs inside the host. These eggs hatch inside the larva within a few days, where they feed on the host. The entire host's body may be consumed by the braconid larvae, except for the head capsule and epidermis. The larvae complete their development within two or three weeks. 
Ten species of wasps in the family Ichneumonidae attack sawfly populations, although these species are usually rare. The most important parasitoids in this family are species in the genus Collyria. Unlike Braconid wasps, the larvae are endoparasitoids, meaning that the larvae live and feed inside the hosts body.  One well known Ichneumonid is Collyria coxator, which is a dominant parasitoid of C. pygmaeus. Recorded parasitism rates in Europe are between 20 – 76%, and as many as eight eggs can be found in a single larva, but only one Collyria individual will emerge from its host. The larva may remain inside of their host until spring, where it emerges and pupates. 
Several species in the family Eulophidae attack sawflies, although their impact is low. Two species in the genus Pediobius have been studied the two species are internal larval parasitoids and have only been found in the northern hemisphere. Parasitism of sawflies by Eulophids in grass exceeds 50%, but only 5% in wheat. It is unknown as to why the attack rate in wheat is low.  Furthermore, some fungal and bacterial diseases are known to infect eggs and pupa in warm wet weather. 
Outbreaks of certain sawfly species, such as Diprion polytomum, have led scientists to investigate and possibly collect their natural enemies to control them. Parasites of D. polytomum have been extensively investigated, showing that 31 species of hymenopterous and dipterous parasites attack it. These parasites have been used in successful biological control against pest sawflies, including Cephus cinctus throughout the 1930s and 1950s and C. pygmaeus in the 1930s and 1940s.  
Life cycle and reproduction Edit
Like all other hymenopteran insects, sawflies go through a complete metamorphosis with four distinct life stages – egg, larva, pupa and adult.  Many species are parthenogenetic, meaning that females do not need fertilization to create viable eggs. Unfertilized eggs develop as male, while fertilized eggs develop into females (arrhenotoky). The lifespan of an individual sawfly is two months to two years, though the adult life stage is often very short (approximately 7 – 9 days), only long enough for the females to lay their eggs.    The female uses its ovipositor to drill into plant material to lay her eggs (though the family Orussoidea lay their eggs in other insects). Plant-eating sawflies most commonly are associated with leafy material but some specialize on wood, and the ovipositors of these species (such as the family Siricidae) are specially adapted for the task of drilling through bark. Once the incision has been made, the female will lay as many as 30 to 90 eggs. Females avoid the shade when laying their eggs because the larvae develop much slower and may not even survive, and they may not also survive if they are laid on immature and glaucous leaves. Hence, female sawflies search for young adult leaves to lay their eggs on.  
These eggs hatch in two to eight weeks, but such duration varies by species and also by temperature. Until the eggs have hatched, some species such as the small brown sawfly will remain with them and protects the eggs by buzzing loudly and beating her wings to deter predators. There are six larval stages that sawflies go through, lasting 2 – 4 months, but this also depends on the species. When fully grown, the larvae emerge from the trees en masse and burrow themselves into the soil to pupate. During their time outside, the larvae may link up to form a large colony if many other individuals are present. They gather in large groups during the day which gives them protection from potential enemies, and during the night they disperse to feed. The emergence of adults takes awhile, with some emerging anywhere between a couple months to 2 years. Some will reach the ground to form pupal chambers, but others may spin a cocoon attached to a leaf. Larvae that feed on wood will pupate in the tunnels they have constructed. In one species, the jumping-disc sawfly (Phyllotoma aceris) forms a cocoon which can act like a parachute. The larvae live in sycamore trees and do not damage the upper or lower cuticles of leaves that they feed on. When fully developed, they cut small perforations in the upper cuticle to form a circle. After this, they weave a silk hammocks within the circle this silk hammock never touches the lower cuticle. Once inside, the upper-cuticle's disc separates and descends towards the surface with the larvae attaching themselves to the hammock. Once they reach the round, the larvae work their way into a sheltered area by jerking their discs along.  
The majority of sawfly species produce a single generation per year, but others may only have one generation every two years. Most sawflies are also female, making males rare. 
Sawfly Larvae Look Like Caterpillars
Gardeners most often encounter sawflies when the larvae feed on their plants. At first glance, you might think you've got a caterpillar problem, but sawflies have behavioral and morphological differences that differentiate them from Lepidopteran larvae. If the larvae are all feeding along the leaf margins, and rear up their hind ends when disturbed, those are good signs that your pests are sawflies. Keep in mind that pest control products labeled for caterpillars, such as Bt, will not work on sawfly larvae.