Identification
Physical Characteristics
Size: Adult sawfly size varies greatly by species, ranging from 5mm to over 20mm. The Steel-blue Sawfly (Perga affinis) adult is robust, around 20mm long. The larvae are caterpillar-like and can grow up to 80mm in length depending on the species; spitfire larvae commonly reach 50-70mm before pupating.
Coloration: Adult coloration is diverse. The Steel-blue Sawfly adult is a glossy, metallic blue-black or black, often with yellow markings. Other species can be black, brown, or yellow. The larvae are also varied; spitfire larvae are typically black or dark bluish-grey with small white spots, and have a yellowish underside. Bottlebrush sawfly larvae are often green with dark stripes.
Key Features: Adults: No 'waist'. Larvae: Caterpillar-like but with more than 5 pairs of abdominal prolegs. The 'spitfire' larvae of Perga are famous for clustering in large groups during the day.
Biology & Lifecycle
Development & Reproduction
Reproduction Rate: Reproduction is moderate to high, with each female capable of laying many dozens of eggs.
Lifecycle Details
Egg Stage
The lifecycle begins when the adult female uses her specialized, saw-like ovipositor to cut small slits or pockets into the host plant's tissue, typically within leaves or young stems. She then deposits her eggs inside these protected incisions. This method of egg-laying protects the eggs from predators and desiccation. A female may lay several dozen to over a hundred eggs, often in distinct clusters or rows depending on the species. The eggs develop within the plant tissue for several weeks before hatching.
Larval Stage
This is the primary feeding and destructive stage. Upon hatching, the caterpillar-like larvae emerge and begin to feed on the foliage of their host plant. Many Australian species, like the Steel-blue Sawfly, are gregarious, meaning the larvae live and feed together in large, conspicuous groups. They will systematically strip leaves, often moving as a united front from one branch to another. The larval stage involves several instars, where the larva moults its skin to grow larger. This stage can last from one to several months, during which they can cause significant defoliation.
Pupal Stage
Once fully grown, the larvae cease feeding and begin their journey to pupate. Many species, including the spitfires, will crawl or drop down from the host tree to the ground. They then burrow into the soil or leaf litter and spin a tough, durable cocoon made of silk mixed with soil particles and saliva. This cocoon is often dark, leathery, and provides excellent protection. The larva then transforms into a pupa inside this case. This stage can last for several months, and in some species, the prepupal larva can remain dormant inside the cocoon for several years (a state called diapause), waiting for favourable conditions before pupating.
Adult Stage
After the metamorphosis is complete, the winged adult sawfly emerges from the pupal cocoon, often triggered by rainfall. The adults are typically short-lived, with a lifespan of only a week or two. Their primary purpose is to reproduce. They do not cause any feeding damage to plants; many adults feed on nectar and pollen, while some may not feed at all. After mating, the female seeks out a suitable host plant to lay her eggs, starting the cycle anew.
Reproduction Rate
Reproduction is moderate to high, with each female capable of laying many dozens of eggs.
Generations Per Year
Most Australian sawfly species, including Perga, have only one generation per year. However, some smaller species may have two or more generations, particularly in warmer climates.
Development Time
The entire lifecycle is typically annual. The larval stage is active in autumn and winter, with pupation occurring in spring and adults emerging in summer or autumn to mate and lay eggs for the next generation.
Seasonal Cycle
A distinct annual cycle is common. For spitfires, larvae are present through autumn and winter, pupation happens in spring, and adults emerge in summer/autumn.
Environmental Factors
The availability of a specific host plant is the most critical factor. Rainfall can trigger the mass emergence of adults from their cocoons, leading to synchronized egg-laying events.
Habitat & Distribution
Preferred Habitats
- Eucalyptus woodlands and forests are the primary habitat for the most common Australian sawflies (Perga spp.).
- Suburban gardens and parklands that contain suitable host trees, such as eucalypts, bottlebrushes, and paperbarks.
- They are entirely dependent on the presence of their specific host plants.
- Different sawfly species are specialized for different native plants.
- Pine plantations can be attacked by introduced species of wood wasps (a type of sawfly).
Distribution Patterns
Australian Distribution
Native sawflies are found in all states and territories of Australia, wherever their host plants grow. The Steel-blue Sawfly is particularly common throughout the eastern and southern states.
Climate Zones
- Tropical
- Subtropical
- Temperate
- Mediterranean
Urban vs Rural Distribution
Common in both urban and rural settings. They are a familiar sight in suburban gardens with gum trees, as well as in commercial forests and national parks.
Native Range
Australia has a rich and diverse native sawfly fauna, with the family Pergidae being particularly dominant.
Introduced Range
Some sawfly species, like the Sirex Wood Wasp (Sirex noctilio), have been introduced to Australia from overseas and have become major pests of pine plantations.
Introduction History
The pest Sirex Wood Wasp was first detected in Tasmania in the 1950s and has since spread to mainland pine plantations.
Current Spread
Native sawfly populations are widespread and generally stable, though they can have outbreak years. Introduced pest species are subject to ongoing monitoring and control programs.
Limiting Factors
Distribution is strictly limited by the range of their host plants. They are also controlled by a range of natural enemies, including birds, predatory insects, and parasitic wasps.
Behavior & Diet
Activity Pattern
Adults are diurnal, active during the day when they fly, feed on nectar, and search for mates and egg-laying sites. The larvae are active both day and night but are most conspicuous during the day when they are often seen in their tight clusters on branches. They may move to different parts of the tree to feed during the night.
Dietary Preferences
Feeding Habits
Larvae are herbivorous and are typically specialist feeders, consuming the foliage of only one or a few related plant species.
Health Risks
Always consult healthcare professionals for medical concerns related to pest exposure.
Disease Transmission
- Sawflies do not transmit any diseases to humans.
Allergens and Respiratory Issues
The regurgitated fluid from 'spitfire' larvae can be irritating to the skin and eyes. While not a true allergen, direct contact can cause mild contact dermatitis or a stinging sensation in sensitive individuals. It is best to avoid handling them.
Contamination Risk
None.
Vulnerable Populations
- Children, who may be curious and try to touch the larval clusters.
- Individuals with sensitive skin may experience a more pronounced reaction to the regurgitated fluid.
Symptoms of Exposure
- Skin contact with the larval secretion may cause redness, itching, or a mild burning sensation.
- If the fluid gets in the eyes, it can cause significant irritation, stinging, and watering. The eyes should be flushed thoroughly with water.
- There are no long-term health effects.
Transmission Methods
- Direct physical contact with the defensive fluid regurgitated by the larvae.
Risk Severity
Low. Adult sawflies are completely harmless and cannot sting. The primary health concern is minor skin or eye irritation from the larval defensive secretions.
Economic Impact
Treatment Costs
Professional Treatment
For large ornamental trees, professional treatment by an arborist could cost $200-$500. In forestry, costs are part of larger pest management programs.
Prevention Costs
Minimal, focused on monitoring.
Diy Treatment
$20-$60 for horticultural oils, soaps, or manual removal tools.
Property Damage
Structural Damage
None from common leaf-eating sawflies. However, the introduced Sirex Wood Wasp larva bores into pine trees, causing significant structural damage to the timber.
Garden Damage
The primary damage is aesthetic. Heavy infestations of larvae can completely defoliate small to medium-sized ornamental trees, such as eucalyptus or bottlebrush, making them look very unsightly. While healthy trees usually recover, severe defoliation can stress the tree.
Food Contamination
None.
Equipment Damage
None.
Business Impact
Restaurant Issues
None, unless a heavily infested tree is part of an outdoor dining area, which could be an aesthetic concern.
Retail Impact
Nurseries that sell host plants like eucalypts may occasionally have issues with sawfly larvae on their stock.
Reputation Damage
None.
Operational Disruption
Significant disruption and economic loss in commercial pine plantations due to the Sirex Wood Wasp, which degrades timber quality and can kill trees.
Agricultural Impact
Crop Damage
Native sawflies can cause significant defoliation in commercial Eucalyptus plantations grown for timber or essential oils.
Yield Loss
In forestry, defoliation slows tree growth, leading to yield loss. Damage from wood-boring sawflies (Sirex) can make timber unusable.
Beneficial Aspects
Adult sawflies can be pollinators. The larvae are a food source for native birds and other predators. In a natural ecosystem, their feeding is a form of natural pruning.
Economic Loss
Can be significant in specific industries like forestry and eucalyptus oil production. The biological control program for the Sirex Wood Wasp is a major ongoing expense.
Indirect Costs
Healthcare Costs
None.
Cleanup Costs
Minimal, perhaps cleaning up the sticky larval secretions if they drip onto paths.
Replacement Costs
Potential cost of replacing a valuable ornamental tree if it dies from repeated severe defoliation.
Detection & Signs
Visual Signs
- The most obvious sign is seeing the dense clusters of caterpillar-like larvae on the branches and leaves of a host tree.
- Rapid defoliation of branches, with leaves being chewed or completely stripped.
- Seeing skeletonized leaves, where only the tough veins are left behind.
- The presence of the wasp-like adult sawflies flying around the host plant, although they are less commonly noticed.
Physical Evidence
- Large quantities of frass (larval droppings), which look like dark pellets, accumulating on the ground beneath the infested tree.
- The sticky, eucalyptus-smelling fluid ('spit') on leaves or dripping onto surfaces below a cluster of 'spitfire' larvae.
- Finding the tough, dark, leathery cocoons in the soil when digging around the base of a previously infested tree.
Behavioral Signs
- The coordinated defensive rearing-up and regurgitating behaviour of a larval cluster when it is disturbed.
- The processionary movement of the larval group as they move to a new feeding location on the tree.
Seasonal Indicators
- Larval infestations are most common and visible during autumn and winter in many parts of Australia.
- The emergence of adult sawflies is often synchronized and occurs in summer or autumn, sometimes triggered by rain.
Early Warning Signals
- Noticing the first small clusters of young larvae on leaves before they grow large enough to cause significant defoliation.
- Seeing adult females inspecting the leaves of a host plant is a sign that eggs may be being laid.
Prevention
Sanitation Measures
- There are few sanitation measures for sawflies. Raking up and disposing of leaf litter under a known host tree might remove some pupating individuals, but this is unlikely to be highly effective.
- Keeping trees healthy and well-watered can help them to withstand and recover from a defoliation event.
Exclusion Methods
- Exclusion is generally not practical for outdoor trees. For small, valuable plants, fine netting could be used during the adult egg-laying season to prevent females from accessing the foliage, but this is rarely done.
- Banding the trunks of trees with sticky barriers is not effective as the adults fly to lay their eggs on the leaves.
Landscaping Tips
- Promote biodiversity in your garden. A healthy garden with plenty of flowering plants will attract natural predators of sawfly larvae, such as predatory wasps, hoverflies, and birds.
- Avoid planting a monoculture of susceptible host plants (e.g., a fenceline of only one type of bottlebrush), as this can lead to more severe, concentrated infestations.
- When choosing trees, consider species that are less susceptible to sawfly attack in your local area.
Monitoring Strategies
- The most effective prevention is regular monitoring. Inspect susceptible plants (like eucalypts and bottlebrushes) from late summer through autumn for the first signs of egg-laying or small larval clusters.
- Early detection allows for control measures to be taken before the larvae grow large and the population explodes, preventing major defoliation.
- Check the undersides of leaves for the small slits where eggs may have been laid.
Environmental Modification
- Encourage natural predators. Birds like magpies, currawongs, and cuckoos are major predators of sawfly larvae. Creating a bird-friendly garden can provide excellent natural control. Parasitic wasps and flies also attack sawfly larvae and pupae, and their populations are supported by a diverse garden environment.
Control Methods
Professional Treatment Methods
Chemical Control
For large trees or severe infestations, a professional arborist can apply insecticides using high-pressure spraying equipment to reach the entire canopy. They may use contact insecticides or systemic products that are absorbed by the plant and kill the larvae as they feed. Systemic treatments can be more targeted and have less impact on other beneficial insects.
Biological Control
Professionals may use products based on natural pyrethrins or horticultural oils, which are effective and have a lower environmental impact than synthetic pyrethroids. In forestry, a specific nematode parasite has been successfully used as a biological control agent for the introduced Sirex Wood Wasp.
Physical Control
Not generally used by professionals, as it's not feasible on large trees.
Integrated Approach
An IPM strategy would involve correct identification, assessing the level of damage to determine if control is necessary, recommending methods to boost natural predators, and using the least toxic, most targeted chemical control option only when required.
DIY Treatment Options
Natural Remedies
The most effective natural remedy for small infestations is physical removal. A strong jet of water from a hose can dislodge the larval clusters from the branches. Once on the ground, they are vulnerable to predators like ants and birds. Alternatively, you can prune off the infested branch or leaves and dispose of them in a sealed bag or a bucket of soapy water.
Home Made Traps
Traps are not effective for sawflies.
Deterrent Methods
Spraying the foliage with horticultural oil or insecticidal soap can be effective. These products work by suffocating the soft-bodied larvae on contact and have a low impact on other wildlife. They must be applied thoroughly to cover the larval clusters.
Mechanical Control
For clusters within reach, you can physically remove them by hand (wearing gloves to avoid irritation from their secretions) and dropping them into soapy water.
Treatment Effectiveness
Success Rate
High for both professional and DIY methods if applied correctly and at the right time. Physical removal is very effective for small, accessible infestations.
Timeframe
Contact sprays and physical removal provide an immediate result. Systemic insecticides may take a few days to take effect.
Follow Up Required
Monitoring is required to ensure no clusters were missed. A follow-up spray may be needed a week or two later.
Seasonal Considerations
Treatment is most effective when the larvae are small and before they have caused extensive damage. It is pointless to spray after the larvae have left the tree to pupate in the soil.
Application Techniques
- Thorough coverage is essential when using contact sprays like horticultural oils or soaps.
- Systemic insecticides can be applied as a soil drench or a trunk injection by a qualified professional.
- Manual removal should be done by pruning the entire infested twig and disposing of it.
Professional Services
Professional Treatment Services
Chemical Control
For large trees or severe infestations, a professional arborist can apply insecticides using high-pressure spraying equipment to reach the entire canopy. They may use contact insecticides or systemic products that are absorbed by the plant and kill the larvae as they feed. Systemic treatments can be more targeted and have less impact on other beneficial insects.
Biological Control
Professionals may use products based on natural pyrethrins or horticultural oils, which are effective and have a lower environmental impact than synthetic pyrethroids. In forestry, a specific nematode parasite has been successfully used as a biological control agent for the introduced Sirex Wood Wasp.
Physical Control
Not generally used by professionals, as it's not feasible on large trees.
Integrated Approach
An IPM strategy would involve correct identification, assessing the level of damage to determine if control is necessary, recommending methods to boost natural predators, and using the least toxic, most targeted chemical control option only when required.
Professional Treatment Costs
For large ornamental trees, professional treatment by an arborist could cost $200-$500. In forestry, costs are part of larger pest management programs.
Treatment Success Rates
High for both professional and DIY methods if applied correctly and at the right time. Physical removal is very effective for small, accessible infestations.
Treatment Timeframe
Contact sprays and physical removal provide an immediate result. Systemic insecticides may take a few days to take effect.
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Browse All ProvidersSeasonal Patterns
Spring Activity
In spring, the larvae that have been feeding through winter are now fully grown. They descend from the trees to burrow into the soil and pupate. The tree may start to produce new growth to recover from the defoliation.
Summer Activity
This is often the time when adult sawflies emerge from their pupal cocoons in the soil, particularly after good rainfall. The winged adults mate, and the females search for suitable host plants to lay their eggs.
Autumn Activity
The eggs laid in summer hatch, and the young larvae begin to feed on the foliage. The larval clusters grow larger and more noticeable as autumn progresses. This is a key period for monitoring.
Winter Activity
The larval stage continues to feed and grow throughout the cooler winter months. This is when the most severe defoliation often occurs, as the large, late-instar larvae consume the most foliage.
Breeding Season
Adult mating and egg-laying typically occur in summer and early autumn.
Peak Activity Period
The peak of larval infestation and visible damage is usually through winter and into early spring.
Environmental Factors
Temperature Effects
Larval development may slow in very cold weather but continues through a typical temperate winter. Adult emergence is often triggered by warm temperatures.
Humidity Effects
Rainfall is a major trigger for the synchronized emergence of adult sawflies from the soil.
Photoperiod Effects
Day length likely plays a role in regulating the lifecycle, particularly the onset of pupation.
Weather Patterns
A wet summer can lead to a mass emergence of adults and a subsequent heavy larval infestation the following autumn and winter.
Legal Considerations
Pest Status
Native leaf-eating sawflies are generally considered an aesthetic or nuisance pest in gardens and a minor economic pest in some forestry settings. The introduced Sirex Wood Wasp is classified as a major economic and biosecurity pest.
Control Regulations
Standard regulations for pesticide use apply. For the Sirex Wood Wasp, specific interstate quarantine and control protocols may be in effect to limit its spread.
Professional Requirements
A pest management or arborist license is required for the commercial application of pesticides to control sawflies.
Environmental Considerations
As native sawflies are part of the ecosystem, control should be targeted and used only when necessary to prevent serious damage to valuable trees. Encouraging natural predators is the most environmentally sound approach. Broad-spectrum sprays should be avoided to protect pollinators and other beneficial insects.
Compliance Requirements
- Adherence to the product label is legally required for any pesticide application.
Frequently Asked Questions
Are 'spitfires' dangerous? Can they burn you?
The famous 'spitfire' grubs found on gum trees are the larvae of the Steel-blue Sawfly. Despite their intimidating name and defensive display, they are not dangerous to humans. The substance they regurgitate is not actually 'fire' or a chemical burn agent. It is a thick, sticky, non-acidic liquid made from the eucalyptus leaves they have eaten. While this substance can be irritating if it gets on your skin or in your eyes, causing a mild stinging sensation or rash in sensitive individuals, it is not a venom or a poison and will not cause a burn. The name 'spitfire' is purely descriptive of their defensive behaviour. It's best to avoid handling them to prevent irritation, but you don't need to fear being harmed by them.
I thought these were caterpillars. Why won't my caterpillar spray work?
This is a very common and important point of confusion. Sawfly larvae look remarkably like the caterpillars of moths and butterflies, but they belong to a completely different insect order (Hymenoptera, the wasp order) than caterpillars (Lepidoptera). This biological difference is critical when it comes to control. Many organic caterpillar sprays, particularly those containing *Bacillus thuringiensis* (Bt), work by targeting a specific protein that is unique to the digestive system of Lepidopteran caterpillars. Because sawfly larvae are not true caterpillars, their digestive systems are different, and they are completely immune to Bt-based insecticides. This is why correct identification is so important; using the wrong product will be completely ineffective and a waste of time and money.
Will sawfly larvae kill my gum tree?
In most cases, sawfly larvae will not kill a healthy, well-established eucalyptus tree. While a heavy infestation can be alarming and can completely strip the leaves from several branches or even a small tree, it is primarily an aesthetic issue. Healthy eucalypts are well-adapted to defoliation from native insects and will typically produce a new flush of growth in the following season once the larvae have moved on to pupate. However, repeated, severe defoliation year after year, or an attack on a tree that is already stressed by drought, disease, or poor soil conditions, can weaken the tree significantly and potentially contribute to its decline. For small, young, or valuable ornamental trees, it is often worth controlling a heavy infestation to reduce this stress.
What is the best way to get rid of sawfly larvae?
For small to medium-sized trees where the larval clusters are within reach, the best and most environmentally friendly method is physical removal. You can put on a pair of gloves and simply pick the entire cluster off the branch and drop them into a bucket of soapy water. Alternatively, you can prune off the infested twig or branch and dispose of it in a sealed bag. For clusters that are slightly out of reach, a strong jet of water from a hose can be very effective at dislodging them from the tree. Once on the ground, they are vulnerable to predators like ants and birds and are unlikely to make it back up the tree. For widespread infestations on large trees, chemical control with horticultural oils or soaps can be effective, but thorough coverage is needed. These methods are preferable to broad-spectrum insecticides which can harm beneficial insects.
What is an adult sawfly and does it sting?
The adult sawfly is the winged, reproductive stage of the insect. It looks similar to a stout-bodied wasp or bee, but it is completely harmless. A key feature is that it does not have the narrow 'wasp waist'. Adult sawflies **cannot sting**. The structure that looks like a stinger on the female is actually her ovipositor, which is shaped like a tiny saw. She uses this to cut slits into plant leaves to lay her eggs; she does not use it for defence and cannot penetrate human skin. The adults are often seen on flowers feeding on nectar, or flying around their host plants. They are short-lived and their only purposes are to mate and lay the eggs for the next generation of larvae. You do not need to be afraid of the adult sawfly.
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