Identification
Physical Characteristics
Size: Females are robust and can have a body length of up to 30mm. Males are smaller and more slender, typically around 15-18mm in length.
Coloration: The cephalothorax and legs are typically dark brown to shiny black. The abdomen is where the key feature lies: the posterior end is abruptly truncated and forms a hardened, disc-like 'shield' that is usually dark and leathery, with deep grooves and bristles.
Key Features: The primary, unmistakable distinguishing feature is the hardened, shield-like abdomen used for phragmotic defence (plugging the burrow). The fan of twigs radiating from the burrow entrance is also a unique behavioural identifier.
Biology & Lifecycle
Development & Reproduction
Reproduction Rate: Reproduction is a slow process. A female might only reproduce every few years, investing significant time and energy into a single clutch of offspring.
Lifecycle Details
Egg Stage
After mating, the female lays her eggs within a silk sac which she secures deep inside her burrow. This subterranean chamber provides a stable, protected environment with controlled temperature and humidity, shielding the eggs from predators and the harsh external climate.
Larval Stage
Upon hatching, the spiderlings remain within the mother's burrow for an extended period, sometimes for up to nine months. They subsist on yolk and may share food captured by the mother, benefiting from her protection during their most vulnerable stage.
Pupal Stage
Spiders undergo incomplete metamorphosis and do not have a pupal stage. They grow by shedding their exoskeleton periodically.
Adult Stage
This species is exceptionally long-lived. Females are estimated to live for 15-20 years or even longer, a testament to the effectiveness of their burrow-dwelling, defensive lifestyle. They may never travel more than a few meters from where they were born. Males mature more quickly, in about 3-5 years, and have a short adult life of a few months dedicated to reproduction, after which they perish.
Reproduction Rate
Reproduction is a slow process. A female might only reproduce every few years, investing significant time and energy into a single clutch of offspring.
Generations Per Year
Far less than one generation per year. The population is a mix of many overlapping generations, making them very slow to recover from disturbances.
Development Time
The development from spiderling to a sexually mature adult is a multi-year process, taking approximately 3-5 years for males and 5-7 years for females.
Seasonal Cycle
Females are active within their territory year-round but hunt mostly at night during milder weather. The key seasonal event is the wandering of males during the autumn and winter months (typically May to July), often triggered by rainfall, when they search for female burrows.
Environmental Factors
The presence of suitable loamy or clay soils for stable burrow construction is paramount. Their distribution is tightly linked to these soil types within their climatic range. Habitat fragmentation due to agriculture is a major threat.
Habitat & Distribution
Preferred Habitats
- Native woodlands, mallee, and heathlands of the Western Australian wheatbelt.
- Specific patches of loamy or clay-rich soils that are firm enough to support a permanent burrow.
- Areas with a good supply of leaf litter and twigs for use in burrow camouflage and trip-lines.
- Unfortunately, their prime habitat has been heavily cleared for agriculture.
- They are less common in suburban gardens compared to some other trapdoor species.
Distribution Patterns
Australian Distribution
Found only in Western Australia.
Climate Zones
- Temperate
- Mediterranean
- Semi-Arid
Urban vs Rural Distribution
Primarily a rural species found in remnant patches of native bushland. They are not typically found in urbanized environments, which usually lack the specific soil and habitat requirements.
Native Range
Endemic to the south-west of Western Australia.
Introduced Range
Not introduced elsewhere.
Introduction History
A native species with a long evolutionary history in WA.
Current Spread
The species is not spreading. In fact, its range is contracting and becoming increasingly fragmented due to widespread land clearing for agriculture in the WA wheatbelt.
Limiting Factors
Habitat loss and fragmentation are the primary limiting factors. Unsuitable soil types and complete lack of vegetation cover also prevent their establishment.
Behavior & Diet
Activity Pattern
Strictly nocturnal. Females hunt from the entrance of their burrows at night. Males wander nocturnally during the autumn/winter mating season.
Dietary Preferences
Feeding Habits
Generalist carnivore, preying on ground-dwelling invertebrates.
Health Risks
Always consult healthcare professionals for medical concerns related to pest exposure.
Disease Transmission
- There is no evidence or theoretical risk of disease transmission from these spiders to humans.
- They are not known to be vectors for any human pathogens.
- Their clean, subterranean lifestyle isolates them from disease agents.
- No known bacterial, viral, or parasitic risks.
- They pose no threat of contamination.
Allergens and Respiratory Issues
Allergic reactions to the venom are theoretically possible but unrecorded and likely to be extremely rare.
Contamination Risk
Zero risk of food or surface contamination.
Vulnerable Populations
- Small children, who should be taught not to disturb wildlife.
- Agricultural workers and researchers working in their specific habitat are the most likely to encounter them.
- Pets that dig or harass the spider's burrow might provoke a defensive bite.
- People involved in land clearing or construction in their habitat.
- Due to their rarity and non-aggressive nature, encounters are very infrequent.
Symptoms of Exposure
- Sharp, mechanical pain from the bite itself.
- Potential for localized swelling and redness around the bite site.
- Systemic symptoms like nausea are not expected.
- Any symptoms should resolve within a day or two.
- Medical advice should be sought mainly to confirm the spider's identity and to clean the wound to prevent secondary infection.
Transmission Methods
- The only potential health impact is from a direct defensive bite, which is a highly unlikely event.
- Contact would require unearthing the spider or cornering a wandering male.
- No other transmission pathways exist.
- Food contamination is impossible.
- They are not a disease vector.
Risk Severity
The overall health risk is Low. A bite would be painful from the large fangs, but the venom is not considered dangerous to humans. The spider is non-aggressive and will always choose to hide over biting.
Economic Impact
Treatment Costs
Professional Treatment
$200-$400 for a pest controller to address home incursions by wandering males, primarily through sealing entry points. Relocation, not destruction, should be requested if a burrow is unearthed.
Prevention Costs
$30-$80 for weather seals and gap fillers to exclude wandering males from homes.
Diy Treatment
$10-$30 for a container to safely relocate a spider found indoors.
Property Damage
Structural Damage
Causes no damage to structures.
Garden Damage
Causes no damage to gardens. Their presence is an indicator of healthy, undisturbed soil.
Food Contamination
No risk.
Equipment Damage
No risk.
Business Impact
Restaurant Issues
None.
Retail Impact
None.
Reputation Damage
None.
Operational Disruption
May cause minor disruptions to construction or agricultural projects if found in an area where they are protected, potentially requiring ecological assessment and relocation efforts.
Agricultural Impact
Crop Damage
None. Their habitat is native vegetation, not cropland.
Yield Loss
None.
Beneficial Aspects
They are important predators in their native ecosystem and indicators of ecosystem health. Their long-term presence signifies stable, undisturbed habitat.
Economic Loss
No direct economic loss. The main 'impact' is the cost associated with conservation efforts and potential delays to development projects in sensitive habitats.
Indirect Costs
Healthcare Costs
Effectively zero due to the rarity of bites.
Cleanup Costs
None.
Replacement Costs
None.
Preventive Maintenance
Costs are associated with excluding wandering males from rural homes or with conservation management on properties that contain their habitat.
Detection & Signs
Visual Signs
- The term 'infestation' is inappropriate given their conservation status. Signs of 'presence' are key.
- The most definitive sign is the burrow entrance with its fan of radiating twigs.
- Finding a wandering male inside a rural property during the autumn/winter wet season.
- The discovery of a burrow during digging or excavation, often with the spider plugging the entrance.
- The hardened, disc-like shield of the spider is sometimes visible as it plugs the burrow flush with the soil surface.
Physical Evidence
- The twig-lined burrow itself is the main evidence.
- A dead male spider found indoors or in a pool filter on a rural WA property.
- The discovery of a deep, silk-lined vertical shaft in the ground when digging.
- Insect remains scattered among the twig-lines near the burrow entrance.
- Finding an unearthed female during land clearing is a clear sign of a local population.
Behavioral Signs
- The spider retreating and plugging its burrow when disturbed.
- Observing a spider at night sitting at the entrance, 'listening' to its trip-lines.
- A wandering male walking across a path or patio at night in autumn/winter.
- An aggressive threat posture if the spider is removed from its burrow and cornered.
- Their completely sedentary nature means you will not see them actively moving around the garden, only at the burrow entrance.
Seasonal Indicators
- Male wandering is strictly seasonal, occurring in the wet autumn and winter months (May-July).
- Burrows are present year-round but may be more visible after rain when the soil is dark.
- Increased likelihood of unearthing them during earthworks in the drier summer months.
- Breeding and egg-laying occurs within the burrow after the winter mating season.
Early Warning Signals
- Finding a single twig-lined burrow is an 'early warning' that a protected and significant species is present.
- Finding a wandering male indoors indicates a local population exists nearby.
- For developers, finding one burrow should trigger a more thorough ecological survey of the area.
Prevention
Sanitation Measures
- Sanitation is not relevant to preventing this species.
- Clearing native vegetation is actively harmful to them and is not a 'prevention' method.
- Around rural homes, keeping a clear, non-vegetated perimeter can deter wandering males from approaching the house itself.
- Do not remove twigs and leaf litter from remnant bushland on your property, as this is their habitat and building material.
Exclusion Methods
- For rural properties within their habitat range, exclusion is the key to preventing home entry by wandering males.
- Install high-quality weather seals and door sweeps on all external doors.
- Seal all cracks, crevices, and utility entry points in the building's foundation and walls.
- Ensure insect screens are well-maintained and that weep holes are fitted with mesh guards.
- This is the most responsible and effective form of 'control'.
Landscaping Tips
- The primary landscaping tip is conservation. If you have remnant bushland on your property, preserve it.
- Avoid large-scale soil disturbance in areas where they might live.
- If you find a burrow, the best practice is to mark its location and avoid the area. Do not 'tidy up' the twig-lines.
- Creating a buffer zone of lawn or gravel between native bushland and your house can reduce the chances of wandering males reaching your door.
- Do not attempt to move soil from an area with burrows to another area, as this will destroy the burrows and kill the spiders.
Monitoring Strategies
- If you know they are on your property, monitor the area by looking for new burrows (a sign of juvenile dispersal).
- During autumn/winter, be vigilant for wandering males around the house at night.
- Check and maintain your exclusion seals and barriers before the wandering season begins.
- For conservation purposes, some landholders engage in population monitoring with local naturalist groups or government agencies.
Environmental Modification
- Environmental modification should be focused on conservation, not elimination.
- Re-establishing native vegetation corridors can help connect fragmented populations.
- Avoid changing drainage patterns in a way that would flood or dry out known habitat areas.
- Any modification should be to protect and enhance their habitat, not remove it.
Control Methods
Professional Treatment Methods
Chemical Control
Absolutely not recommended or appropriate. This species is of conservation concern. Using pesticides is environmentally irresponsible and could have legal implications if the local population is protected. Pest controllers should refuse to apply chemicals for this species.
Biological Control
None exist or are needed.
Physical Control
If a wandering male is inside, a pest controller should use the 'container and card' method to remove and release it. If a female's burrow must be moved for construction, an ecologist or specialist should be called to carefully excavate and translocate the entire burrow contents.
Integrated Approach
The only acceptable IPM approach is: 1. Identification. 2. Assessment of conservation status. 3. Implementing exclusion methods for buildings. 4. If a spider must be moved, professional and careful relocation is the only option.
DIY Treatment Options
Natural Remedies
None are applicable. The goal should be co-existence or exclusion from buildings.
Home Made Traps
Trapping is discouraged as it could harm a protected species.
Deterrent Methods
The only effective deterrent is physical exclusion from buildings.
Mechanical Control
The 'container and card' method is the correct DIY approach for a wandering male found indoors. Safely capture it and release it back into a suitable habitat area on your property, away from the house.
Treatment Effectiveness
Success Rate
Exclusion methods have a 100% success rate for preventing indoor entry when properly installed and maintained.
Timeframe
Exclusion provides an immediate and permanent solution.
Follow Up Required
Annual checks of seals and barriers are all that is required.
Seasonal Considerations
Ensure exclusion measures are in place before the autumn/winter wandering season.
Application Techniques
- Relocation: Use a container and card for males. For females, careful excavation of the entire burrow by a specialist is required.
- Exclusion: Meticulous sealing of all potential entry points into a building.
- Marking and Avoidance: If a burrow is found, mark the location and avoid disturbing it.
- Safety protocols: When relocating a male, wear gloves for peace of mind, though they are not aggressive.
Professional Services
Professional Treatment Services
Chemical Control
Absolutely not recommended or appropriate. This species is of conservation concern. Using pesticides is environmentally irresponsible and could have legal implications if the local population is protected. Pest controllers should refuse to apply chemicals for this species.
Biological Control
None exist or are needed.
Physical Control
If a wandering male is inside, a pest controller should use the 'container and card' method to remove and release it. If a female's burrow must be moved for construction, an ecologist or specialist should be called to carefully excavate and translocate the entire burrow contents.
Integrated Approach
The only acceptable IPM approach is: 1. Identification. 2. Assessment of conservation status. 3. Implementing exclusion methods for buildings. 4. If a spider must be moved, professional and careful relocation is the only option.
Professional Treatment Costs
$200-$400 for a pest controller to address home incursions by wandering males, primarily through sealing entry points. Relocation, not destruction, should be requested if a burrow is unearthed.
Treatment Success Rates
Exclusion methods have a 100% success rate for preventing indoor entry when properly installed and maintained.
Treatment Timeframe
Exclusion provides an immediate and permanent solution.
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Browse All ProvidersSeasonal Patterns
Spring Activity
Very low observable activity. Juveniles may be dispersing from maternal burrows.
Summer Activity
Spiders remain sealed deep in their burrows to escape the extreme heat and dry conditions of the WA summer.
Autumn Activity
A key activity period. As temperatures cool and rains begin, males emerge from their burrows at night to search for mates. This is when they may enter homes.
Winter Activity
Male wandering continues into the wet winter months. This is the peak mating season.
Breeding Season
The main breeding season is autumn and winter.
Peak Activity Period
The peak period for human-spider encounters (wandering males indoors) is from May to July.
Environmental Factors
Temperature Effects
Activity is driven by the cooler, mild temperatures of autumn and winter.
Humidity Effects
Rainfall is the primary trigger for male wandering.
Photoperiod Effects
Shorter day lengths of autumn signal the start of the mating season.
Weather Patterns
The first major rains of autumn will often trigger a synchronized emergence of wandering males.
Legal Considerations
Pest Status
This species has no pest status. It is often a species of significant conservation concern, and some populations may be formally protected under state or federal environmental law.
Control Regulations
There are no regulations for 'control', but there can be significant legal penalties for harming a protected species or its habitat. It is illegal to knowingly kill or disturb them in protected areas.
Professional Requirements
A pest controller operating in their habitat should have ecological awareness and prioritize identification and conservation. For translocation, an ecologist may be legally required.
Environmental Considerations
The primary consideration is the protection of this species and its dwindling habitat. All actions should be viewed through a conservation lens.
Compliance Requirements
- Compliance with the Western Australian Biodiversity Conservation Act 2016 if the species is listed.
- Developers may be required to conduct ecological surveys and implement management plans.
- Any relocation efforts may require specific permits.
- Homeowners on properties with this species should contact the WA Department of Biodiversity, Conservation and Attractions for advice.
- Killing them is unethical and potentially illegal.
Frequently Asked Questions
What is the 'shield' on a Shieldbacked Trapdoor Spider for?
The 'shield' is a remarkable evolutionary adaptation for defence, a behaviour known as phragmosis. The rear end of the spider's abdomen is not rounded like in most spiders; instead, it's abruptly cut off, hardened, and grooved, forming a tough disc. When the spider is threatened, typically by a predator like a spider-hunting wasp trying to enter its burrow, it retreats inside and positions its abdomen at the entrance. The shield fits the burrow opening perfectly, acting like a living manhole cover. This hardened plug is incredibly difficult for a predator to bite, grip, or sting. It allows the spider to effectively seal itself inside its fortress, providing a highly effective defence against its natural enemies. This unique feature is the most defining characteristic of the species and is a brilliant example of specialized evolution for a subterranean lifestyle.
I found a burrow with twigs around it. Is it a Shieldbacked Spider and is it dangerous?
If you are in Western Australia and you've found a ground burrow with a fan of twigs, leaves, or silk lines radiating from the entrance, it is almost certainly the home of a Shieldbacked Trapdoor Spider (*Idiosoma nigrum*) or a very close relative. This twig-lining behaviour is unique to them and serves as an extended sensory system to detect passing prey. In terms of danger, they are not considered medically significant to humans. They are extremely shy, non-aggressive spiders. Their first, second, and third instinct is to hide in their burrow and plug the entrance. A bite would only be possible if you were to dig one up and physically restrain it. Even then, while the bite would be painful due to their size, the venom is not dangerous. The spider poses virtually no risk to people or pets, and its presence is a sign of a healthy, intact native ecosystem.
I think I have Shieldbacked Spiders on my property. Should I call a pest controller?
Calling a pest controller with the intention of extermination is the wrong approach for this species and should be avoided. These spiders are of conservation concern, and their populations are threatened by habitat loss. A responsible pest controller should refuse to use pesticides on them. If you are concerned about wandering males entering your home during the autumn/winter mating season, a pest controller can be helpful in a different way: they can inspect your home and help you identify and seal potential entry points (a service called 'pest-proofing' or 'exclusion'). If you have unearthed a female's burrow during construction or landscaping and are concerned for its welfare, the correct course of action is to contact the Western Australian Museum or the Department of Biodiversity, Conservation and Attractions for advice. They may be able to connect you with a specialist who can safely translocate the spider.
Why is the Shieldbacked Trapdoor Spider considered a species of conservation concern?
The Shieldbacked Trapdoor Spider's conservation status is precarious due to a combination of its biology and human activity. Its prime habitat is the native woodlands and heathlands of the Western Australian wheatbelt, an area that has been subjected to massive-scale land clearing for agriculture over the last century. This has resulted in severe habitat loss and fragmentation. Because these spiders have very poor powers of dispersal—the young simply walk a few meters from their mother's burrow—they cannot cross cleared land like paddocks or roads to colonize new areas. This means that remnant populations in small patches of bushland become isolated and are highly vulnerable to local extinction from threats like fire, chemical drift, or further clearing. Their incredibly slow growth and long lifespan also mean that populations recover very slowly, if at all. They are a classic example of a species whose specialized, sedentary lifestyle makes it unable to cope with rapid, large-scale changes to its environment.
How should I act if I find a Shieldbacked Trapdoor Spider?
The best course of action is one of minimal disturbance and appreciation. If you find a wandering male inside your home, use the 'container and card' method to safely capture it and release it outside in a vegetated or mulch-covered area away from your house. If you discover a burrow in your garden or on your property, the best thing to do is to leave it alone. Mark its location so you don't accidentally dig it up. Avoid 'tidying up' the area by removing the twigs around the entrance, as these are vital for the spider's survival. Consider yourself fortunate to be a custodian of such a unique and ancient creature. If you are in a position to do so, taking a clear photograph of the burrow or the spider and submitting it with location details to the WA Museum's reporting app (such as ClimateWatch or Faunabase) can provide valuable data for scientists working to understand and protect the species.
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Image Gallery
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