Identification
Physical Characteristics
Size: Adult females are generally larger than males, with a body length ranging from 7mm to 12mm. Males are more slender and typically measure between 6mm and 10mm.
Coloration: The body colour is typically a uniform pale yellow-brown, cream, or light grey, sometimes with a greenish or pinkish tinge. The abdomen may be slightly darker than the cephalothorax. The legs are a similar pale colour. Critically, the fangs (chelicerae) and the area around them are a contrasting dark brown or black.
Key Features: Key features for identification are the pale, unmarked body, the dark chelicerae, the prominent spinnerets at the end of the abdomen, and their nocturnal, free-roaming hunting behaviour. The absence of a capture web and the presence of their silken sac-like retreats are also strong indicators.
Biology & Lifecycle
Development & Reproduction
Reproduction Rate: Females generally produce one or two egg sacs during their lifetime, usually in the warmer months. The parental investment is high, with the mother guarding the eggs until death.
Lifecycle Details
Egg Stage
After mating, the female Stout Sac Spider constructs a thick, white silk sac in a sheltered location, often within a curled leaf, under bark, or in a corner of a man-made structure. She lays a batch of 30 to 50 eggs inside this sac. Unusually for free-hunting spiders, the mother remains inside the sac, guarding her eggs fiercely until they hatch. She will not eat during this period and will defend the sac aggressively.
Larval Stage
Spiders do not have a distinct larval stage like insects.
Pupal Stage
Spiders do not undergo pupation. Their development is gradual.
Adult Stage
Spiderlings hatch within the safety of the egg sac and may even consume their mother (a behaviour known as matriphagy) for their first meal before dispersing. They grow by moulting periodically, each time constructing a new silk sac for the process. Their lifespan is typically around one to two years. They are active hunters throughout their life.
Reproduction Rate
Females generally produce one or two egg sacs during their lifetime, usually in the warmer months. The parental investment is high, with the mother guarding the eggs until death.
Generations Per Year
Typically one generation is produced per year. Spiderlings that hatch in late summer or autumn will overwinter as juveniles before maturing the following spring.
Development Time
The full development from egg to a sexually mature adult can take up to a year, depending heavily on factors like temperature and the availability of prey.
Seasonal Cycle
Activity peaks in the warmer months from spring through to autumn. This is when hunting, feeding, and mating occur. In winter, they become much less active and remain hidden in their retreats. Sightings indoors often increase in autumn as they seek sheltered places for overwintering or egg-laying.
Environmental Factors
The presence of ample insect prey and suitable locations for building their silk retreats (e.g., dense foliage, cluttered areas, cracks and crevices) are the primary factors supporting their populations.
Habitat & Distribution
Preferred Habitats
- In gardens, they live in foliage, under bark, in rockeries, and among leaf litter.
- They are commonly found in and around human dwellings, which offer abundant shelter and prey.
- Inside homes, they favour corners where walls meet the ceiling, curtain folds, and behind furniture.
- Sheds, garages, and woodpiles are also common habitats.
- They are adaptable and can be found in a wide range of terrestrial environments.
Distribution Patterns
Australian Distribution
Widespread in the more temperate and humid parts of Australia. It is commonly found in Queensland, New South Wales, the ACT, Victoria, Tasmania, and the southern parts of South Australia and Western Australia.
Climate Zones
- Subtropical
- Temperate
- Mediterranean
Urban vs Rural Distribution
Very common in both urban and rural environments. Suburban gardens and houses provide an ideal combination of shelter, prey, and suitable microclimates.
Native Range
Clubiona robusta is a species native to Australia.
Introduced Range
Not applicable.
Introduction History
Not applicable.
Current Spread
Their distribution is well-established and stable within the temperate and subtropical zones of the continent.
Limiting Factors
Their range is limited primarily by extreme aridity and potentially by regions with very cold, frosty winters.
Behavior & Diet
Activity Pattern
Strictly nocturnal. During the day, they rest inside a purpose-built silk sac. At night, they emerge to actively roam and hunt for prey. This is when they are most likely to be encountered by humans, often found climbing walls or ceilings indoors.
Dietary Preferences
Feeding Habits
They are generalist carnivores that actively hunt down their prey at night.
Health Risks
Always consult healthcare professionals for medical concerns related to pest exposure.
Disease Transmission
- There is no evidence that sac spiders transmit any diseases.
Allergens and Respiratory Issues
Allergic reactions to the venom are possible but appear to be rare. Symptoms would likely be limited to more extensive local swelling or itching.
Contamination Risk
Negligible. They do not infest food products.
Vulnerable Populations
- Individuals with a known sensitivity or allergy to insect or spider bites.
- Small children may experience more discomfort from the painful bite.
- Anyone can be bitten if the spider becomes trapped against the skin, for example, in clothing or bedding.
Symptoms of Exposure
- An immediate, sharp, burning pain at the bite site.
- Localised redness, swelling, and tenderness, which can last for several days.
- Itching and a persistent dull ache are common.
- In some cases, systemic symptoms like nausea, headache, and dizziness have been reported, but these are generally mild and transient.
- Blistering may occur at the bite site, but severe necrotic lesions are not a confirmed outcome of Clubiona bites in Australia. Proper wound care is important to prevent secondary infection.
Transmission Methods
- The only risk is from a defensive bite.
Risk Severity
Low to Moderate. The bite can be immediately painful and cause local symptoms, but it is not considered life-threatening. The main health concern has historically been the potential for necrotic ulcers, but modern clinical evidence has largely debunked this link for Australian sac spiders.
Economic Impact
Treatment Costs
Professional Treatment
$150-$400 for a general pest control treatment that would also manage sac spider populations by reducing their food source and applying barrier sprays.
Prevention Costs
$20-$60 annually for DIY barrier sprays and sealing gaps.
Diy Treatment
$20-$40 for a can of insecticide spray or dust for treating crevices.
Property Damage
Structural Damage
None.
Garden Damage
None. They are beneficial predators in the garden.
Food Contamination
None.
Equipment Damage
None.
Business Impact
Restaurant Issues
Their presence could be unsettling to patrons, but they are not a sanitation risk. Finding their sacs during cleaning would be the most likely issue.
Retail Impact
Minimal, though they could be found in stored goods.
Reputation Damage
A perceived 'spider problem' could cause minor reputational damage, especially in hospitality, due to public fear of spiders.
Operational Disruption
Minimal.
Agricultural Impact
Crop Damage
None.
Yield Loss
None.
Beneficial Aspects
In agricultural settings, they are considered beneficial predators, contributing to the natural control of various insect pests on foliage.
Economic Loss
They provide a net economic benefit in agriculture. The only potential cost is related to bites sustained by farm workers.
Indirect Costs
Healthcare Costs
Minimal. Most bites can be managed at home. A doctor's visit might be sought for pain relief or if secondary infection is suspected.
Cleanup Costs
Costs are limited to the time taken to vacuum away their silk sacs from corners.
Replacement Costs
None.
Detection & Signs
Visual Signs
- The most obvious and common sign is finding their white, silk sacs in the upper corners of rooms, window frames, or in the folds of curtains.
- Direct sightings of the pale, fast-moving spiders on walls or ceilings, particularly at night.
- Discovering a female guarding her egg sac, often in a more robust and thickly woven sac.
- Finding their small, shed skins (exuviae) near their silk retreats.
Physical Evidence
- The silk sacs are the primary physical evidence. These can be small and tubular for daytime resting, or larger and fluffier for egg-laying.
- Unlike other pests, they do not leave droppings, trails, or cause any physical damage.
Behavioral Signs
- Seeing them actively hunting at night is the main behavioural sign. They are agile climbers and move quickly.
- Their tendency to drop from the ceiling on a silk line when disturbed.
Seasonal Indicators
- An increase in sightings indoors during autumn as they seek shelter for overwintering and egg-laying.
- Activity is highest during the warmer months of spring and summer.
- Finding numerous tiny spiderlings in spring may indicate a nearby hatched egg sac.
Early Warning Signals
- Finding a single silk sac in a corner is the earliest warning sign that these spiders are present in your home.
- An increase in other household insects can predict that predators like sac spiders will soon follow.
Prevention
Sanitation Measures
- Reduce clutter in and around the home. Piles of boxes, paper, and clothing provide ideal hiding and retreat-building spots.
- Control other insect populations within the home to reduce the sac spider's food source. This includes regular cleaning, proper food storage, and dealing with other pests like flies and moths.
- Regularly vacuuming, paying special attention to corners where walls and ceilings meet, will remove spiders, their sacs, and their eggs.
Exclusion Methods
- Seal cracks and crevices in the building's exterior, including around windows, doors, and utility pipes, to block entry points.
- Install and maintain tight-fitting insect screens on all windows and doors.
- Use weather strips and door sweeps to seal gaps that allow entry.
- Be careful when bringing in items like firewood or pot plants from outside, as spiders can hitchhike on them.
Landscaping Tips
- Keep the perimeter of the house clear of dense vegetation, leaf litter, and woodpiles.
- Prune back trees and shrubs so they do not make contact with the house, removing a bridge for spiders to cross.
- Move rockeries and compost bins away from the house foundation.
- Avoid dense ground cover plants immediately adjacent to the building.
Monitoring Strategies
- Regularly inspect likely hiding spots, such as the corners of rooms, behind furniture, and inside closets and storage areas.
- The presence of their silk sacs is the easiest thing to monitor. A quick visual scan of a room's upper corners is an effective check.
- Sticky traps placed along skirting boards can sometimes catch these wandering hunters, indicating their presence.
Environmental Modification
- Using yellow 'bug lights' for exterior lighting can attract fewer of the insects that sac spiders prey on, making the immediate vicinity of your home less attractive to them.
Control Methods
Professional Treatment Methods
Chemical Control
A professional pest controller can apply a residual insecticide barrier spray to the exterior of the home, as well as treat key internal areas like skirting boards, roof voids, and crevices. Insecticidal dusts may also be used in wall cavities and voids.
Biological Control
Not a viable option for this species in a domestic setting.
Physical Control
A thorough professional service will include the physical removal of existing spiders and their silk sacs using a vacuum cleaner.
Integrated Approach
The best professional approach is an IPM strategy, combining chemical barriers with physical removal, exclusion advice (sealing gaps), and recommendations for habitat modification (reducing clutter and vegetation).
DIY Treatment Options
Natural Remedies
Regular vacuuming is the most effective natural remedy. Some people use peppermint oil or eucalyptus oil as a repellent, though their effectiveness is not scientifically proven.
Home Made Traps
Sticky traps placed in corners and along walls can be effective at catching individual wandering spiders.
Deterrent Methods
Maintaining a clean, clutter-free environment and sealing entry points are the most effective deterrents.
Mechanical Control
Vacuuming up spiders and their sacs is the primary DIY mechanical control method. A direct spray with a household insecticide will also kill individual spiders on contact.
Treatment Effectiveness
Success Rate
Professional treatments are generally highly effective, providing control for several months. DIY methods require more persistence.
Timeframe
A professional spray will have an immediate knockdown effect and provide a protective barrier. Population reduction will be noticeable within a few days.
Follow Up Required
Annual general pest treatments are often recommended to maintain control, especially in areas with high spider pressure.
Seasonal Considerations
Treatment is most effective when applied in spring or autumn to target them as they become active or seek shelter.
Application Techniques
- Perimeter spraying of the building's exterior foundation and entry points.
- Targeted application of insecticide dust to roof voids and wall cavities.
- Crack and crevice treatment internally and externally.
- Physical removal of sacs and webs using a vacuum cleaner.
Professional Services
Professional Treatment Services
Chemical Control
A professional pest controller can apply a residual insecticide barrier spray to the exterior of the home, as well as treat key internal areas like skirting boards, roof voids, and crevices. Insecticidal dusts may also be used in wall cavities and voids.
Biological Control
Not a viable option for this species in a domestic setting.
Physical Control
A thorough professional service will include the physical removal of existing spiders and their silk sacs using a vacuum cleaner.
Integrated Approach
The best professional approach is an IPM strategy, combining chemical barriers with physical removal, exclusion advice (sealing gaps), and recommendations for habitat modification (reducing clutter and vegetation).
Professional Treatment Costs
$150-$400 for a general pest control treatment that would also manage sac spider populations by reducing their food source and applying barrier sprays.
Treatment Success Rates
Professional treatments are generally highly effective, providing control for several months. DIY methods require more persistence.
Treatment Timeframe
A professional spray will have an immediate knockdown effect and provide a protective barrier. Population reduction will be noticeable within a few days.
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Browse All ProvidersSeasonal Patterns
Spring Activity
Spiders that overwintered as juveniles reach maturity. Young spiders disperse from egg sacs. Activity and feeding increase as temperatures rise.
Summer Activity
This is the peak active season for hunting and growth. Mating occurs during this period.
Autumn Activity
A second peak in activity is often noticed as spiders, including gravid females, actively seek sheltered sites to overwinter or lay eggs. This is when they are most commonly found indoors.
Winter Activity
Spiders become inactive, remaining hidden inside their insulated silk sacs to wait out the cold. They do not hunt and sightings are rare.
Breeding Season
Breeding can occur from late spring through summer.
Peak Activity Period
Indoor encounters and the presence of sacs are most commonly reported in autumn (March-May).
Environmental Factors
Temperature Effects
Warm temperatures drive activity, while cold induces a state of torpor.
Humidity Effects
They seem to prefer moderately humid conditions found in temperate coastal regions.
Photoperiod Effects
Their nocturnal hunting cycle is cued by the onset of darkness.
Weather Patterns
They are more likely to be driven indoors by heavy rain or the onset of cold weather fronts.
Legal Considerations
Pest Status
Considered a minor or domestic pest, primarily due to its tendency to enter homes and its (often exaggerated) reputation for venomous bites.
Control Regulations
Standard regulations for the application of pesticides by licensed professionals apply. There are no specific regulations targeting this species.
Professional Requirements
A pest management license is required for any commercial application of pesticides to control these spiders.
Environmental Considerations
They are native predators that play a role in controlling insect populations. Broad-spectrum outdoor spraying should be done cautiously to avoid harming non-target beneficial species. Targeted treatments are preferred.
Compliance Requirements
- Adherence to the chemical label's instructions is legally required.
- Safety protocols must be followed to protect residents and pets.
Frequently Asked Questions
Is the Stout Sac Spider bite dangerous and does it cause flesh to rot?
This is a very common question due to historical reports. While the bite of a Stout Sac Spider (*Clubiona robusta*) can be quite painful and medically significant, the link to severe, flesh-rotting ulcers (necrotic arachnidism) is now largely considered unproven and likely incorrect for Australian species. Decades of clinical evidence and research have failed to definitively establish sac spiders as the cause of such lesions. A typical bite will result in immediate sharp pain, followed by local redness, swelling, and tenderness that can last for several days. Some people may experience mild systemic symptoms like nausea or headache. The main danger is not necrosis, but a potential secondary bacterial infection if the bite wound is not kept clean. So, while you should treat the spider with respect as its bite is unpleasant, the fear of it causing flesh to rot is not supported by modern science.
What are the white sacs I'm finding in the corners of my rooms?
If you are finding thick, white, silken sacs, particularly in the upper corners where walls meet the ceiling, it is highly likely you have sac spiders. These are not webs for catching prey, but are retreats the spiders build for themselves. They serve several purposes. The spider will rest inside the sac during the day to stay hidden and protected. It will also construct a sac to safely shed its skin as it grows (moulting). Most importantly, a female will build a very robust sac to lay her eggs in, and she will remain inside to guard them. Finding these sacs is the number one sign of a sac spider presence in your home. They can be easily removed with a vacuum cleaner during regular cleaning to help manage the population.
Why are sac spiders coming into my house?
Sac spiders come indoors for the same reasons as many other spiders: food and shelter. Your home provides a stable, climate-controlled environment with plenty of hiding places, such as cracks, crevices, and corners. It also often harbours a supply of the sac spider's prey, such as small insects and other spiders. They are active nocturnal hunters, and in their nightly wanderings, they can easily slip inside through small gaps under doors or around windows. They are particularly prone to moving indoors in autumn. At this time, the weather is cooling, and they are actively looking for warm, protected sites to build their sacs for overwintering or for laying their eggs. Reducing clutter and sealing entry points are the best ways to discourage them from choosing your house as their home.
How can I get rid of sac spiders without using chemicals?
You can effectively manage sac spiders without resorting to chemical sprays. The most important tool is your vacuum cleaner. Regularly vacuum all corners of rooms, especially where the walls meet the ceiling, behind furniture, and inside closets. This will physically remove the adult spiders, their protective sacs, and any eggs they contain. Secondly, focus on exclusion by sealing any cracks or gaps in your home's exterior. Install weather stripping on doors and repair any damaged fly screens. Thirdly, reduce their food source by keeping your home clean and dealing with any other insect pests. Finally, reduce clutter like piles of boxes or papers, as these provide perfect hiding spots. These physical and environmental control methods are highly effective and are the preferred approach for this species.
Are Stout Sac Spiders aggressive?
Stout Sac Spiders are not considered aggressive in that they do not seek out humans to attack. However, they are known to be defensive and are more prone to biting than many other common household spiders. They will not hesitate to bite if they feel threatened or trapped. Most bites occur accidentally when a spider is inside clothing, bedding, or a shoe and gets pressed against a person's skin. In its panic, it bites in self-defence. When discovered in the open, their first instinct is to flee with great speed. So, while you don't need to fear an unprovoked attack, you should exercise caution and avoid handling them or trapping them in a way that might provoke a defensive reaction.
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