Fishing Spider
Dolomedes spp.
In commercial settings near water — marinas, waterfront facilities, food-processing plants near waterways, and buildings with surface water management ponds — fishing spiders may occasionally be encountered at ground level or in damp lower-level areas.
They are entirely non-aggressive, rarely enter dry interior spaces, and present no food safety or health risk.
Their large size and sudden appearance near water features may surprise staff or customers, but no chemical intervention is warranted. Fishing spiders are a natural component of healthy aquatic ecosystems and their presence often indicates good water quality nearby.
Habitat
Commercially, fishing spiders inhabit areas near surface water — drainage ditches, retention ponds, loading areas with standing water, and waterfront properties.
They may enter lower-level spaces of buildings adjacent to poorly drained ground.
Facilities near the Thames River, Lake Erie shoreline, or agricultural drainage canals in the Windsor-Essex region should expect occasional exterior encounters. Indoor presence is limited to wet or damp utility areas and is not indicative of a structural infestation.
Active Areas
Windsor
Occasional sightings near the Detroit River waterfront and in properties with garden water features; not commonly encountered inland.
Tecumseh
Infrequent; encountered near Lake St. Clair shoreline margins and adjacent drainage areas.
LaSalle
Sporadic sightings near the Detroit River corridor and low-lying properties; not a common residential concern.
Amherstburg
Present near the Detroit River and shoreline; properties bordering the river may encounter adults in late summer.
Lakeshore
The highest encounter rate in the region due to extensive Lake St. Clair shoreline, drainage channels, and marshy margins providing ideal habitat.
Essex
Encountered near agricultural drainage ditches and water management channels; not a common concern in residential areas.
Kingsville
Occasional sightings near Lake Erie shoreline and marsh areas; greenhouse irrigation ponds may also support populations.
Leamington
Present near Point Pelee shoreline and Rondeau Bay margins; encountered by homeowners near the lakeshore.
Chatham-Kent
Moderate prevalence near the Thames River, Lake Erie shoreline, and other waterways in Chatham-Kent. Not typically a structural pest.
St. Thomas
Low prevalence. Occasional finds near Kettle Creek and adjacent properties.
Seasonality
Commercial encounters follow the same seasonal pattern. The highest frequency of building entry incidents occurs in late spring and again in September to October as adults seek sheltered overwintering sites near structures.
Facilities with permanent water features on-site should anticipate spider activity from May through October and plan any aesthetic or exclusion management accordingly.
Spring
Summer
Autumn
Winter
Appearance
In commercial environments, fishing spiders are identified by the same features — large size, pale lateral stripe, and flattened resting posture.
Workers encountering one in a basement or near a floor drain will be confronted with a spider considerably larger than any typical house spider.
Unlike wolf spiders, fishing spiders have a distinctly flattened profile and are associated with moisture; finding one in a dry storage room or on an upper floor would be unusual and likely indicates the individual has wandered far from its preferred habitat.
- Large, flattened body with legs spread wide — female body length 15–26 mm, with leg span reaching 60–75 mm
- Distinctive pale cream or white stripe running along each side of the body and cephalothorax
- Capable of walking on the water surface using surface tension, and diving underwater to escape predators or catch aquatic prey
- Found near water features, ponds, streams, marshy edges, and damp basement areas
- Does not construct a web for prey capture — hunts actively with legs resting on the water surface to detect vibrations
- Alarming due to large size but not medically significant — considered one of the largest spiders found in Ontario
Behaviour
In commercial settings, fishing spiders behave as they do in natural habitats — largely passive, non-aggressive, and reactive. They do not seek out human activity and will retreat when disturbed.
Their nocturnal and crepuscular activity means encounters in commercial premises with regular human traffic are infrequent. A fishing spider found indoors is almost always a wandering individual that entered accidentally and does not represent an established interior population.
Lifecycle
Egg
Egg sacs carried by female fishing spiders near commercial water features or drainage areas are rarely noticed.
If one is observed near a building entry point, the female will move away when approached and does not pose a threat. The sac and female should not be disturbed or destroyed, as this species is a non-target beneficial predator.
Spiderling
Juvenile fishing spiders disperse from nursery webs in waterside vegetation and are effectively invisible at commercial scale.
They do not enter buildings and present no operational concern. Their development through autumn means a new cohort of adults will be present near water features the following spring.
Adult
Adult fishing spiders are the stage most relevant to commercial facilities near water. They are encountered on exterior building walls adjacent to water, around perimeter drainage, and occasionally in wet utility rooms or pump rooms.
A single adult sighting does not warrant pesticide application. Facilities should document sightings and ensure ground-level gaps near water are sealed to prevent further entry.
Signs You May Have a Problem
- Large, flat-bodied spiders with pale lateral stripes observed near building perimeter drainage channels, retention ponds, or waterfront areas
- Sightings in wet utility rooms, pump rooms, or basement areas with floor drains adjacent to exterior surface water
- A large spider seen walking on the surface of an on-site water feature or drainage pond
- Female carrying a prominent spherical egg sac observed near ground-level entry points adjacent to water
- Staff reports of very large spiders in lower-level utility or maintenance areas following heavy rainfall
- Sticky traps placed in wet utility rooms capturing large-bodied, long-legged spiders with pale lateral banding
Risks & Concerns
In commercial environments, fishing spiders carry no meaningful health or food-safety risk. Their non-aggressive disposition makes bites in the workplace effectively non-existent under normal conditions.
The primary concern is the psychological impact of large spider sightings on staff and customers.
For regulated food-handling facilities, documentation of the sighting and any exclusion measures taken may be required for audit records, but no specific regulatory treatment threshold applies to this species.
Prevention
- Seal ground-level gaps, expansion joints, and utility penetrations on exterior walls adjacent to drainage channels, retention ponds, or waterside areas.
- Maintain functional door sweeps on all ground-level access doors, particularly in wet utility and pump room areas.
- Improve drainage around the building perimeter to eliminate persistently wet soil that creates preferred habitat.
- Ensure basement and utility room window screens are intact and properly fitted.
- Brief staff on identification so that fishing spider sightings are not misidentified as dangerous species requiring emergency treatment.
DIY Control
- Exclusion caulking and door sweep installation on ground-level access points adjacent to water are the most effective DIY-level intervention.
- Staff physical relocation of individual spiders using a container and card is appropriate and does not require chemical application.
- Sticky monitoring traps in wet utility rooms confirm whether a sighting is an isolated wanderer or part of ongoing ingress.
Professional Control
- If fishing spiders are repeatedly entering a commercial facility, a licensed pest control technician should conduct a thorough exterior audit to identify and seal all ground-level entry points near water.
- Residual perimeter insecticide treatment at foundation level can reduce incidental entry if exclusion alone is insufficient.
- IPM consultants should note this species in their reports as non-target beneficial wildlife and recommend exclusion as the primary strategy, with chemical treatment only as a secondary measure.