Are black widow spiders common in Montreal?

The Northern Black Widow (Latrodectus variolus) is present in Quebec but not common in urban Montreal. They are more frequently found in suburban and rural areas with woodpiles, rock piles, and outbuildings. Sightings in Montreal proper are relatively rare but do occur, particularly in properties with gardens, decks, and firewood storage.

What should I do if I think I was bitten by a black widow?

Go to the emergency room immediately — do not wait for symptoms to develop. Bring the spider if you can safely capture it (in a sealed container) for identification. Antivenom is available and highly effective when administered promptly. Symptoms of latrodectism (severe muscle cramps, sweating, nausea) typically develop 30–60 minutes after the bite.

How do I tell a black widow from other black spiders?

The key identifier is the red or orange hourglass marking on the underside of the female's round, glossy black abdomen. No other spider in Quebec has this combination of features. The web is also distinctive — irregular, tangled, and very strong, built close to the ground in dark sheltered locations.

Black Widow Spider — Identification, Venom & Treatment

Overview

The Northern Black Widow (Latrodectus variolus) is the only medically significant venomous spider native to Quebec. While bites are rare — black widows are shy and non-aggressive — their venom is a potent neurotoxin that can cause severe systemic symptoms requiring medical attention. In Montreal and surrounding areas, black widows are found in undisturbed outdoor locations: woodpiles, rock piles, under decks, and in outbuildings. They occasionally enter homes in late summer and fall seeking warmth.

How to Identify Black Widow Spiders

Body size: Female 8–13 mm; male 3–6 mm (males are much smaller)
Colour: Female — shiny jet black with a distinctive red or orange hourglass marking on the underside of the abdomen
Male: Brown or black with red or yellow spots and stripes — does not have the classic hourglass
Abdomen: Round, bulbous, and glossy — very distinctive shape
Web: Irregular, tangled, three-dimensional web built close to the ground — not an orb web
Web texture: Very strong and sticky — noticeably tougher than most spider webs
Behaviour: Shy and reclusive; hangs upside down in its web; retreats when disturbed

Biology & Behaviour

Lifespan: Female 1–3 years; male typically dies shortly after mating
Egg sacs: Female produces 4–9 egg sacs per season, each containing 200–900 eggs
Incubation: 14–30 days
Spiderlings: Disperse by ballooning (releasing silk threads to catch the wind)
Diet: Insects, other spiders, and occasionally small vertebrates caught in the web
Hunting method: Passive — waits in web for prey; injects venom to immobilize
Preferred habitat: Dark, dry, undisturbed spaces — woodpiles, rock piles, under decks, in outbuildings
Seasonal pattern: Most active May through October; may enter structures in late summer seeking warmth

Health Risks & Venom

Venom type: Alpha-latrotoxin — a potent neurotoxin that triggers massive release of neurotransmitters
Bite sensation: Often described as a sharp pinprick; may be initially painless
Latrodectism: The clinical syndrome caused by black widow venom — symptoms develop 30–60 minutes after the bite
Symptoms: Severe muscle cramps and spasms (especially abdomen and back), sweating, nausea, elevated blood pressure, rapid heart rate
Duration: Symptoms can last 1–3 days without treatment
Medical treatment: Antivenom is available and highly effective; pain management with muscle relaxants
Fatality: Extremely rare in healthy adults; higher risk for children, elderly, and immunocompromised individuals
Bite frequency: Bites are uncommon — black widows only bite when directly pressed against skin

Signs of Presence

Irregular, tangled webs close to the ground in dark, sheltered locations
The spider itself — shiny black female hanging upside down in the web
Egg sacs: Papery, round, off-white sacs suspended in the web
Prey remains: Dried insect husks wrapped in silk in the web
Common locations: Under decks, in woodpiles, in garages, in outbuildings, under outdoor furniture
Entry points: Gaps under doors, around utility penetrations, and through vents

Prevention

Wear heavy gloves when handling firewood, moving rocks, or working in outbuildings
Store firewood at least 6 metres from the house, elevated off the ground
Shake out shoes, gloves, and clothing left in the garage or shed before wearing
Seal gaps under doors, around utility penetrations, and through foundation vents
Keep outdoor areas organized — eliminate clutter that provides sheltered hiding spots
Reduce outdoor lighting near the house — lights attract the insects that spiders eat
Inspect under decks, in crawl spaces, and in outbuildings regularly

Professional Treatment

Professional black widow treatment involves targeted insecticide application in confirmed harborage areas — under decks, in crawl spaces, in garages, and around the exterior perimeter. Web removal is performed as part of treatment. If a black widow bite is suspected, seek medical attention immediately — do not wait for symptoms to develop. Call 514-809-1999 for same-day inspection and treatment.

Call 514-809-1999 Spider Treatment Montreal