Common spiders in Ontario, and how to tell what is on your house

Bridge orb weaver

Larinioides sclopetarius, sometimes called the bridge spider, or the grey cross spider in European guides

The lakeside spider. Grey brown, about 1 cm body, banded legs, a pale cross shaped mark on the back, often dozens in a row under eaves, on railings and on any siding that is lit at night. It repairs or rebuilds its round web at dusk, sits in the hub after dark and tucks into a gap or corner by day. On the building from late May, heaviest July to September. On lit buildings within sight of the lake it is usually the main source of the webs and the dark spotting (spider droppings) on light siding, with the furrow orb weaver and the common house spider adding to it.

Bite: not a concern. It runs rather than bites.

Common house spider

Parasteatoda tepidariorum

Small, round bodied, mottled brown, 5 to 8 mm, with a tall rounded abdomen and thin banded legs. Builds the messy tangled cobwebs in porch ceilings, window corners, under deck rails, in garages and behind shutters, and leaves old webs full of debris and small brown papery egg sacs hanging in the web. Several generations overlap, so new webs appear within days of old ones being cleared. Active all season outdoors and all year indoors, and with the bridge orb weaver it accounts for most of the webbing we vacuum off a house.

Bite: very rare and mild.

Cross orb weaver

Araneus diadematus, also called the European garden spider

The big wheel web across a doorway, between a porch post and the eaves, or over a window in late summer. Fat bodied, 1 to 2 cm, brown or orange with a row of white dots forming a cross on the back, and alarming in September because it has been growing all summer. A European species now common across southern Ontario. It sits head down in the hub of the web by day, which makes it the easiest orb weaver to photograph and identify.

Bite: only if squeezed, mild and local.

Barn orb weaver

Araneus cavaticus, the barn spider

The spider from Charlotte's Web. Large, up to 2 cm, plain hairy brown or grey with a darker pattern on the abdomen, and the one that builds the big web on the porch light, the garage door frame or the eaves of a barn or cottage in August and September. Unlike the cross orb weaver it hides in a crack, under a rail or in a soffit gap by day and sits in the web after dark, so people see the web every morning and rarely the spider.

Bite: only if squeezed, mild and local.

Spotted orb weaver

Neoscona crucifera

The other large brown orb weaver on houses in late summer, 1 to 2 cm, hairy, with a mottled or spotted abdomen and banded legs. Easily confused with the barn orb weaver and found in the same places, under eaves, around porch lights and between shrubs and the wall. It builds a fresh web most evenings and takes much of it down at dawn, then rests in a curled leaf or a gap in the trim. Most common from August to the first hard frost.

Bite: only if squeezed, mild and local.

Furrow orb weaver

Larinioides cornutus

A close cousin of the bridge orb weaver and often mixed in with it, 6 to 14 mm, found on docks, railings, boathouses and the lake side of homes, and along rivers and marshes. The tell is a dark leaf shaped mark with a scalloped edge down the back, usually on a pale grey or tan abdomen. It hides in a silk retreat in a corner or under a rail by day and sits in its web at night, and is one of the few orb weavers that stays active in cool weather, so it is on buildings from April to November.

Bite: not a concern.

Bold jumping spider

Phidippus audax

Black, chunky, about 1 cm, with white spots on the abdomen and iridescent green mouthparts. It sits on sunny siding, deck rails and window frames, moves in short jumps and turns to watch you, which is why people notice it. No web; it hunts by sight and spins a small silk shelter under trim or in a shutter to sleep in. Active from the first warm days of May into October.

Bite: only if trapped against skin, mild.

Zebra jumper

Salticus scenicus

The small black and white striped jumping spider, 5 to 7 mm, on sunny brick, window sills, stone steps and fence posts from May on. It stalks flies and moves in quick hops, and often comes inside on a sunny window. No web. Harmless and useful, and not something Spider Pros treats for.

Bite: only if trapped against skin, mild.

Running crab spiders

Philodromus

Flat, grey brown or mottled, 5 to 8 mm, with legs held out to the sides like a crab. These are the quick small spiders that dart sideways across sunny siding, fence boards and window frames and freeze when you look at them, and they sometimes come inside through the window track. No web; they hunt by sight and shelter under bark, siding laps and trim. Common from spring to fall and often mistaken for a young wolf spider.

Bite: not a concern.

Grass spiders and funnel weavers

Agelenopsis

The flat sheet webs with a funnel at one end on the lawn, in the foundation plantings and along the bottom course of siding, obvious on dewy September mornings. Striped brown, fast, with long spinnerets sticking out the back, which is the quick tell. Rarely in the open, except for wandering males in September.

Bite: very rare, mild.

Dark fishing spider

Dolomedes tenebrosus

The one that causes the alarm on the lake. Mottled brown with dark banded legs, up to about 9 cm across in a big female, on dock posts, boathouse walls, tree trunks and the lake side of cottages, sometimes well away from water and sometimes indoors. A hunter, not a web builder, and shy. Usually reported to us as a wolf spider. Its cousin the six spotted fishing spider (Dolomedes triton), greenish brown with a white side stripe, lives on the water surface and dock edges and rarely comes onto buildings.

Bite: only if squeezed, brief local pain like a bee sting, no lasting effect.

Black and yellow garden spider

Argiope aurantia, and its striped cousin the banded garden spider, Argiope trifasciata

The big striking one with the thick white zigzag in its web among the tomatoes, the hydrangeas or the tall grass in August, up to 2.5 cm body, black with bright yellow markings. It sits head down in the centre of the web all day and does not move far all season, then leaves a brown papery egg sac the size of a grape in the plants in fall. The banded garden spider is slimmer, striped in yellow, white and black, and common in the dune grass and along the lakeshore. Both stay in the garden and are almost never on the house.

Bite: not a concern.

Flower crab spiders

Misumena and relatives

Small, 4 to 10 mm, with the front two pairs of legs long and held out like a crab. They sit in flowers, often white or yellow to match the petals, and ambush bees and flies that land. The goldenrod crab spider can slowly change colour between white and yellow over several days. They stay in the garden and the goldenrod along the ditch and are not a house spider.

Bite: not a concern.

Marbled and shamrock orb weavers

Araneus marmoreus, Araneus trifolium

The pumpkin orange marbled orb weaver and the pale shamrock orb weaver build big webs in shrubs and tall grass in September and October and hide in a curled leaf. The marbled one is the October identification question. Rarely on the house.

Bite: not a concern.

Wolf spiders

Lycosidae

Ground hunters, brown and hairy, 0.5 to 2.5 cm, under mulch, stones and the deck. The female carries her egg sac behind her and then her spiderlings on her back. They come indoors through door sweeps in September. The old reports of flesh destroying wolf spider bites came from South America and have been discredited.

Bite: only if squeezed, brief local pain like a bee sting, no lasting effect.

Long bodied cellar spider

Pholcus phalangioides

The long legged "daddy longlegs" living year round in the basement, garage and crawl space, hanging upside down in a loose web. The story that it is the most venomous spider but cannot bite you is false on both counts: it can bite, barely, and the effect is a brief tingle. The name daddy longlegs is also used for harvestmen, which are not spiders and have no venom at all, and for crane flies, which are flies.

Bite: not a concern.

Barn funnel weaver

Tegenaria domestica

The big brown basement spider. Striped head, long legs, 1 cm body, in a flat sheet web with a funnel in basement corners, window wells, garages and crawl spaces, year round. This is the spider people report as a hobo spider or giant house spider. The hobo spider does not occur in Ontario, and health agencies have dropped its bite reputation anyway.

Bite: not a concern.

False black widows

Steatoda borealis, Steatoda triangulosa

The usual black widow false alarm. Glossy dark brown to black, 4 to 10 mm, round bodied, in a tangled web under siding trim, in window wells, garages and basements. The northern false widow has a pale line along the front of the abdomen; the triangulate cobweb spider has a zigzag of cream triangles down the back. No hourglass.

Bite: rare, a sharp local sting that fades in a day.

Yellow sac spider

Cheiracanthium mildei indoors; the native Cheiracanthium inclusum is mostly outdoors

Pale yellow or greenish, 6 to 9 mm, no web, hides by day in a small silk sac in the top corner of a room or behind a picture and hunts at night. Of the spiders found in Ontario homes this is the one most often confirmed as a biter, usually when trapped in bedding or clothing. The bite is a sharp sting that reddens and itches for a few days. Claims online that it rots the skin come from old case reports and have not held up: in verified bites no tissue damage has been found.

Bite: possible, mild, the one worth knowing by sight.

Eastern parson spider

Herpyllus ecclesiasticus

Black and grey with a white cravat shaped mark down the back, 1 to 2 cm, named for the old fashioned clerical collar the mark resembles. A fast night hunter that spends the day in a silk sac under bark, stones or the siding, and wanders indoors in fall, turning up in sinks, bathtubs, bedding and under clothes left on the floor. No web. Bites usually happen when someone rolls onto one in bed or pulls on clothing it is hiding in.

Bite: sharp, local, no lasting effect.

Woodlouse spider

Dysdera crocata

Red orange head and legs, a dull tan or cream abdomen, and long forward pointing jaws that look out of proportion, 9 to 15 mm. Found under flowerpots, stones, mulch and the bottom step, wherever woodlice (sow bugs and pill bugs) live, because that is nearly all it eats, and sometimes in a damp basement or crawl space. Slow moving by day and often mistaken for something dangerous because of the colour and jaws.

Bite: can pinch if handled, no lasting effect.

Northern black widow

Latrodectus variolus

Found in pockets across southern Ontario, mostly the Lake Erie sand country and oak savanna, with confirmed records in the Pinery and Grand Bend dune area in Lambton County and scattered finds further north. It likes dry, undisturbed cover: woodpiles, stone walls, stumps, the underside of furniture left out all winter. Glossy black with a red hourglass on the underside that is split into two triangles that do not touch, and usually a row of red spots down the top of the abdomen. Males and juveniles are smaller, striped brown, white and red, and rarely recognized. The black widows most Ontarians actually encounter are western black widows arriving in grape bunches from California and Mexico, with an unbroken hourglass.

Bites are rare. The spider is shy and bites only when pressed against skin. If you think you have one, photograph it from a distance and call us.

Bite: the only Ontario spider whose venom can make you ill. Symptoms are pain spreading from the bite, muscle cramping, sweating and nausea over a few hours; it is very rarely life threatening and treatment is supportive. If you think you were bitten, call the Ontario Poison Centre at 1-800-268-9017 or go to emergency, and bring a photo of the spider if you can.