1. The American House Spider (Parasteatoda tepidariorum)

• Classification: Family Theridiidae (Cobweb Spiders or Comb-footed Spiders).

• Appearance: Small to medium-sized. Females (up to 8 mm body length) are larger than males (up to 4.7 mm). They are typically brown, orange, black, or gray with mottled or spotted patterns, often with an off-white abdomen. They have long, thin legs.

• Habitat & Web:

  • Indoors: They are truly synanthropic, meaning they thrive in human structures. They build messy, irregular, three-dimensional cobwebs in dark, undisturbed areas like corners of rooms, basements, closets, window frames, and sheds.

  • Outdoors: Can also be found in protected spots like under eaves or in piles of wood.

• Diet: They are generalist predators, catching a variety of household pests in their webs, including flies, mosquitoes, ants, and sometimes even larger insects like cockroaches. They are beneficial for pest control.

• Life Cycle:

  • Egg Sac: The female produces multiple (up to 17) distinctive, flask-shaped, papery, brown or tan egg sacs, each containing 100 to 400 eggs. These sacs are hung within the web.

  • Spiderlings: After hatching, spiderlings may remain in a "nursery web" for a few days before dispersing.

  • Dispersal: They often disperse by ballooning, where they release a strand of silk and are carried by the wind to a new location.

  • Lifespan: Adults can live for over a year, sometimes up to two years, with females living longer than males.

• Toxicity: Harmless to humans. They are non-aggressive and will only bite if severely provoked or accidentally pressed against the skin. Their venom is not considered medically significant.

2. The Barn Funnel Weaver (Tegenaria domestica)

• Classification: Family Agelenidae (Funnel Weavers).

• Appearance: A medium-sized spider (females up to 12 mm body length) that is typically brown with a gray chevron pattern on its abdomen and often banded legs. It can be confused with other funnel weavers like the Giant House Spider (Eratigena atrica or Tegenaria atrica), which is larger and also introduced to North America, but less common in the colder Alberta climate.

• Habitat & Web:

  • Indoors: Another non-native species common in houses, garages, sheds, and basements.

  • Web: It builds a characteristic sheet web with a silk retreat (a funnel) leading into a protected crevice (a corner, crack, or under an object). The spider waits inside the funnel for prey to land on the sheet.

• Diet: Preys on insects and other arthropods that get trapped on the non-sticky sheet web.

• Life Cycle: The details are similar to other house spiders, with females laying eggs in sacs often hidden within the funnel retreat.

• Toxicity: Harmless to humans. Like the American House Spider, this species is not aggressive and its bite is not considered medically significant.

💡 Important Context for Alberta

• Cold Tolerance: Spiders found indoors in Alberta houses (like the American House Spider and the Barn Funnel Weaver) have adapted to complete their life cycle within the stable, warmer microclimate of human habitation, allowing them to survive the harsh winters.

• Native Species: While these two are often the most common house spiders, Alberta has over 500 known native species, including Wolf Spiders (Lycosidae) and Jumping Spiders (Salticidae) which are also frequently encountered indoors, particularly in the fall when they seek shelter.