1. Classification & Appearance

Feature Description

Family Theridiidae (Cobweb Spiders or Comb-footed Spiders)

Size Female: The body is about 12–16 mm long, with a large, glossy, spherical abdomen. Male: Much smaller (about 3–6 mm body length) and spindly, looking very different from the female.

Female Colour Deep, glossy black.

Female Markings (Crucial) A bright red or orange hourglass shape on the underside (ventral side) of the large abdomen. Juveniles and some females may also have red or white spots/stripes on the back (dorsal side).

Male Appearance Brown or gray, with distinctive white and yellow or light-colored stripes on the abdomen. They do not have the iconic red hourglass.

2. Habitat and Web

• Geographic Range in Alberta: Primarily limited to the arid grasslands and badlands of Southern Alberta (e.g., in the areas around Lethbridge, Medicine Hat, and Grasslands National Park, which extends into Saskatchewan). They are generally not found in the colder, more northern parts of the province.

• Web Structure: They build messy, irregular, three-dimensional cobwebs near the ground. The silk strands are exceptionally strong.

• Web Location: They choose dark, protected, often undisturbed sites outdoors:

  • Under rocks, logs, or planks.

  • In rodent burrows.

  • Near foundations, culverts, and utility boxes.

  • In woodpiles, sheds, and outdoor furniture.

• Activity: They are primarily nocturnal (active at night). They hide in a silk retreat near their web during the day.

3. Hunting and Diet

• Hunting: They wait for ground-crawling or low-flying insects to become entangled in the sticky silk.

• Prey Subdual: They rush out and use a unique, comb-like row of bristles on their hind legs (a trait of the Theridiidae family) to fling sticky silk onto their struggling prey before delivering a venomous bite.

• Diet: Beetles, crickets, grasshoppers, and other spiders.

4. Life Cycle and Mating

• Sexual Cannibalism: The name "Black Widow" comes from the female's tendency to sometimes consume the male after mating (though this is less common in the wild than in laboratory settings).

• Egg Sac: The female produces several round, pale white, pear-shaped or spherical egg sacs, each containing dozens to hundreds of eggs. She attaches these sacs within her web and guards them.

• Lifespan: Females can live for 1 to 3 years, surviving mild winters in protected locations. Males live for only a few months after maturity.

5. Medical Significance and Interaction with Humans

• Bite Risk: Low. They are non-aggressive and will flee if possible. Nearly all bites occur defensively when a human accidentally compresses the spider (e.g., putting on an old shoe or reaching into a woodpile where the spider is hiding).

• Venom: The venom contains a neurotoxin called alpha-latrotoxin, which affects the nervous system.

• Symptoms (Latrodectism): A bite may feel like a pinprick, but within 20 minutes to an hour, severe symptoms can develop:

  • Muscle pain and cramping spreading from the bite site, often concentrating in the abdomen, back, or chest.

  • Nausea, vomiting, headache, and sweating.

  • The bite itself often leaves little mark but can be debilitatingly painful.

• Treatment: Immediate medical attention is necessary. While fatalities are extremely rare (mostly occurring in the very young, very old, or infirm), pain management and supportive care are required. An antivenom is available but generally reserved for severe cases due to potential side effects.