Sunday, November 14, 2010


The triangulate household spider, Steatoda triangulosa.

The triangulate household spider above is a female. Like all spiders she has eight legs and two body segments. Her large round abdomen is decorated with brown triangular spots. She is about 1/4 of an inch long, with bands of darker color at each of her leg joints.

She has just settled into a spot close to the ceiling light outside of my bathroom. She has been there for three days, moving only slightly to change position. Day and night, she hangs upside down from her almost invisible web.

The spider below is a male of the same species. He lives in the vicinity of a framed photograph that hangs in my hall. Triangulate spiders are among the most common harmless household spiders of North America. They were introduced from Eurasia.

Triangulate spiders (and other cobweb spinners in the scientific family Theridiidae) make webs from short stands of sticky spider silk arranged irregularly. Their webs are not the pretty symmetrical kind that garden spiders make, but they work just fine.

Triangulate spiders hang upside down waiting for insect prey -- ants, fleas, ticks, and other tasty things. They rush over to wrap up ensnared prey in more silk, and eventually kill and eat them.

The cobwebs that triangulate spider spin probably got their name from an Old English word for spider, attorcoppe, which was eventually shortened to coppe and led to coppeweb or cobweb. Fans of J.R.R. Tolkien will remember when Bilbo the Hobbit tried to enrage the giant spiders of Mirkwood by jeering at them: "Attercop! Attercop! are fat and lazy, you cannot trap me, though you try, in your cobwebs crazy!"

Abandoned cobwebs gather dust and gradually become more visible. I don't knock them down unless they are empty, not wanting to interfere with the capture and consumption of insect pests. No good housekeeping seal of approval for me -- I harbor cobweb spinners!


  1. I found one of these spiders in my bathroom, thanks for the information! I'm glad it's not poisonous, but it sure is ugly! :)

  2. Once you know they're harmless they are kind of interesting, aren't they?

  3. I was cleaning out a cupboard and found one. I thought it was a brown recluse spider. Thank you so much for the info. There were many egg sacks so I thought I was going to have to burn down the house for a min. Thank you!