The adult female triangulate cobweb spider is 3 to 6 mm long (1/8 to 1/4 inch), with a brownish-orange cephalothorax and spindly, yellowish legs, and tiny hairs.

The round, bulbous abdomen is creamy in color, with parallel purply-brown zigzag lines running front to back.

Below or in its web, there may be many dead insects, ranging from stinkbugs to other spiders including Lycosidae, to large Scutigera and even wasps.

[1] Similar to other members of the family Theridiidae, S. triangulosa constructs a cobweb, i.e. an irregular tangle of sticky silken fibers.

As with other web-weavers, these spiders have very poor eyesight and depend mostly on vibrations reaching them through their webs to orient themselves to prey or warn them of larger animals that could injure or kill them.