Theridium tepidariorum.—This is one of the most common house spiders, and is often found in its webs among rocks, but seldom on plants. The females [(fig. 258)] measure sometimes over a quarter of an inch in length, but may mature much smaller. The legs of the first pair are nearly three times the length of the body. The male [(fig. 259)] is shorter and has longer legs. The color varies from dirty white to almost black. The cephalothorax is yellow brown, and the legs light yellow, with brown or gray rings at the ends and the middle of the joints. In the males the legs are orange brown, darker at the ends of the joints. The abdomen is high in front and narrows toward the spinnerets. In dark and well-marked specimens the abdomen has, on the hinder part, six transverse black marks curved upward, thicker in the middle, and partly connected by black spots at the ends [(fig. 260)]. These marks are most sharply defined on the hinder edge, where they are bordered by silver white. The upper mark often forms a conspicuous black and white spot in the center of the abdomen. In light individuals all the markings are smaller and less definite.

It makes a large web in the corners of rooms, under furniture, and in the angles of fences and between stones [(fig. 255)]. It usually stands in the most sheltered part of the web, where a part of it is more closely woven than the rest, but not enough so to conceal the spider. It occasionally makes the web in an open place where there is no shelter above, and then it sometimes carries a piece of leaf into the web and hides under it, as is the usual habit with some allied species. The webs of the young are usually more regular in form than those of adults (figs. [256], [257]). A male and female often occupy the same web for a long time. The eggs are laid in brownish pear-shaped cocoons, several of which are made in the same season by one spider and hang in the web. This species is found all over the world.

Theridium rupicola.—This resembles closely tepidariorum and is easily mistaken for the young of that species. It does not grow larger than an eighth of an inch long. The colors are like tepidariorum, usually dark gray with black spots, the back of the abdomen sometimes almost white. The legs are distinctly ringed with light and dark. In the middle of the abdomen is a pointed hump, the front part generally black and the hinder part white [(fig. 261)].