Purseweb spiders are a family of spiders that build tubelike webs; in our area, these webs are usually 6–10 inches long and positioned vertically against the base of a tree. At a glance, the web may look like a small branch leaning against the tree trunk. The spider hides within its tube, waiting for prey. For this reason, purseweb spiders are not often seen; when people do notice purseweb spiders, it is usually males that are wandering around on the ground, seeking mates. Males’ gender can be verified by noting the enlarged, clublike pedipalps to each side of the large chelicerae (fangs).
Species: Eight species of purseweb spiders occur in North America north of Mexico: 7 in genus Sphodros, and 1 in genus Atypus (before 1980, all were placed in genus Atypus). Of the 8, apparently only 3 species in genus Sphodros occur in Missouri; the rest have distributions that don’t include our state.
The redlegged purseweb spider (Sphodros rufipes; previously called Atypus bicolor) is Missouri’s most common purseweb species. It is most abundant south of the Missouri River. Like most other purseweb spiders, it resembles a sturdy running spider but is glossy and has exceptionally large chelicerae. The overall color of males is shiny black with bright reddish-orange legs. Females, less likely to be seen because they usually stay hidden in their camouflaged webs, are shiny dark reddish brown with blackish grooves and depressions, with a dull brownish abdomen.
Fitch’s purseweb spider (S. fitchi) is also found in Missouri; its overall range includes states to our north, west, and south. It is similar to S. rufipes, except the males of S. fitchi have orange (not red) coloration, which is only on the top surface of the outermost leg segments, starting only on the outermost tip of the femur segment. In 2018 this species was found on a prairie in southwestern Missouri.
The black purseweb spider (S. niger) is another species with a rather wide range, extending from the northeastern United States west to Wisconsin and Kansas, north to Ontario, and south to Tennessee. It is all glossy black, except for a gray or pale bluish band crossing the head at the base of the chelicerae.
Length: bodies usually about ½ to ¾ inch long (including chelicerae, but not including legs); females larger, to about 1 inch.
Potentially statewide; they appear to be most common in the southern half of Missouri. Different species have different ranges.
Habitat and Conservation
Different species of purseweb spiders have different preferred habitats and different tubular web-building architecture. Tubes often incorporate organic debris, sand, and/or soil, aiding with camouflage. Most tubes have an underground portion where the spider can retreat during hot, dry conditions.
S. rufipes prefers mixed hardwood forests and builds its webs vertically against a tree trunk, with the toe of the web extending underground along the base of the tree as its roots flare out below soil level. At the top end of the tube, a white sheet of webbing attaches the tube to the tree’s bark.
S. fitchi is associated with dense upland oak-hickory woods on north-facing hillsides; about two-thirds of its 9-inch tube is underground, apparently nearly vertical. It has been collected from a prairie in southwestern Missouri.
S. niger is associated with woodland edges. In the east, this species builds its webs on sloping terrain beneath the leaf litter of pine trees, with part of the tube fairly vertical into the fairly deep, rather moist, partly decayed duff and the “aboveground” portion fairly horizontal, just above the duff layer but still hidden beneath pine needles.
The tubular web of purseweb spiders is key to their hunting technique. Entomologists W.J. Gertsch and N.I. Platnick summarized the strategy well: “insects crawling over the aerial tube are impaled through the silk from the inside by the long, thin fangs and then secured by cutting a rent in the silk large enough to drag the prey through the tube. Once eaten, the remains of the prey, and later the liquid droppings, can be ejected to the outside through an opening at the top of the tube.” Then the spider repairs the hole in the silken tube and waits for more prey.
A study of S. rufipes in the southeastern United States, based on insect remains collected at the bottom of females’ purse webs, cataloged sowbugs, millipedes, crickets, beetles (including longhorn, ground, and scarab types), ichneumons, ants, caterpillars, and spiders (including males of the species). A study of S. niger in Massachusetts showed that species eating mostly millipedes, but also beetles and most likely other spiders, plus sowbugs and centipedes. Because that species’ webs are not visible above ground, flies, caterpillars, and other flying or non-burrowing insects are probably not main prey items.
Along with North American tarantulas, trapdoor spiders, and some other “oddball” groups, purseweb spiders are classified as mygalomorphs. The mygalomorphs are a major division of the spider order, separate from the much larger group called the araneomorphs (“true spiders”). Mygalomorph spiders retain several ancestral (“primitive”) characteristics of their arachnid forebears and have a long fossil history. Mygalomorphs comprise only 8 families in North America north of Mexico; globally, they comprise only about 7 percent of all spiders. Mygalomorphs can have long lifespans and can molt once or twice each year, even after attaining sexual maturity. They have simple silk-making organs, unlike the specialized equipment used by the well-known araneomorphs. Other distinctions include 2 pairs of booklungs (which appear as 4 light-colored patches on the underside of the abdomen; most “true spiders” have only 1 pair), and their chelicerae and fangs align and hinge parallel to the main axis of the body (meaning their fangs stab downward or forward) (whereas “true spiders” have chelicerae and fangs that hinge sideways/perpendicularly, or diagonally to the body axis).
In early summer (usually June), males wander across the ground during the daytime seeking females; this is when most people see purseweb spiders. Apparently the males sometimes are eaten by their intended mates. Females can live 7 or more years. The silken tubes become increasingly tough as the season progresses and its occupant becomes larger. Females create egg cases in their purse webs. In S. rufipes, the egg sac is positioned at the bottom of the tube, below ground. The spiderlings typically hatch in late summer. In some species, the young spiders hatch and disperse in late summer, while in other species, the young may remain with their mother through the winter to disperse the following spring.
Purseweb spiders have large, imposing chelicerae, and like nearly all other spiders, they possess venom to subdue their prey and can potentially bite a human if mishandled. But purseweb spider bites do not pose a danger to people, except for the rare cases of people who are highly sensitive to spider bites.
As representatives of a rather unusual group of spiders (mygalomorphs), and some of the few that occur this far north, purseweb spiders are a curiosity and a natural wonder. The oldest known mygalomorph spider lived in the Triassic period, more than 200 million years ago.
In 1792, the skilled and prolific artist-naturalist John T. Abbot called these spiders “purseweb” spiders for the long, stocking-like purses that were in fashion at that time. Born in London, Abbot moved to America in 1773 and eventually settled in Georgia. Though he is little-known today, he produced more than 4,000 original, highly detailed watercolor paintings of New World plants and animals, especially of insects and birds. Most of these were sold in Europe, and fewer than 200 were published under his name.
S. fitchi was named in honor of Kansas herpetologist Henry S. Fitch, who collected the type specimens for the species in northeastern Kansas in 1961. He is honored in Kansas and nationally for his many, many contributions to the natural sciences.
The red and black coloration of S. rufipes and S. fitchi males may be an example of Batesian mimicry, in which a relatively harmless or helpless species benefits from a resemblance to species (such as ants or wasps) that can sting. The fact that only the males — which must leave the shelter of their tube webs and risk their lives walking around in the open — have this coloration supports this theory.
Herbert Fitch, who collected the type specimen for the purseweb spider that bears his name, observed a jumping spider pounce on and kill a same-size specimen of S. fitchi. The acuity of senses, rapid movements, and ease with which the jumping spider dispatched the purseweb spider led him to note that male purseweb spiders must be extremely vulnerable and experience a high mortality once they leave their tube shelters and go out in the open looking for females.