The openfield orbweaver is a common nocturnal orb-weaving spider in Missouri. Its oval, yellowish, whitish, or tan abdomen with contrasting brownish stripes are key identification characters. The carapace (head), except for the dark area around the eyes, lacks dark markings. The grassland habitat and nocturnal lifestyle are also important clues to its identity.
Similar species: Missouri has 14 species of orb-weaving spiders in genus Araneus, which as a group are sometimes called the "angulate and roundshouldered orbweavers." Another common Missouri member of this genus is the marbled orbweaver (Araneus marmoreus), which is larger and is easy to distinguish by comparing pictures and habitat.
Apart from those two, our other 12 Araneus species are less commonly encountered. Some species in this group are quite difficult to distinguish, even by specialists. For the less common species, you often must observe small details of the anatomy in order to determine the ID.
Missouri has many more types of orb-weaving spiders in addition to those in genus Araneus. See the links at the bottom to browse some of these other species.
Length: about ¼ inch (not including the legs); males are smaller than females.
Statewide.
Habitat and Conservation
These small spiders are common but easily overlooked in grassy fields and prairie habitats and can potentially be seen year-round.
The webs are vertical and only about 8 inches in diameter. This species does not hide in a retreat near the web, waiting for prey to get trapped. Instead, it rests in the web almost all of the time. When disturbed, it drops to the ground.
Food
Flying insects such as moths and flies are the principal prey. Once caught in sticky strands of the web, they are bitten and trussed by the spider, which later eats them.
Life Cycle
In spring, the young spiderlings emerge from their egg case, disperse, and begin building webs, hunting, and growing. Males do not spin webs. Once mature, the males wander in search of a mate, and the females build webs, eat, and wait for a mate. Once mated, the female keeps eating and creates egg cases. The first freezes usually kill all the adult spiders, with only the egg cases overwintering.
Human Connections
The amazing web patterns of orbweavers have fascinated humans for millennia.
E. B. White wrote his classic book Charlotte's Web about a spider in genus Araneus.
Orbweavers control populations of flying insects, many of which are pests.
Orbweavers don't bite unless molested, and their bites are not dangerous, anyway.
Ecosystem Connections
These spiders control populations of flying insects.
Although they may seem ferocious, outside their webs and hiding places these delicate creatures are quite vulnerable to predation themselves. Orbweaving spiders usually have poor vision and are awkward when not in their webs. Also, their egg sacs are relished by many species and provide winter food for many birds.
