Orb weaver spiders (family Araneidae) are known for spinning the classic, circular spiral webs seen worldwide. These large, often brightly colored arachnids construct intricate, expansive webs, sometimes measuring up to three feet in diameter. The orb web design is highly effective for capturing flying insects, making these spiders important ecological agents. However, their size and habit of resting at the web’s center make them conspicuous targets and a frequent protein source in many food chains.
Specialized Insect Predators
A significant threat comes from specialized arthropods, particularly Pompilid wasps (spider wasps). These highly adapted predators hunt orb weavers as a living food source for their larvae. The female wasp locates a spider and injects venom to paralyze it without killing it. She drags the immobilized arachnid back to a burrow, lays an egg on its abdomen, and ensures the larva has fresh prey upon hatching.
Other arthropods also prey on orb weavers. Predatory spiders, such as wolf spiders or jumping spiders, opportunistically attack smaller orb weavers or those away from their webs. Scorpions and mantises are generalist predators that consume orb weavers, especially juveniles. Additionally, some mud-dauber wasps specifically collect orb weavers to stock their larval nests.
Birds, Mammals, and Generalist Hunters
A wide array of larger animals consume orb weavers opportunistically while foraging. Birds are significant predators, especially species like wrens, sparrows, and flycatchers, which navigate dense vegetation and pluck spiders directly from their webs. Small mammals, including shrews and mice, consume spiders found in low-lying vegetation or on the ground. Bats, foraging for insects at night, may also accidentally or intentionally catch orb weavers or their webs.
Reptiles and amphibians, such as lizards and frogs, are documented predators, typically capturing spiders during the day or when they drop from their webs. Conversely, in tropical regions, large orb weavers like the Golden Silk Orb-Weaver can inadvertently capture and consume small birds or bats. Although spiders primarily target insects, the strength and location of their webs occasionally lead to this reversed predator-prey scenario.
Avoiding the Menu: Orb Weaver Defense Strategies
Orb weavers have evolved several behavioral and physical mechanisms to reduce predation. A common defense is rapid escape behavior: the spider immediately drops from the web on a silken safety line when disturbed. This quick descent removes them from the conspicuous web and allows them to hide in the leaf litter or ground cover. Juvenile orb weavers also use ballooning, releasing a silk strand to be carried away by the wind to a new location.
Many orb weavers exhibit cryptic coloration or camouflage, such as the brown or gray hues common in nocturnal species, allowing them to blend into structures during the day. Diurnal species often use bright warning colors (aposematism) and spiny abdomens to signal unpalatability to predators like birds. Some orb weavers engage in web shaking or vibrating the web aggressively when a predator approaches, which may confuse or startle an attacker, allowing the spider time to retreat. Nocturnal activity is another defense, as many species only maintain their webs at night, avoiding visual hunters.