Orb weaver spiders are named for the intricate, spiral-patterned, circular webs they construct, which are a highly effective passive hunting tool. As ambush predators, their survival depends entirely on the design of this geometric trap and the abundance of flying insects in their habitat. Their feeding ecology involves a diet centered on common aerial insects, followed by a sophisticated method of external digestion.
The Primary Menu: Insect Prey
The bulk of an orb weaver’s diet consists of small, flying insects that become ensnared in the sticky threads of their large webs. Common targets include house flies, mosquitoes, moths, and various small beetles, which are captured opportunistically. The spider’s diet is a reflection of the insect population passing through the web’s location, making them generalist predators.
Prey size is a limiting factor, as the spider must be able to subdue the catch without excessive risk to itself or its web. While most meals are significantly smaller than the spider, some larger orb weaver species have rarely been documented catching small vertebrates, such as frogs or hummingbirds.
How the Web Becomes a Dinner Plate
The orb web functions as a non-visual trap for flying prey. The structure is built with two main types of silk: the radial spokes and frame lines, which are non-sticky pathways for the spider, and the capture spiral, which is coated in a glue-like substance. When an insect collides with the sticky spiral, the web’s taut lines transmit vibrations directly to the spider, which waits at the central hub or in a nearby silken retreat.
The spider relies on these vibrations to locate the struggling prey and gauge its size and activity level. To secure the catch quickly, the orb weaver rushes out and administers a paralyzing bite using its fangs to inject venom. This immobilization is followed by a rapid wrapping technique where the spider uses its legs to spin a shroud of silk around the prey, securing the meal and preventing further web damage.
The Unusual Consumption Process
Once the prey is secured and immobilized, the orb weaver initiates external digestion. The spider’s narrow gut cannot accommodate solid food, so it must liquefy its meal before consumption. This is accomplished by injecting a cocktail of digestive enzymes directly into the prey’s body.
These powerful enzymes rapidly break down the insect’s internal tissues, dissolving the muscles and organs into a nutrient-rich liquid slurry. The spider then uses a sucking motion to draw this liquid meal into its mouth, leaving behind only the hard, empty exoskeleton. This method ensures maximum nutrient extraction from the captured meal.
Dietary Supplements and Water Intake
While insects are the primary food source, the orb weaver’s diet is supplemented by other materials. Water is obtained by drinking dew or rain droplets that collect on the web and surrounding foliage, which is necessary for survival in dry environments. This hydration is often collected early in the morning before the moisture evaporates.
Young orb weavers, or spiderlings, also consume microscopic organic matter, which is important for their survival when insect prey is scarce. Pollen grains and fungal spores snagged on the sticky threads provide a source of protein and lipids. Research shows that consuming pollen can double the life expectancy of spiderlings. Additionally, many species recycle their own web; they consume the old, damaged silk when rebuilding, reclaiming the energy and proteins required for new silk production.