Introduction
Orb weaver spiders, belonging to the family Araneidae, are renowned for their intricate, circular webs. Often noticed in late summer and fall when they've reached their largest size and built numerous webs, these spiders play a crucial role in the ecosystem. This article delves into the dietary habits of orb weaver spiders, exploring what they eat, how they capture their prey, and some surprising discoveries about their feeding behavior.
What Orb-Weaver Spiders Look Like
The orb-weaver spider group includes a vast number of species, making it challenging to distinguish them from other spider groups and from each other. The Araneidae family is one of the most variable in size and appearance of all spider families. Like all spiders, orb-weavers have a cephalothorax (a fused head and thorax), an abdomen, eight legs, and fang-like mouthparts called chelicerae. They typically have hairy or spiny legs and a relatively large abdomen that overlaps the back edge of the cephalothorax.
Abdomens vary among species, with some orb-weaver spiders having spiny, smooth, or irregularly shaped abdomens. Most nocturnal orb-weavers are brown or gray, while diurnal species often display bright colors like yellow or orange with black markings. Many orb-weavers are brightly colored, attracting attention as they sit in or near their webs, waiting for prey to become stuck. However, the most noticeable aspect of orb-weavers is often their large, circular webs.
Orb-Weaver Webs: Nature's Intricate Traps
Orb-weaver webs are organized, circular grid structures, resembling the webs often depicted in Halloween decorations. These webs consist of radial strands of silk that look like the spokes of a wheel, connected by numerous concentric circular silk strands. The garden orb-weaver spider's web can be exceptionally large, measuring up to three feet in diameter. Typically nocturnal, many orb-weaver species build or repair their webs at night. Some even tear down and consume much of the web's silk as dawn approaches, recycling the silk proteins.
Orb-weavers are not hunters or wanderers; instead, they remain in or near their web, waiting for prey to become entangled. If the spider moves off the web, it stays nearby, hidden in a protected spot like rolled-up leaves or on a plant branch. The spider remains alert to any prey that becomes trapped, thanks to a trap line of silk that vibrates, alerting the spider to the disturbance.
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The Primary Diet: Insects
Small insects constitute the primary diet of orb-weaver spiders. Flies, moths, beetles, wasps, and mosquitoes are common examples of insects that fall victim to these spiders' webs. The spacing of the sticky catch lines roughly indicates the average size prey they most often capture with orb weavers that usually maintain the original web. When an insect gets caught, the trap line vibrates, signaling the spider to rush to the web. The spider then bites and paralyzes the prey before wrapping it in silk for later consumption. If something inedible becomes trapped, the spider will either ignore it or remove it from the web. Species like the Cross Orbweaver (Araneus diadematus) and Golden Orb Weavers exemplify this feeding behavior.
Larger Prey: Occasional Treats
While insects are the staple, larger orb weavers are capable of trapping and consuming small frogs and even hummingbirds if they venture into the web. This highlights the opportunistic nature of these spiders, taking advantage of whatever gets caught in their intricate traps.
The Hunting Process: From Web to Meal
When an insect gets tangled in a golden orb weaver's web, the spider quickly injects it with venom to paralyze it. It then wraps the insect in silk and carries it to the center of the web. At mealtime, the spider slurps up the insect’s liquified insides. This efficient process ensures that the spider can quickly subdue and consume its prey.
Habitat and Prey Abundance
Orb weavers tend to inhabit locations where there is abundant prey and structures that can support their webs. These habitats include areas around night-lights, tree branches, tall grass, weeds, fences, walls, and bushes. The presence of these spiders is often a good indicator of a healthy insect population in the area.
A Surprising Twist: Orb Weavers as Omnivores?
Recent research has challenged the traditional view of spiders as purely carnivorous creatures. Dr. Dirk Sanders of the University of Exeter, along with Benjamin Eggs from the University of Bern, conducted experiments on juvenile Aculepeira ceropegia and Araneus diadematus spiders. Their findings revealed that orb web spiders choose to eat pollen, even when insects are available. Approximately 25% of the spiders’ food intake was made up of pollen, with the remaining 75% consisting of flying insects.
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Dr. Sanders noted, "Most people and researchers think of spiders as pure carnivores, but in this family of orb web spiders that is not the case." This discovery suggests that orb weavers should be classified as omnivores rather than strict carnivores. The spiders actively consume pollen grains, which are too large to be accidentally ingested during web cleaning. This behavior indicates a deliberate choice to supplement their diet with plant-based resources.
Caring for Orb Weavers in Captivity
For those who find themselves caring for an orb weaver, such as a Cross Orbweaver (Araneus diadematus), feeding them properly is essential. When keeping orb weavers in captivity, offering food a couple of times a week is generally sufficient. They often prefer flying prey like moths and flies over crickets or cockroach nymphs. Mealworms can also be a suitable food source. It’s important to ensure the prey has a soft exoskeleton.
Life Cycle Considerations
Like other orb-weaving spiders, the Cross Orbweaver typically lives for a single season. They hatch in the spring, mature over the summer, and then mate and lay eggs in the fall before dying. If an orb weaver creates an egg sac in captivity, it should be relocated to a sheltered spot outdoors to hatch in the spring when there are plenty of bugs for the spiderlings to eat.
Reproduction and Diet of Spiderlings
Female orb-weavers produce one or more egg sacs, each containing up to several hundred eggs. Baby spiders, called spiderlings, stay together for about a week after hatching before starting their independent lives. While specific dietary needs of spiderlings aren't extensively documented, providing a source of small insects and ensuring a humid environment can help them thrive. Some caretakers suggest feeding them fresh raw shrimp in small quantities as a solid food source.
Preventing Infestations: A Balanced Approach
Preventing orb-weaver infestations is usually unnecessary unless they build webs in areas frequented by people. Reducing the population of pests that serve as food for spiders can help. Limiting outdoor lights at night and using yellow "bug light" bulbs can decrease the number of flying insects that gather outside. Sealing up holes and cracks in the house's exterior can also prevent spiders from entering.
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Orb Weavers and Ecosystem Health
Spiders, including orb weavers, are crucial to the health of the ecosystem. They help keep insect populations in check, preventing any single species from becoming overly dominant. This natural pest control is essential for maintaining balance in both natural and urban environments.