There are almost 60 species of orb weaver spiders (family Araneidae) in Ohio. They capture, kill, and eat insects making them an important pest management bio-ally.
This is the time of the year when the females of many species have reached their maximum size. Their gossamer creations are made even more noticeable if cloaked in morning dew.
Orb weavers are so-named because of their circular, wheel-like webs. Their webs are intricately engineered marvels involving both sticky silk to snare their food and non-sticky silk to provide structural support.
Non-sticky structural silk is used for "radial threads" which radiate from a central point like spokes on a bicycle wheel. The same type of silk is also used for "frame threads" which encircle the web like the rim of a bicycle wheel and for anchor lines that attach to static supports such as plant stems or buildings.
The spider starts at the frame threads and spirals towards the center of the web laying down a continuous line of sticky silk known as the “spiral thread.” It's the sticky spiral thread that snares the spider’s prey.
Two of the largest sized orb weavers found in Ohio are the Yellow Garden Spider (Argiope aurantia) and its equally showy cousin, the Whitebacked Garden Spider (A. trifasciata). These are the formal common names for these species that have been approved by the Entomological Society of America (ESA).
Both spiders have several informal common names. The yellow garden spider is sometimes called the black and yellow spider, the zig-zag spider, and a few names I can't share when this big spider suddenly "appears" in its web at face level. The whitebacked garden spider is sometimes called the banded garden spider which I believe is a more descriptive common name.
Both spiders are commonly found in open fields, prairie plantings, and naturalized areas where they attach their webs to upright stems. They appear to have an affinity for late-blooming plant species that have strong vertical stems such as goldenrods (Solidago spp.), ironweed (Vernonia spp.), Joe-Pye weeds (Eutrochium spp.), and others. Presumably, the spiders take advantage of the smorgasbord of insects attracted to the blooms.
Another web characteristic that is shared by these Argiope spiders is the inclusion of dense webbing that is usually spun in a vertical, zig-zag pattern. Early arachnologists named this web embellishment a stabilimentum (plural: stabilimenta) which shares its Latin roots with stability and stabilization. They believed it added structural support given that the spiders are typically found resting in the center of the stabilimentum. However, the exact purpose of this web decoration remains clouded.
A scientific paper published in 1990 proposed that the stabilimentum produced by certain Argiope spiders was used to attract prey. Many insects can see light in ultraviolet (UV) wavelengths that are invisible to our eyes. Certain flowers that appear white to our eyes actually reflect intricate patterns of UV light, ostensibly to attract insects.
The researchers observed that the webs of some Argiope spiders did not reflect UV light. However, the spiders and the stabilimentum blazed like giant neon “eat here” signs when exposed to UV light. They also showed that webs with stabilimenta attracted more Drosophila flies compared to webs without the ornamentation. Presumably, the insects were lured to their doom thinking they are visiting the mother of all flowers!
However, a paper published in 1998 cast some doubt on the prey attraction hypothesis. The researcher proposed that if the stabilimentum was important for prey attraction, starved Argiope spiders would produce larger structures compared to well-fed spiders. But they found no significant differences and concluded that the stabilimenta may be useful for defense against predators.
Indeed, a follow-up study published in 2001 showed that Argiope spiders with stabilimenta in the webs were significantly more likely to survive attacks by predatory mud-dauber wasps compared to spiders without stabilimenta. They speculated the stabilimenta may physically block the wasps, camouflage the spiders, or distract the wasps so the spider can make their escape.
Eating Habits
As with most orb weavers, both the yellow garden spider and whitebacked garden spider practice a "wrap-and-bite" strategy to quickly dispatch large prey such as grasshoppers with minimal risk to the web … and the spider's health. When a victim becomes entangled in their webs, the spiders rush over to rapidly spin their hapless prey while wrapping them in a thick shroud of dense webbing.
After wrapping their prey in silk, they then jab their fangs called chelicerae (singuar: chelicera) through the exoskeleton to deliver a venomous brew containing both neurotoxins to halt the insect's struggling and necrotoxins which are digestive enzymes that dissolve the insect's innards. The spider then hauls its catch back towards the center of their web and attach their bagged victim to their web to await the work of the enzymes. Later, they jab their chelicerae through the silk to enjoy an insect Slurpee.
Other Notable Orb Weavers
Neoscona crucifera does not have an ESA-approved common name, but it’s often referred to as the Arboreal Orbweaver. Spiders in the genus are sometimes called “spotted orbweavers” owing to spots on the undersides of their abdomen that some describe as looking like two broken “L’s.”
Research has shown that arboreal orbweavers prefer to position their webs in lighted areas to take advantage of the light attracting prey; they are commonly found near porch lights. Young arboreal orbweavers are nocturnal. They spin their webs in the evening and consume their webs in the morning. Mature females are found on their webs throughout the day.
Their habit of positing webs near porch lights but not becoming apparent until the females are fully mature means these spiders may “suddenly appear” in some inconvenient spaces such as across doorways. Although the spiders are only around 1/2 – 3/4” from the tips of their legs, they appear much larger when you open an exit door and find one dangling a few inches from your eyes.
Another “in your face” spider now appearing in large numbers is the so-called arrowhead spider (Verrucosa arenata) which also doesn't have an ESA-approved common name. However, the "arrowhead" refers to its arrow-shaped abdomen and is very descriptive. The arrowhead spider has two color-forms: bright red and muted brown.
This orb weaver spider is much smaller compared to Argiope spiders and the arboreal orbweaver. However, it commonly and inconveniently stretches its web across forest trails. I passed through several webs in rapid succession during a hike last weekend and couldn't decide who was more perturbed: me or the spiders. Eventually, I learned to do a better job of scanning the trail ahead.
Trashline orbweavers (Cyclosa spp.) stretch their webs between the branch tips of shrubs. Look closely and you may spot these diminutive spiders in their beautiful orb webs. The silk in their stabilimentum enshrouds the drained bodies of previous victims. This morbid structure is responsible for the "trashline" common name.
The spiders rest in the middle of their trashline. Their small size and mottled coloration make them very difficult to see among their similarly sized and colored bundles of trash. Indeed, research has shown that the trash bundles serve to confuse predators, such as birds and wasps, intent on making a meal of the spider, and the greater the number of bundles, the greater the confusion.
Selected References
Craig, C.L. and G.D. Bernard. 1990. Insect Attraction to Ultraviolet-Reflecting Spider Webs and Web Decorations. Ecology, 71: 616-623. https://doi.org/10.2307/1940315
Blackledge, T. 1998. Stabilimentum variation and foraging success in Argiope aurantia and Argiope trifasciata (Araneae: Araneidae). Journal of Zoology, 246(1), 21-27. doi:10.1111/j.1469-7998.1998.tb00128.x
Adams, M.R. 2000. Choosing Hunting Sites: Web Site Preferences of the Orb Weaver Spider, Neoscona crucifera, Relative to Light Cues. Journal of Insect Behavior 13, 299–305. https://doi.org/10.1023/A:1007771332721
Blackledge, T. and J. Wenzel. 2001. Silk Mediated Defense by an Orb Web Spider Against Predatory Mud-Dauber Wasps. Behaviour, 138(2), 155-171. doi: https://doi.org/10.1163/15685390151074357
Mishra, R., G. Ahmad, S.N. Chaubey. 2012. Study on the Morphology, Feeding Capacity, and Prey Preference of Neoscona crucifera and N. adianta (Orb-Weaving Spiders). Indian Journal of Life Sciences; Varanasi Vol. 1, Iss. 2: 29-34.
