Spider-Man uses a line of silk to swing through cityscapes to subdue evildoers. But in the arthropod world, spider-women are the masters of silk. Female spiders have seven silk glands that produce a range of silk types for different purposes, such as constructing intricate webs to snare prey, and wrapping captured victims.
Male spiders have fewer silk glands that are primarily used to produce single-strand draglines, or anchor lines, allowing them to swing free without falling. Marvel got it right. Entomologists watch movies with a different eye.
According to the Annotated List of Ohio Spiders published by the Ohio Biological Survey in 2021, our state is home to 682 species of spiders (order Araneae). Most overwinter as eggs that hatch in the spring, with the spiders developing throughout the season. They reach maturity in late summer to early fall, which is why they are so common at this time of the year.
All spiders share some common eating habits. The business end of their mouthparts are called chelicerae (singular: chelicera), which consists of two parts: a base segment attached to the body and a movable fang. They are called “jackknife” chelicerae because the base segment acts like a jackknife handle and the fangs fold out and in like opening and closing a jackknife blade.
The fangs are hardened (sclerotized) to withstand piercing an arthropod's sclerotized exoskeleton. Spiders drive their fangs through the exoskeleton of their arthropod victims to deliver a venomous brew containing both neurotoxins and digestive enzymes.
The neurotoxins halt struggling with their quarry, and the digestive enzymes dissolve their prey’s innards. After the external digestion is complete, the spider jabs its chelicerae once again into its victim to enjoy an arthropod Slurpee.
Female spiders may be the masters of silk, but female orb-weavers (family Araneidae) are the true spinmeisters of the spider world. They are so named because of their circular, wheel-like webs.
Their gossamer creations are most noticeable if cloaked in morning dew. 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.
Charlotte, in E. B. White’s 1952 classic children’s novel, “Charlotte's Web,” is an orb-weaver. My copy is dog-eared from reading it to my children. Of course, White did not dwell on Charlotte’s eating habits; it would have been a horror story. I always had to improvise by adding that part. For some reason, White’s book was never one of my children's favorite bedtime stories.
Other Notable Orb-Weavers
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).
However, both spiders have several informal common names. The yellow garden spider is sometimes called the black and yellow spider, and the zig-zag spider, but more on that later. Occasionally, the black color is replaced by brown.
The whitebacked garden spider is sometimes called the Banded Garden Spider, which I believe is a more descriptive common name. A faint U-shaped marking is commonly evident on top of the abdomen. However, the common name "U-Spider" could be mistaken for an insult.
Both spiders can measure over 1 inch in diameter from the tips of their legs. They are commonly found in open fields, prairie plantings, and naturalized areas where they attach their webs to late-blooming plant species that have strong vertical stems. The webs can range in height off the ground from only a few feet to just about face-level.
This means off-trail bushwhacking can be a high-risk venture at this time of the year. Unexpected encounters with one of these huge spiders hanging at eye level can be frightening, leading to spastic movements accompanied by high-pitched sounds (personal experience). For some odd reason, my children always found this hysterical.
A 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.
One scientific study published in 1990 pointed towards the possibility that the stabilimentum is used to attract prey. Many insects can see light in ultraviolet (UV) wavelengths, and the researchers observed that the webs of some Argiope spiders did not reflect UV light.
However, 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 were visiting the mother of all flowers!
Other studies point to the stabilimenta serving as a defense structure protecting the spiders from predators. A 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 spiders can make their escape.
The images below seem to support this perspective. They show an immature yellow garden spider and a mature spider hiding behind a massive expansion of stabilimenta.
The Arboreal Orbweaver (Neoscona crucifera) belongs to a genus of spiders sometimes called “spotted orbweavers” owing to spots on the undersides of the abdomen. Some describe the spots as looking like two broken “L’s.”
This is another “in your face” spider for their habit of spinning their webs in places where they are least expected, such as across a doorway. Research has shown that arboreal orbweavers prefer to spin 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 positioning webs near porch lights, and 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 inches in diameter 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 (personal experience). Thankfully, my children only witnessed this one time.
Probably the most cunning “in your face” spider that’s now appearing in large numbers in Ohio’s forests is the Arrowhead Spider (Verrucosa arenata). 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, measuring only around 3/8 inches in diameter. However, it commonly and cunningly stretches its orb web vertically across forest trails where unexpected face-to-face encounters can cause it to grow much larger.
This spider provided endless entertainment for my children during our frequent family hikes in Ohio’s forests, until I started using a “spider stick” to clear our path by sweeping it up and down ahead of me. If you ever see another hiker suddenly launch into erratic, spasmodic movements, come to their aid by offering them a spider stick. Of course, you should first explain why you’re waving a stick at them. Again, my children laughed hysterically.
Thankfully, Trashline Orbweavers (Cyclosa spp.) stretch their webs between the branch tips of shrubs or small trees, out of the way of hikers. You must look closely to 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 or at the end 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.
Arachnophobia
Entomologists watch movies with different eyes. What if Spider-Man had made an appearance in the 1990 cult classic, Arachnophobia? Delbert McClintock (John Goodman) may have sprayed him! Unfortunately, that’s a common response when people encounter spiders. Just like snakes and clowns, people can have an irrational fear of our eight-legged bio-allies.
Of course, part of our fear stems from the fact that spiders do have fangs, and as I’ve described above, their feeding habits are a bit scary. However, the movie was science fiction: Spiders don’t eat people. While a few spiders in Ohio can deliver serious bites, the orb-weavers in this Alert are not among them. The bite of even the largest Argiope spiders would be similar to a bee sting. If you could even get them to bite; I’ve handled them, and they are not aggressive.
More importantly, spiders are allies rather than threats. They eat insects and other arthropods, and play a significant role in suppressing forest, landscape, and agricultural pests. They also eat pests that threaten human health, such as mosquitoes. A paper published in 2017 suggests that the annual worldwide prey kill of spiders ranges from 400 to 800 metric tons. Killing spiders provides a reprieve to insect pests, so we should leave them alone. The same with snakes and clowns.
Selected References
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(3), 299-305.
https://doi.org/10.1023/A:1007771332721
Blackledge, T. A. (1998). Stabilimentum variation and foraging success in Argiope aurantia and Argiope trifasciata (Araneae: Araneidae). Journal of Zoology, 246(1), 21-27.
https://doi.org/10.1111/j.1469-7998.1998.tb00128.x
Blackledge, T., & Wenzel, J. (2001). Silk mediated defense by an orb web spider against predatory mud-dauber wasps. Behaviour, 138(2), 155-171.
https://brill.com/view/journals/beh/138/2/article-p155_2.xml
Bradley, R. (2021). Annotated List of Ohio Spiders. Ohio Biological Survey, Bulletin New Series, 19(1).
https://spidersinohio.net/wp-content/uploads/2022/04/Bradley_2022_Annotated_List_of_Ohio_Spiders.pdf
Craig, C. L., & Bernard, G. D. (1990). Insect attraction to ultraviolet‐reflecting spider webs and web decorations. Ecology, 71(2), 616-623.
https://doi.org/10.2307/1940315
Humenik, M., Scheibel, T., & Smith, A. (2011). Spider silk: Understanding the structure–function relationship of a natural fiber. Progress in molecular biology and translational science, 103, 131-185.
https://www.sciencedirect.com/science/chapter/bookseries/abs/pii/B9780124159068000078
Nyffeler, M., & Birkhofer, K. (2017). An estimated 400–800 million tons of prey are annually killed by the global spider community. Sci Nat 104: 30.
https://link.springer.com/content/pdf/10.1007/s00114-017-1440-1.pdf
Tokareva, O., Jacobsen, M., Buehler, M., Wong, J., & Kaplan, D. L. (2014). Structure–function–property–design interplay in biopolymers: Spider silk. Acta Biomaterialia, 10(4), 1612-1626.
https://www.sciencedirect.com/science/article/abs/pii/S1742706113004121
