Calls about Spiders

Two of our larger native spiders found in Ohio are orb weavers (family Araneidae) so-named because of their circular (orb) webs.  The webs are intricate structures involving both sticky and non-sticky silk.

The yellow garden spider (Argiope aurantia) is called many names including the black and yellow spider, zig-zag spider, and a few names I can’t share when the big spiders suddenly “appear” at face-level.  I’m using the common name that’s been approved by the Entomological Society of America (ESA) for this species.  Likewise, it’s a similarly showy cousin, the white-backed garden spider (A. trifasciata) is also referred to with many non-approved names such as the descriptive banded garden spider.

Both of these 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 smorgasbord of insects attracted to the blooms.

Orb-weaver spider webs have non-sticky silk used for “radial threads” which radiate from a central point like spokes on a bicycle wheel.  The non-sticky silk is also used for “frame threads” which encircle the web like a bicycle wheel to hold the radial threads in place and to attach the web to supports such as plant stems.  “Spiral threads” are composed of sticky silk arranged in a spiral pattern emanating from the center of the web; it’s the sticky silk that captures the spider’s prey.

A web characteristic that is shared by these Argiope spiders is the inclusion of a vertical, zig-zag pattern of dense silk, called a “stabilimentum,” that is oriented downward from the center of the webs.  Many insects are capable of seeing light in ultraviolet wavelengths that are invisible to our eyes, and certain flowers that appear white to our eyes actually reflect intricate patterns of ultraviolet light, presumably to attract insects.

Research has shown that when some Argiope spiders and their webs are viewed under ultraviolet light; the spider disappears, the web disappears, but the zigzag stabilimentum blazes like a giant neon “eat here” sign.  Insects may be lured to their doom thinking they are visiting the mother of all flowers!

As with most orb weavers, both the yellow garden spider and white-backed 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 (chelicerae plural; chelicera singular) through the exoskeleton to deliver a venomous brew containing both neurotoxins to halt the insect’s struggling and neurotoxins 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 will have jab their chelicerae through the silk to enjoy an insect Slurpee.

The so-called barn spider (Araneus cavaticus) doesn’t have an ESA approved common name but it commonly constructs webs on structures such as barns or homes.  Early risers may become entangled in large, sticky spider webs strung overnight across outdoor doorway openings.  This medium-sized round spider measures around 1/2 – 3/4″ from the tips of their legs.  Of course, they will appear much larger dangling a few inches from your eyes!

The final “in your face” spider appearing in large numbers at this time of the year 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 mutted brown.

This orb weaver spider is much smaller compared to Argiope spiders.  However, it commonly and inconveniently stretches its web across forest trails.  I passed through several webs in rapid succession yesterday 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 orb-weavers (Cyclosa spp.) aren’t typically “in your face” spiders unless you’re sticking your face inside shrubs.  Of course, some of us do as we look closely at plant features.  Look closely between the branch tips of shrubs and you may spot these diminutive spiders in their beautiful orb webs.  The silk in their stabilimentum enshrouds the drained bodies of previous victims; the morbid structure is responsible for the “trash line” common name.

The spiders rest in the middle of their trash line.  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.

Enjoy and Preserve

Spiders eat insects and research has consistently shown they remove a significant number of pests that we would have to deal with otherwise.  Although orb weavers can quickly replace damaged or destroyed webs, we should try and avoid adding to their workload.

On the other hand, if an orb weaver constructs its web in an unwanted location, continually removing the web will eventually cause the spider to take a hint and relocate elsewhere.  If you see the spider on the web, just shoo it off before destroying their web so you don’t accidentally commit and arachnoidal act.