Howdy, BugFans,
Back in 2020, the BugLady wrote about a Southern spider called the Spinybacked orbweaver Spinybacked Orbweaver– A Spider for Snowbirds – Field Station. We have spiny spiders here in God’s Country, too – this summer, BugFan Danielle sent a picture of a northern spinyback species.
The genus Micrathena (the spiny orbweavers) includes about 100 species of woodland spiders, mostly of the New World tropics. Females spin classic, vertical, disc-shaped trap webs and rest on them. The closely-placed (“tightly coiled”) strands of their webs tell us that they are after small prey like tiny moths, gnats, and mosquitoes. One source calls them “tiny, ornate exterminators.” The female consumes the (protein-rich) circular portion of her web at the end of each day and rebuilds on the original framework the next morning. One author postulates that the genus name comes from the fact that the goddess Athena was skilled at spinning and weaving.
There are four species of Micrathena north of the Rio Grande, all of them pointy, which is thought to be a defense against predators. One author described feeling a “deer fly” on his neck and slapping it – hard. It turned out to be a Spined Micrathena, and the force of the swat caused the spines to puncture his skin.
The SPINED/SPINY MICRATHENA/CASTLEBACK ORBWEAVER/SPINY-BELLIED ORBWEAVER (Micrathena gracilis) is found from the Atlantic to the Great Plains, including southern Canada and into Central America. They live in woods, especially oak-hickory woods, and most especially woods near water. They spin webs in open places in those woods and are famous for throwing a long dragline (escape line) from their webs across trails, to the annoyance of hikers.
Females are less than a half-inch long Orbweaver – Micrathena gracilis – BugGuide.Netand are about twice the size as males. Females have five pairs of spines on the abdomen and come in several different color combinations, ? – Micrathena gracilis – BugGuide.Net, Micrathena gracilis – BugGuide.Net, Spined Micrathena – Micrathena gracilis – BugGuide.Net. Here are three glamour shots – Spined Micrathena – Micrathena gracilis – BugGuide.Net. Males are long and flattened, and many have no spines Spined Micrathena male – Micrathena gracilis – BugGuide.Net.
The spiders are small, and so are their webs – they range from three to almost eight inches in diameter and are suspended four to seven feet above the ground in the shade Spined Micrathena – Micrathena gracilis – BugGuide.Net. Webs are generally vertical but could be tilted by 45 degrees. Despite the fact that she will reuse the old framework when she spins her daily web, these spiders are known to wander and will move to a different site every six or seven days.
Females hang “belly up” from the center of the web, camouflaged from both above and below (predators from above see the dark ventral side against the ground, and predators from below see the lighter dorsal side against a dappled sky), monitoring the vibrations of the strands. The Arkansas Arthropod Museum’s article on the Spined Micrathena describes her actions as “slow and clumsy” when an insect hits the web and says that many insects escape. Most orbweavers wrap and incapacitate their prey before biting them and injecting the meat tenderizer, but Micrathenas will bite first and then wrap Micrathena gracilis? – Micrathena gracilis – BugGuide.Net.
Males spin webs as young spiders, but not after they mature – then they hang out near a female’s web, waiting to make their move. Males spin “courting threads” and woo her from there, treading carefully to avoid being eaten in the process (but if they are, their protein will contribute to the development of their eggs). Females create a fluffy egg sac and attach it to nearby vegetation before they die, and the spiderlings exit the egg sac in spring.
There’s a spider called the Labyrinth/Colonial orbweaver (Metepeira incrassata) that lives in multigenerational colonies with its own kin (hundreds and even thousands of individuals) and tolerates other species of spiders on their communal webs. The Spined Micrathena is one of the species that coexists on the borders.
FUN FACT ABOUT THE SPINED MICRATHENA: Do spiders make noise? Not many spiders do, but the Spined Micrathena is one of them! Spiders have respiration organs called book lungs, and the covers of the book lungs are located on the spider’s undercarriage, just south of where the spider’s front section (the cephalothorax) meets its abdomen. When it’s disturbed, a Spined Micrathena can flick its cephalothorax up and down rapidly, which causes the base of the femur to rub on files on the book lung covers, and presto – stridulation (sound made by friction) (like grasshoppers)! The resulting buzz/hiss can be heard by humans up to about two feet away and is thought to be a defensive sound.
The BugLady