Monday, December 18, 2023

Arabesque Orb Weaver


Charlotte’s Web, a cherished childhood story about a spider who befriends a friendless pig is, for many of us, our first encounter with a spider. Charlotte is often depicted as a black widow, but those of us who understand, and love spiders know she is actually an orb weaver.

Orb weavers are one of the most common spiders found throughout the world with over 2800 known species. They are primarily identified by their elaborate round or “orb-shaped” webs. They are believed to have first appeared on Earth during the Jurassic Period approximately 200-140 million years ago. With such a long ancestry they have certainly had enough time to perfect web building.

Webs are generally oblong in shape and can be quite large with dimensions well over three feet common. Many species of orb weavers add an intricate zipper-like pattern to the center of their web, called a stabilimentum. It is not completely understood what this zig-zag patterns function is. The most popular held opinion is that it acts as an attractant for insects by reflecting UV light, essentially drawing insects into the sticky web. Others believe it is a deterrent by providing a visual for birds and an echo for bats, keeping these winged creatures from flying into the web and tearing it to pieces. Still others believe it acts as a stabilizing mechanism to make the web stronger, and more able to withstand the impact and struggle of large insects. No matter what its intended function actually is, it is a fascinating phenomenon of nature. It is this “writing” in the web than lends us to understand Charlotte was an orb weaver. She was a skilled weaver of messages within the web, and while orb weavers are not going to leave “good pig” messages in their webs, they are going to build master insect traps.

So how does the spider build the web? She releases a strand of silk into the wind hoping it will reach a solid surface where it will adhere. Once attached she will begin creating the outer spokes of the web and then work her way to the center of the web in a purposeful fashion until all the strands of silk are placed in a perfect pattern. These strands are made up of several types of silk. Some have sticky globs of silk to capture her prey, and other strands are not sticky at all, allowing her to navigate her own web without being caught in her own trap.

Many orb weavers consume the remainder of their web each morning in a form of spider recycling. It takes a lot of energy to create silk, so by consuming their leftover silk they have developed a way to reduce the amount of energy they need to create a new one. Plus, the webs are often severely damaged by struggling insects. These shredded webs will not function as adequate bug catchers, so new webs must be formed.

One of the most common orb weavers in Missouri is the Arabesque orb weaver, they are found in a wide variety of habitats, but seem to prefer woodlands. Not as flashy as some orb weavers, like the black and yellow garden spider, she is still beautiful in her own right. Their color may vary from a rich golden-yellow, brown, orange or nearly black. She will have a series of black or dark brown comma-like markings on her abdomen, which are a distinctive identifying characteristic of this species. Like nearly all orb weavers the females are larger than males and will often be spotted resting head down in the center of the web of an evening. During the day, they will look for a retreat away from the web, often in the form of a rolled leaf.

Several years ago I was contacted by author and science teacher Larry Weber about borrowing one of my pictures of a this species for a book he was writing for spiders of the North Woods. I was happy to grant his request and honored to have my photograph featured on one of the pages of "Spiders of the North Woods" This is a great, full color field guide that is sure to help individuals identify whatever spider they happen to come across in the Northern regions of our country. To purchase this valuable guide click the link  Spiders of the North Woods Be sure to look for the arabasque spider on page 114.

The word arabesque describes a graceful ballet movement as well as a highly ornate design consisting of curves and swirls that sometimes intersect. I am not sure I would describe this spider as graceful, and I have certainly never seen one move like a ballet dancer. The second definition of Arabesque is, however, most fitting. The pattern on their abdomen is incredibly detailed and ornate, arabesque-like indeed.

All spiders use venom to capture prey. Orb weavers bite their quarry and inject a tissue dissolving venom before wrapping it up in a silken cocoon to save for later. If large wasps or bumblebees become entangled in the web, she will wrap first and bite later. No sense in risking a sting! The venom will begin dissolving the tissue for her, allowing her to digest her food more readily in the form of an insect slurpee.

I am often asked if these, and other orb weavers are harmful to humans. Beyond causing temporary heart palpitations when you unwittingly become entangled in the web, they are harmless. Will they bite? I always say almost anything with a mouth has the potential to bite, but you are only likely to be bitten by an orb weaver if you harass it or if it somehow becomes caught in your clothing. Bites are harmless, and no more painful or dangerous than a bee sting. If you are allergic to bee venom, definitely be watchful of any symptoms that could indicate a more serious reaction.