letting nature back in

The first creature that caught my eye on the first day of 2019 and caused me to pick up my camera, was this garden orb spider. Its complex round web was strung across the vertical spikes of a Common Rush (Juncus effusus) next to our garden pond.

Garden orb spiders (Argiope) occur across the world, including in the Americas, Europe, Asia, Australia and Africa. There are many species in this genus, and I was not able to pinpoint which species this very beautiful garden orb spider is.

This female garden orb-weaving spider has banded colours on her legs that sport delicate sensory hairs. The abdomen is beautifully marked. Spiders have multiple eyes rather than the compound eyes of insects and they have no antennae but have obvious palps that are used when feeding, and used during reproduction in males.

This female garden orb spider waits in the centre of her web ready to attend to any prey that may get caught in the web.

In the photo above, the spider is moving away from the centre in response to a disturbance in the web, but in this instance the potential prey flew off without getting caught and the spider returned to the centre of the web where she spends most of her time waiting.

May orb spiders eat the central part of the web at night and rebuild that section of web again each morning.

This wasp did not manage to escape the web. The spider bites prey items and envelopes them in silk to immobilise them, and usually returns later to eat them.

In the above photo the spider is eating a bug that previously she had bitten and wrapped in silk when it got stuck in the web. The venom she injects into a victim immobilises it. Prior to eating, the spider injects digestive fluid that includes enzymes that liquefy the insides of the prey animal, which the spider eats by sucking the liquid into her stomach.

Many spiders that weave circular (orb) webs include zigzags of thick silk known as stabilimenta. Two vertical zigzags can be seen in the web in the above photograph. It is speculated that stabilimenta serve several functions, which might include providing camouflage or distraction from the spider in the centre of the web, serving as a warning to birds not to fly into the web (and break the web), attracting insects to fly into the web as the stabilimenta reflect ultraviolet light, and also making stabilimenta may be a way of depositing surplus silk and/or stimulating the production of more silk.

Most spiders are harmless to people and should, where possible, be left undisturbed. The intricacy and engineering of the webs are worthy of our admiration. Most spiders benefit gardeners by eating many insects and other creatures that gardeners may consider to be pests. In any event, I found this spider to be an elegant and decorative presence in the garden, albeit surprisingly easy to overlook.

Sources: 

Cates, Jerry. [n.d.] The Stabilimentum:  And some notions concerning its function. http://www.bugsinthenews.com/stabilimentum_and_some_notions_on%20function.htm; Orb-weaver spider. [n.d.]   https://en.wikipedia.org/wiki/Orb-weaver_spider

Posted by Carol