Meanwhile in Cape Town … the spider invasion

Friend Jane says there’s been an influx of Nephila fenestrata, the black-legged golden orbweaver, into suburban Cape Town. Where she lives, the strong webs of these spiders are being strung across walking paths as well as gardens. Luckily, it’s easy to gently reposition them manually, and the spiders aren’t disturbed.

Nephila fenestrata

Nephila fenestrata female, ventral view; photo by Jon Richfield, Wikimedia Commons

nephila_fenestrata_black_legged_golden_orb_web_spider_jonrichfield

Female, dorsal view; photo by Jon Richfield, Wikimedia Commons

She says:

It’s only recently that they’ve decided to go suburban but they seem to be in many gardens now, although not in quite such rampant numbers as mine – people are beginning to come and take pictures.

These spiders are native to southern and eastern Africa. You can see a photo of the large and strong web at Biodiversity Explorer, which says:

Nephila fenestrata, the black-legged nephila, occurs over most of South Africa, excluding the arid central and western regions, and is the only species of Nephila to occur in the Western Cape. Since 2002 this species has crossed over the Hottentots Holland mountain range and is now the most commonly seen orb-web spider on the Cape Peninsula. It can be seen from January till the end of June or even to the end of August, usually in forested areas or near areas with trees allowing for suspension of their large orb-webs. In Kirstenbosch and Newlands Forest one can easily see 30 or more of these spiders on a walk.

Wikipedia says of Nephila in general:

The webs of most Nephila spiders are complex, with a fine-meshed orb suspended in a maze of non-sticky barrier webs. As with many weavers of sticky spirals, the orb is renewed regularly if not daily, apparently because the stickiness of the orb declines with age. When weather is good (and no rain has damaged the orb web), subadult and adult Nephila often rebuild only a portion of the web. The spider will remove and consume the portion to be replaced, build new radial elements, then spin the new spirals. This partial orb renewal is distinct from other orb-weaving spiders that usually replace the entire orb web. In 2011 it was discovered that the web of Nephila antipodiana contains ant-repellent chemicals to protect the web.

Typically, the golden orb-weaver first weaves a non-sticky spiral with space for two to twenty more spirals in between (the density of sticky spiral strands decreases with increasing spider size). When she has completed the coarse weaving, she returns and fills in the gaps. Whereas most orb-weaving spiders remove the non-sticky spiral when spinning the sticky spiral, Nephila leave it. …

The circular-orb portion of a mature [US] N. clavipes web can be more than 1 metre across, with support strands extending perhaps many more feet away. In relation to the ground, the webs of adults may be woven anywhere from eye-level upwards high into the tree canopy. The orb web is usually truncated by a top horizontal support strand, giving it an incomplete look.

Adjacent to one face of the main orb there may be a rather extensive and haphazard-looking network of guard-strands suspended a few inches distant across a free-space. This network is often decorated with a lumpy string or two of plant detritus and insect carcasses clumped with silk. This ‘barrier web’ may function as a kind of early-warning system for incoming prey or against spider-hunting predators, or as a shield against windblown leaves; it may also be remnants of the owner’s previous web. At least one reference explains the suspended debris-chain as a cue for birds to avoid blundering into and destroying the web.

Indeed, some webs have captured small birds, but no one’s found that the spiders actually eat the birds.

I’m particularly fond of the species name for this spider as it is a Latin version of my surname 🙂

Jane says it’s on for young and old in a small patch in her garden:

I would never have thought 4 square metres could have held such variety. I was out in front chatting to my neighbour about how one of the nephila orbs had caught a gecko lizard and sucked out all its juices, leaving the dehydrated corpse in the web, which she’s still fiercely guarding. ‘Look,’ says Louise, and lo and behold behind that orbweaver a praying mantis is stalking a white butterfly – such drama – but the butterfly did escape.  Some butterflies have flown smack into the orbweaver’s curtain, but a surprising number manage to avoid it. A gorgeous black bumble bee managed to duck and dive, as do most of the damsel flies. Mind you, a little white eye bird (a tiny passerine) nearly copped it, but seemed to have rebounded off the web and got stuck in one of my sheets, which was hanging out to dry. I come indoors from the dazzling display to make a cup of tea and a triumphant jumping spider staggers across the kitchen counter with its trophy, a fly bigger than itself. Go spider! I’m having to move strands of orb nearly every morning or I’d be trapped in the house – great colonisers, these ladies.

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