Golden Girl
Think ‘spider web’. The image that most likely springs to mind is the iconic orb-weaver’s snare.
We have at least 27 species of Orb-weaver spiders (superfamily Araneoidea) in our forest. By far the largest is Trichonephila plumipes (Tiger Spider), a member of the family Nephilidae (Golden Orb-weavers). Females can reach 35mm in body length - and that’s not counting the legs!
It’s only the female that can boast this large body size. The male is tiny, just 5mm. In some Nephilidae, the female:male body size ratio is as great as 10x - one of the highest values for all terrestrial animals (Kunter et al., 2019).
We’re near the southern limit of distribution of Trichonephila plumipes. Nonetheless, in most years we see one or two females towards the end of summer.
I’m pleased to report that the species has made an appearance again this year.
The Golden Girl’s Web
To understand a spider, you first need to understand its web. Kunter et al. (2019), note that “spider webs are, in an ecological sense, extensions of a spider’s phenotype” (p.556).
The huge web of the female Trichonephila plumipes is as extravagant as her body. It allows her to snare relatively large prey, making her a voracious predator - befitting her common name Tiger Spider (which is more correctly but prosaically derived from the pattern of stripes on her legs).
The related Trichonephila edulis, which is the same size as Trichonephila plumipes, has even been known to snare small birds such as finches (Whyte & Anderson, 2017, p.12).
Web construction
Photos 1 and 2 show the female and her web, which is nearly 4 metres wide.
Photo 1: The female Tiger Spider suspended in her web. The circular orb is clearly visible together with many straight attachment lines running to neighbouring vegetation.
Photo 2: A side view of the web. A complex array of lines is also attached to the front and back sides of the orb, providing bracing support. A line behind the spider holds the carcasses of her previous meals. Note that the female spider hangs from the underside of the web with her head facing down. Foelix (2011) states that this is the usual orientation of female orb-weaver spiders in the web. The male (the small reddish-brown object near her hind legs) lies on the opposite side.
Hers is a highly attractive web, and in more ways than one. Bees and other flower-visiting insects find the sunlit golden colour visually appealing (Craig et al. 1996), and a recent study suggests that it smells good to them too (Hsiung et al. 2017)! On the other hand, scavenging insects are more likely to be attracted to a second source of olfactory cues – that string of dead bodies suspended from the web, the spider's trash can (see photo 2) (Framenau et al. 2014).
The web consists of a central orb region with supporting lines to neighbouring vegetation (photo 3). It looks to be perfectly located for a trap across an insect flight path!
The spider spends almost all of her time, day and night, in one particular spot within the orb referred to as “the hub”. The hub is located in the upper part of the orb (see photo 3). This location enables her to reach an insect trapped in the web more quickly as she can run faster downwards than upwards (Foelix, 2011). As the lower section of the orb is larger than the upper, prey is more likely to land there simply by chance.
Photo 3: Red lines indicate position and shape of some of the supporting lines (traced from a reconstructed photo stack). Yellow circle surrounds the orb, a much closer spiral weave of silken threads. The spider is indicated in white, in the hub.
Photo 4: The main part of the orb web consists of threads wound spirally into regularly spaced circles. This web spiral is crossed by radial threads which converge on the hub. A solid connection is made at those crossing points. The female always sits at the hub, waiting for flying insects to land in the outer catching spiral, which is studded with glue droplets to trap struggling prey (Foelix, 2011).
Photo 5: The threads that attach the web to nearby vegetation connect to special frame threads on the outer edge of the orb, forming Y-structures. These help brace the web when an insect flies into the catching spiral, preventing it from tearing (Foelix, 2011).
Photo 6: This shot highlights the golden colour of the threads of the web, which gives this family of spiders their common name - Golden Orb-weavers. Our girl is 25mm in body length. The male, which is just to the left of her abdomen is 4mm long.
Prey capture and feeding
I watched the female capturing and eating prey on several occasions - this included flower wasps, european wasps, winged ants, ghost moths and beetles.
Prey Capture
Photo 7 shows the female immediately after she has captured a small flower wasp. The wasp had just become ensnared in the web close to the edge of the orb.
Spiders can detect vibrations in the radial threads caused by the struggling of trapped insects. The female jerks the radial threads, enabling her to determine the exact location of the prey. She dashes along the radial thread that leads directly to that spot (Foelix, 2011).
While the web is sticky, larger insects can generally free themselves within seconds. So the spider has to get there fast.
In this case the spider reached the wasp in less than a second and immediately grabbed it in her fangs. The wasp was making frantic efforts to free itself, bending its body, flapping its wings, and moving its legs (Video 1). The spider had to work hard to prevent it from escaping. Using her fangs, she injected it with venom and the wasp quickly became paralysed (Video 2).
Photo 7: Female spider immediately after capture of small flower wasp - 26/3/25 9:24:17am. Note the small droplets along the spiral threads which make them sticky.
Video 1: Flower wasp making frantic attempts to escape - 26/3/25 9:24:25 - 9:24:52am
Video 2: Wasp’s movements slow as spider’s venom takes effect - 26/3/25 9:25:05 - 9:25:38am
Just one minute after first grabbing the small flower wasp, the spider returns to the hub - her preferred resting place. You can see her disappearing out of frame at the end of Video 2.
Photo 8 shows her back at the hub, clutching her new prey with her mouthparts. The wasp was no longer moving at this stage, having been fully envenomated.
If prey is small or slow moving, like a beetle, the spider may not waste venom on it. She simply holds it in her pedipalps as she returns to the hub.
Wrapping of prey
Now begins the job of wrapping up her prize. She does this partly to ensure it doesn’t escape as the venom wears off, but also to store the prey for later consumption. It will remain perfectly fresh as the neurotoxins in the venom immobilise but do not kill the insect.
This “wrap first - eat second” strategy is particularly important when several prey insects are likely to be caught in the web around the same time. She can park a wrapped prey at the hub while she dashes off to grab a new prize.
This is exactly what happened before the arrival of the small flower wasp featured in Photo 7 and Video 1 and 2. Do you see the larger flower wasp directly below her in Photo 8? I had been watching her feeding on this wasp for several minutes before she was interrupted by the arrival of the small flower wasp - a new meal on offer.
Photo 8: Spider back at hub with small flower wasp in her fangs - 26/3/25 9:27:11am
Here are the details of the wrapping process. You may like to step through Video 3 as you read the text below.
Video 3 shows her wrapping up the small wasp. She is highly skilled and fast. The wrapping job is all over in less than a minute.
At the start, she connects a single silk hang line between the body of the wasp and the overlying web.
She holds the wasp in her pedipalps with the long axis of its body parallel to hers, grabs a bundle of silk threads from her spinnerets with one of her hind legs, lifts it up over the wasp and attaches it. As the first lift is being completed, she repeats the process with her other hind leg. After a dozen repetitions of this alternating action the job is well on the way to completion.
She then uses her pedipalps to push the wasp away from her body a little, letting it hang on that vertical line and continues pulling silk threads from her spinnerets with her hind legs while she turns the wasp around. This gives a tight, strong weave of fibres running in different directions.
Finally, she breaks the hang line, allows the wrapped small wasp to dangle from a thread from her spinnerets and then attaches that line to her web. Good job!
Towards the end of the video she grabs the large wasp from her earlier catch and brings it up to her body to resume eating.
Video 3: Wrapping of small flower wasp - 26/3/25 9:27:23 - 9:28:54
Video 4 shows the spider performing the same job on a different prey item, a scarab beetle. She gets this job done even quicker - within 30 seconds.
Like the wasp, she hangs the wrapped food parcel from a line at the hub for later consumption.
Another prey item - a winged ant - hangs nearby. The occasional movements of its legs show that it is still fresh and alive.
Video 4: Wrapping of a beetle prey 3/4/25 12:31:02 - 12:31:41
Another day, another meal.
I arrived at her web on another morning to discover she had already caught a European Wasp (Vespula germanica) (Photo 9). It was already well wrapped and showed no signs of movement.
While I can’t be sure she had envenomated it before wrapping, that’s the most likely strategy when dealing with a relatively large, venomous prey item like this.
We are very happy to see her catching this introduced pest species!
Here’s another large prey item - a dung beetle (Photo 10). She was well through her meal when I took this shot as the beetle’s abdomen had been detached from its head and thorax.
There is very little wrapping on the beetle’s body - certainly not enough to restrain it. So she must have immobilised it by a jab from her fangs soon after it landed in the web.
And another big one! A ghost moth - probably an Oxycanus sp. (Photo 11). Again she hasn’t wrapped this prey, just paralysed it with a jab. Moths can escape quickly just by losing the scales on their wings that are stuck to the web. So the spider has to immobilise them quickly.
Running Repairs
While the web is strong, when a large insect flies into it it’s likely to sustain damage. Fortunately, the spider has the smarts to repair even large holes.
Here she can be seen doing some web reconstruction soon after she had captured the dung beetle - presumably to repair damage caused by that insect.
She’s working well away from the hub, towards the bottom of the orb (Photo 12).
She is an accomplished seamstress. Steadily criss-crossing between a series of radial lines, she lays down the new, sticky spiral web.
If you watch closely in Videos 5 and 6, you will see her draw each pair of radial lines together before touching down with her spinnerets to glue the new segment of the spiral thread into place. As the stiff radial threads spring back to their original positions, the highly elastic snare lines are stretched taut.
Photo 12: Female spider at the damage site
Video 5: Repairing the web 9/4/25 10:58:17 – 10:59:34
Video 6: continuing repair job 9/4/25 11:03:07 – 11:04:04
Feeding and Digestion
Having caught and wrapped her prey, the spider can finally get down to feeding.
So what does feeding entail for a spider? It’s quite a different process to insects as spiders don’t possess mandibles – the mouthparts that many insects use to bite off and chew their food.
Instead, they first turn their food into a soup outside of their body and suck it up through the mouth for further digestion in the gut.
She regurgitates digestive juices from her gut as she punctures and crushes the hard exoskeleton of the prey using her fangs and paturon – the enlarged basal segment of the chelicerae (seen in Photo 13 of the female holding a European Wasp). The digestive enzymes flow into the prey’s body and break down its soft internal tissues.
The spider progressively sucks the partially digested prey tissue back into her mouth, using her oesophagus and stomach as suction pumps.
This nutritious brew is filtered (it’s a chunky soup with lots of indigestible bits) as it passes through a dense covering of hairs on the maxillae and a second filter in the pharynx, before entering the oesophagus and stomach.
It finally enters the extensive system of blind tubes (diverticula) in her midgut, where digestion is completed (Photo 14).
From the outside there isn’t very much to see when a spider feeds.
She occasionally moves the prey into a different position to jab a different part of its body with her fangs, as seen in Video 7 of her eating a wrapped beetle.
Most of the action is invisible as she pumps out juices from her digestive tract which liquefy the innards of the prey. You can see wet patches appearing on the surface of the beetle as a result.
That’s about it really.
Video 7: Spider digesting a beetle 3/4/25 12:34:39 - 12:35:03
The inconspicuous male
I’ve barely mentioned the other player in this drama - the male spider. He’s been present the whole time I’ve been watching the female (14 days and counting), just lurking in the background. He will however play an indispensable role - as sperm donor - when he gets a chance.
You may have noticed him in earlier shots. Photo 15 shows him (circled) in his usual position, near the top of the hub, at or just above the hind legs of the female. He lies on the upper surface of the web, on the opposite side to the female.
In Photo 16 he appears to have woven a web of his own. Strands of thin, white silk run from his mini-web and attach to the main web higher up.
He’s nowhere as colourful as his mate but he does have one stand-out feature - greatly swollen pedipalps (circled in Photo 17), which like all spiders he uses to transfer sperm to the female.
He keeps a low profile, remaining still most of the time in the same location. It’s wise for him to be discreet, as there is a chance that the female will mistake him for prey. In fact, he is missing 3 of his 8 legs, almost certainly due to a previous injudicious mating attempt.
We have previously observed and recorded courtship and copulation in a different orb-weaver spider, Argiope keyserlingi (St. Andrew’s Cross Spider).
In that species, the male makes repeated advances to the female as she sits at the hub, plucking at a nearby courtship line within her web. He eventually rushes towards the female when she responds and they embrace. She holds him tightly to her abdomen, his pedipalps within reach of her genital opening. After copulation is completed, the female pulls the male up to her mouth, jabs him with her fangs and eats him. Job over!
Trichonephila plumipes (Nephilidae) belongs to a different family to Argiope keyserlingi (Araneidae), so its mating behaviour may well be very different.
The closest I have yet seen to possible courtship behaviour in the Golden Orb-weaver is shown in Video 8.
The male has apparently constructed a web leading downwards from his normal resting position towards the female and is plucking on some of these threads. The female made no discernible response.
If I’m to observe the actual mating event, I’ll have to be both patient and lucky - just like the little guy. It happens only once and probably doesn’t take long. In Argiope it was all over in 10 minutes.
Video 8: Male spider making advances to female. 26/3/25 9:21:38 - 9:22:07
Uninvited Dinner Guests - Kleptoparasitic Flies
The web was host to some additional dinner guests - numerous small black flies. You may have noticed them in Video 8, crawling around on the web below the male spider.
These spiders are seriously small - no more than 1.5mm long. While they might appear to be trapped on the web, they can in fact move around freely on the silk - perhaps because they keep within the hub, where the threads are not sticky.
Video 9 shows one of these flies hovering near the wrapped wasp dangling from a thread, while two others can be seen on the wasp being held by the spider.
Video 9: Three flies attracted to the spider’s prey. 26/3/25 9:31:07-9:31:16
Photo 22 shows several of these flies feeding on one of the spider’s stashed prey.
They appear to be imbibing fluids from wounds on the wasp - as judged by their swollen abdomens and bubbles of clear fluid in their mouths.
I suspect these may be chloropid flies (family Chloropidae). Marshall (2012) states that – “Some species in the large chloropid genus Olcella are kleptoparasites that aggregate and mate while feeding on juices flowing from some kinds of insects captured by and consumed by spiders.” (p.371). While Olcella is a North American genus, these flies are strikingly similar in appearance and behaviour.
Update: these flies have since been confirmed on my iNaturalist observation as members of the subfamily Oscinellinae (family Chloropidae).
Photo 22: Several flies feeding on a paralysed flower wasp - 26/3/25 9:27:17am
References:
Craig, C. L., Weber, R. S. and Bernard, G. D. 1996. Evolution of predator-prey systems: spider foraging plasticity in response to the visual ecology of prey. The American Naturalist. 147: 205-229.
Foelix, R.F. 2011. “Biology of Spiders” 3rd edition. Oxford Univ. Press
Framenau, V.W., Baehr, B.C., & Zborowski, P. 2014. A Guide to the Spiders of Australia. New Holland Publishers, Sydney.
Hsiung, B-K., Justyn, N.M.,; Blackledge, T.A. & Shawkey, M.D. 2017. Spiders have rich pigmentary and structural colour palettes. Journal of Experimental Biology. 220 (11): 1975–1983. doi:10.1242/jeb.156083 (open access)
Kuntner, M. et al. 2019. Golden Orbweavers Ignore Biological Rules: Phylogenomic and Comparative Analyses Unravel a Complex Evolution of Sexual Size Dimorphism. Systematic Biology 68 (4): 555-572
Marshall, S.A. 2012 “Flies. The Natural History & Diversity of Diptera.” Firefly Books.
Whyte, R. & G. Anderson. 2017 “A Field Guide to Spiders of Australia”. CSIRO Publishing.