The St Andrew’s Cross spider, Argiope keyserlingi, is very common in our gardens and it is named for its trademark, an “x” cross built into its web, this being the symbol of the Scottish patron saint. (Why? Find out here.)
This mid-sized female, however, wasn’t going to stop with an “x” but had added half of a central vertical stroke and a hint of the other half when I saw her yesterday. Her web is the same today, so that must be how she likes it. Why? No-one knows. In fact, no-one knows why spiders add any of these decorations to their webs.
The decoration, whether it’s a cross (as this ought to be), a loose squiggle (like this, created by a juvenile of the same species, or this, created by an adult of a related species) or any other shape, is called a stabilimentum. The new Whyte & Anderson Field Guide says, “proposed functions have included providing camouflage, making the web more conspicuous to prevent destruction, or attracting insects by reflecting UV light.”
Other orb-weaving spiders add different kinds of solid-looking components to their webs. Cyclosa species, for instance, construct a bar of prey debris across the centre of their web, in which they very deliberately camouflage themselves, but there is no guarantee that this behaviour is related to the Argiope species’ construction of a stabilimentum.
As regular readers will be aware, I like spiders as well as butterflies and birds. I was very pleased when I heard the first hints that a new guide to them might be on the way, the more so since the author-to-be was my regular mentor in all things arachnological through his site Arachne.org and the Spiders of Australia flickr group. When he asked whether he could use a couple of my photos Continue reading “A Field Guide to Spiders of Australia”
I stopped off at one of my inner-city parks three weeks ago and saw the biggest spider colony I’ve seen for quite some time. I was more than slightly boggled by it. Skeins and swathes of web stretched from one mangrove tree to the next along at least 20 metres of creek bank, overhanging the water and within about 1.5 m of water level. (It’s the bank on the far side of Ross Creek from these cormorants.)
When I looked more closely I saw long skinny orange-brown spiders (1), lots of smaller chubbier charcoal-white patterned spiders (2), and a few very small ones (3); also lots of egg sacs woven onto twigs.
I reckoned that (3) were very young juveniles, that most or all of (2) were sub-adults and that (1) were adults, all of one species. “Which species?” is the obvious question. Not so obviously, why did all the adults I photographed happen to be males? Do sub-adult males change from type (2) colours to type (1) with their last moult, I wondered, while adult females remain type (2)?
Identifying the adults to genus level is easy, since the enormous jaws are very distinctive. They are in the genus Tetragnatha in the family Tetragnathidae. Both genus and family have the common names ‘Four-jawed Spiders’ (an exact translation of Tetragnatha) or ‘Long-jawed Spiders’. Beyond that, identification is less certain. They may be Tetragnatha nitens, T. rubiventris or another close relation (follow this link for photos of each species).
On a second vist two weeks later I saw many adult females with the reddish coloration, so any gender imbalance was only temporary. The webs were just as extensive and the egg-sacs even more numerous, although spider numbers seemed to be a little reduced.
I normally see adult spiders in this family as individuals (e.g. this collection), often well away from water and often with hardly any web, let alone a tent city like this. The expert I call on for things arachnological suggested that this could be a local ‘population explosion’, for whatever reason. He hadn’t heard of it with this genus but says it does happen with others, mentioning one of the St Andrews Cross species as an example.
What will happen here remains to be seen. I will call in again and report back … if I emerge alive. I’m just joking, of course – they are completely harmless, and the biggest risk to me is that I will fall in the creek while trying to take a better photo.
Castle Hill dominates the central Townsville skyline but Mount Stuart takes over that role from anywhere further up Ross River. From Mundingburra all the way up to Kelso and across the river to the university and the hospital, Mount Stuart looms large.
That doesn’t mean people visit it very often, of course, but a road leading off the Charters Towers road just beyond the city winds up to a lookout beneath the radio masts. When I drove up a couple of days ago I was welcomed by a resident peacock (perhaps the same one who met me five years ago) and, after taking in the magnificent views over Magnetic Island, the Palm group and coastline all the way to Hinchinbrook, I wandered around the loop track.
The summit is a difficult environment for plants and animals alike: very exposed, very dry, and with only a thin covering of soil where there is any soil at all. Vegetation is ‘open woodland’ with a decent covering of tussocky grass, but most of the trees are tiny. Ants seem to be the most abundant invertebrates but there were other insects to be found as well as the spiders which prey on them.
* P.S. The ant has been identified by my friendly local expert as Meranoplus sp.
Lower down the mountain
Conditions half-way down the mountain are not quite so arid and I found more creatures per square metre than on the summit.
The two kinds of paper wasps are the two commonest around Townsville. More about them here and here.
The Spiny Orb-weaver pictured, Gasteracantha fornicata, is usually seen less often than its black cousins, Gasteracantha sacerdotalis, but outnumbered them on this trip.
“St Andrew’s Cross spider” is a common name which is applied loosely to several similar species. Argiope keyserlingi is the best known, A. picta is encountered from time to time, and this one may be unknown to science – which is a little bit exciting.
Golden Orb-weavers (Nephila sp.) are usually very big and not so brightly coloured but I have seen others around 12-15mm, like this one, in Western Queensland – at Aramac and Porcupine Gorge, for instance.
Australia is blessed with more spiders than most people know how to deal with. Add that to our propensity to tell tall tales to impress visitors, our media’s love of lurid headlines and our gradually increasing ignorance of all of our wildlife, and we have a fertile breeding ground for arachnophobia.
It needn’t be like that – really! Spiders, in general, are harmless, timid and predictable, posing far less of a threat than city traffic or even the average rose bush. Let’s look at some of the myths.
Some of our largest orb-weaving spiders, the Golden Orb-weavers (Nephilidae), do occasionally catch birds in their webs – small birds, since big ones would just crash through, wrecking the web in the process.
I wrote about our Golden Orb-weavers only two months ago, so I won’t repeat myself except to link to the photos on Arachne.org of a Nephila edulis eating a bird.
The other spiders known as ‘bird-eating’ are tarantulas and they don’t normally do it because they live in holes in the ground and couldn’t catch a bird in the first place. The Qld Museum’s fact sheet says …
Australia’s tarantulas make a fine hissing sound, hence their other name, Whistling Spiders. They have been called “Bird-eating spider” but that is incorrectly modified from “Bird Spider” which was given because the giant South American spiders resemble a fluffy bird chick.
… although this BBC article describing the world’s largest spiders provides an alternative explanation for the origin of the ‘bird-eating’ myth.
The species name crassipes is Latin for “fat leg” referring to the relatively fat front legs. This spider can attain legspans of up to 22 cm, normally a big adult is about 16cm. Its body length, from eyes to the rear of its abdomen, measures between 6 and 9 cm, making it the largest Australian tarantula. This species is quite shy and normally does not wander far from its burrow.
But what about his photo? Photos don’t lie, do they?
If that’s a man’s hand, the spider would have a body length of 20cm or so. Even the largest South American species seems to reach only(!) 12cm, with a 28cm leg span. Photos do often lie but this one isn’t even a photo: beware the photoshopped image!
Tarantulas are venomous and need to be treated with due caution, but they are very rarely encountered (holes in the ground, remember) and are, anyway, very timid. When people talk about seeing ‘tarantulas’ in or on buildings they are nearly always talking about huntsman spiders.
‘Tarantulas’ (Huntsman spiders)
Huntsmen (some prefer ‘huntsmans’ but I can’t stand it and wiktionary reckons ‘huntsmen’ is okay) are large and hairy but not as large and hairy as tarantulas: body length is up to about 2.5 cm and leg span up to 15 cm. In nature they live under bark and in crevices, which is why they have flattened bodies and sideways-moving legs, and why they are so comfortable behind furniture in our homes. They are sit-and-wait ambush hunters, which is why they are so fast, and primarily nocturnal, which is why we often see them on the wall when we turn the light on at night.
Meter boxes are also good retreats for them, and the meter reader who left the note which is now circulating on facebook (left) probably encountered a huntsman, and probably imagined the ‘red fangs’.
He was perfectly safe, however: huntsmen are not at all aggressive, and not very venomous. Under “Danger to humans and first aid” the Australian Museum’s fact sheet says, “A cold pack may relieve local pain. Seek medical attention if symptoms persist,” i.e. a bite may hurt for a while but there’s no need to panic.
The Redback on the Toilet Seat
There was a redback on the toilet seat,
When I was there last night.
I didn’t see him in the dark,
But boy I felt his bite.
I jumped up high into the air,
And when I hit the ground.
That crafty redback spider,
Wasn’t nowhere to be found.
A redback on the toilet seat is actually not too unlikely in a bush dunny, but the rest of the story is a bit fanciful, let’s say. The Australian Museum fact sheet does, however, take the bites seriously:
Danger to humans and first aid
Redback bites occur frequently, particularly over the summer months. More than 250 cases receive antivenom each year, with several milder envenomations probably going unreported. Only the female bite is dangerous. They can cause serious illness and have caused deaths. However, since Redback Spiders rarely leave their webs, humans are not likely to be bitten unless a body part such as a hand is put directly into the web, and because of their small jaws many bites are ineffective. …
Common early symptoms are pain (which can become severe), sweating (always including local sweating at bite site), muscular weakness, nausea and vomiting. Antivenom is available. No deaths have occurred since its introduction.
Apply an ice pack to the bitten area to relieve pain. Do not apply a pressure bandage (venom movement is slow and pressure worsens pain). Collect the spider for positive identification. Seek medical attention.
But let’s allow Slim Newton to have the last word.
Spiders are both predators and prey and sometimes we see one in each role in the same, fatal, encounter.
The Daddy-longlegs (Pholcus sp.) in these photos lives quietly between my computer and the wall, waiting for anything edible to come by. (It is probably a direct descendant of this family, since there are always a few in the area.) Jumping spiders, on the other hand, are roving hunters and this little brown one (I thought it might be Servaea or Simaethasp. but have been reliably informed it is a juvenile Hypoblemum) was on the prowl when it blundered into a strand or two of web.
That had just happened when, by pure chance, I reached around to plug in a camera lead and saw what was going on. The daddy-longlegs, outweighed two to one, took care to stay at a safe distance as it used those long legs to further entrap its prey in silk. The process took a couple of minutes and the jumping spider never even looked like getting away. When it was secure, the daddy-longlegs finally came down to sink its fangs into its victim.
Most of us, I think, automatically (and not always logically) choose sides in a conflict like this. If it’s between a lion and a deer, we tend to sympathise with the deer; if a kookaburra and a snake, we’re on the bird’s side. Cat and gecko? Bird and butterfly? Bird and spider? We don’t always side with the hunter, or with the hunted, or with the vertebrate against the invertebrate, or the mammal against the reptile. What do we think about spider vs spider? Or spider vs fly? More interestingly, perhaps, why do we think whatever we think?
The other ‘small death’ I saw yesterday was, in fact, spider vs fly: one of our larger jumping spiders, Mopsus mormon, had captured a soldier fly:
Regular readers will know that I visit a bush block on Hervey’s Range, half an hour or so inland from Townsville, fairly often. It’s a great place for spiders, though I’m not quite sure why; earlier visits have brought me the two species of golden orb weavers living side by side which I mentioned here, my only whip spider, my only tarantula and many more. My latest visit brought me these three little ones.
The Horned Triangular Spider, Arkys cornutus, is so attractively bizarre that it is photographed more often than it otherwise would be. This is the first I’ve seen in real life and yes, I photographed it too.
It lurks in foliage waiting for unwary prey to land close enough to be caught between its impressively barbed front legs, so its hunting strategy is the same as the crab (aka flower) and lynx spiders. However, it is not closely related to either of those families but is an orb-weaver (Araneidae, Araneinae) which for some reason has given up weaving.
My next odd little beast is one of those crab spiders (Thomisidae), the Hairy Crab Spider, Sidymella hirsuta. It’s about 15mm long from toe to toe but its body is almost the same size as that of my Arkys.
My third spider isn’t as photogenic as the other two but I thought I should include it because I saw it in the same patch of bushland on the same morning.
It’s a Cyclosa, a member of a genus of smallish orb-weavers with the habit of constructing a messy strand of debris and (sometimes) egg sacs across the middle of their web and pretending to be part of the rubbish. It must be an effective strategy because they are quite common.
Naming the genus is not problematic but even the experts avoid more exact identification, saying things like, “Cyclosa is very diverse in Australia with at least 10 species, currently under revision. At this stage it is not possible to reliably identify Australian Cyclosa to species, with the exception of a few,” and I’m not going to rush in where they fear to tread.
The thread I photographed contains (counting from the top) debris which looks like tiny dead leaves, four pale egg sacs, dark debris, the spider, more dark debris, a bigger pale bundle and a loose bundle of rubbish; the whole thing is only about as thick as a grass stem. Click on the images, as usual, for more detail.