The environment: science, ethics and communication
Sitting in the back garden yesterday, I glanced down to see an ant wandering along the edge of my table – or so I thought. But it wasn’t moving like an ant: they are purposeful, even if we may not divine their purposes, and this maybe-not-an-ant was wandering rather slowly and aimlessly. At a closer look, its antennae weren’t very convincing, either Continue reading “The ant that wasn’t”
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? Continue reading “The individualist”
A Field Guide to Spiders of Australia
Robert Whyte and Greg Anderson
CSIRO publishing, 2017
Paperback $49.95; e-books also available.
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.
Conditions half-way down the mountain are not quite so arid and I found more creatures per square metre than on the summit.
