Spider explosion

Mangroves covered in spiderweb
Mangroves covered in spiderweb

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.)

Looking into the web ...
Looking into the web …

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.

Tetragnathidae
Part of the web on my second visit

 

The Australasian Darter is a handsome bird …

darter on branch
The Australasian Darter is a handsome bird …
darter on branch
… although some may feel that her enormous flappy feet detract from her dignity …
darter on branch
… while turning round can be a graceless affair …
darter on branch
… and stropping that imposing beak can bring out a surprising resemblance to dinosaur ancestors.

I stopped at Sandy Crossing, where Queens Road crosses Ross Creek, on Friday afternoon and saw this Australasian Darter (Anhinga novaehollandiae) drying her wings at the water’s edge, shrugging them out like washing on a line as they do.

After a few minutes she flew up onto a lowish branch of a nearby gum tree.

I couldn’t help taking a series of photos. They are best viewed in the lightbox – click on any one of them for a larger image, as usual, and scroll through.

The species was formerly known as the Australian Darter, Anhinga melanogaster, but, as Birds in Backyards notes, what used to be one species is now three and A. melanogaster is now only the Asian branch of the family.

 

 

 

 

Butterflies beside Ross Creek

chequered butterfly
Dainty Swallowtail

The Dainty Swallowtail, Papilio anactus, is one of the smallest members of the swallowtail family but still a large and attractive butterfly.

This overview page shows the other members of the family but not all to the same scale. In reality, the birdwings are clearly the largest species at about 110 mm wingspan, followed by the Ulysses and the Orchard Swallowtail, and so on down to the Graphium species, the Clearwing and the Dainty at about 70 mm. Most of Australia’s 17 species of swallowtail live in North-east Queensland and many of them are common (but still special) in our gardens.

I photographed this particular Dainty Swallowtail beside Ross Creek a couple of weeks ago. There weren’t many other butterflies around at the time and most of them were Migrants:

yellow butterfly on small white flowers
Migrant feeding on mangrove flowers

I posted this photo of it because it’s such a good demonstration of the way these light yellow butterflies vanish amongst bright green leaves; even knowing it was right in the middle of my photo, I have looked straight past it several times. What happens, I think, is that the pale yellow reflects the green of the leaves around it, helping it to blend invisibly into the foliage and offering it some protection from hungry birds.

We have four species of Migrant here (Catopsilia spp.). They are all very similar – pale yellowish with some darker markings and a wingspan around 60 mm – and they show seasonal variation and gender differences which complicate identification, but I am fairly sure this one is a Lemon Migrant, Catopsilia pomona.

In other news …

There are two new posts on the Wildlife Queensland Townsville Branch blog which I thought deserved a mention because they fit so well with what I have been doing here on Green Path.

The first records a field trip (they are a monthly activity of the branch and I have been on several this year) to a park I visit often, Lou Litster Park which follows Ross Creek either side of Queens Road. From urban wasteland to city oasis, however, does something I couldn’t, presenting the park’s history as a long-term revegetation project. The project was led by Christine Dalliston and Lynn Saunders who acted as guides on the day, so WQ members learned a lot about how its present state was achieved.

There are some nice photos there – not mine, because I wasn’t able to go on the trip – but I thought I might add here a flower which is mentioned there but not shown, the unusual blossom of the Leichhardt tree, Nauclea orientalis.

spiky brown and cream flower
The chestnut-like flower of the Leichhardt tree, around golf-ball size

The second post, What’s in your [Mundingburra] backyard, is even closer to home in two ways: the photos in it are my own because I was invited to drop by with a camera and see if I could get a few good portraits of a curlew family, and the location is within very easy walking distance.

Curlews (more correctly Bush Stone-curlews, Burhinus grallarius) are common enough in our suburb but it is rare for the history of a particular breeding pair to be so well observed over such a long period and the account is well worth reading.

Ross Creek mangroves and birds

mangroves with stilt roots in water
Mangroves – not a million miles from the city

One of the nice things about Townsville is the network of parks threading through the suburbs. Some of them seem to have no particular reason for existence until the wet season arrives and they become floodways for a day or two, but the most important network is associated with Ross River; the parkland along its banks is almost continuous from the Dam down to the city, and bike paths run through most of its length.

The city centre, however, is not on the river but on a tidal mangrove creek, Ross Creek, which runs from Hermit Park past the Civic Theatre to the ferry terminal; this map may make the situation clearer. Its inland end looks like it connected to the river not too long ago but the river banks have been built up and the creek now just peters out in parkland.

Between them, the River and Ross Creek are wonderful wildlife corridors between the coast and the inland. Vegetation corridors, too, bringing the rich mangrove eco-systems right into the suburbs. The photo above was taken on the upper end of Ross Creek, where Queens Road crosses it. I stop there often on my way home from the city if I have spare time, because fifty metres from the road might as well be a couple of hundred. My last two visits rewarded me with photos of Brown Honeyeaters, a Great Egret, a flock of Little Black Cormorants and a ding-dong battle between a two crows and a brahminy kite.

small olive-brown bird in branches
Brown Honeyeater in the mangroves
Great Egret taking to the air
Great Egret taking to the air
birds against the sky
Little Black Cormorants

The cormorants were just passing through (this time, anyway – a year ago I saw a similar flock on the ground here) but I was able to watch the other two for much longer. I sat for twenty minutes on a low branch of the mangrove tree which the Brown Honeyeater was treating as his home base, repeatedly flying off and returning to sing; and on my next visit I followed the Egret quite a long way upstream as he fished in the shallows, flew a few metres and resumed fishing.