The case of the shrinking spider

A month ago I noticed an attractively patterned spider hanging in its orb web in my front garden. It reminded me immediately of a few Golden Orb-weavers which I found in Western Queensland last Easter (photos here). Those spiders were fully adult females and smaller than I thought they ought to be, but this one was a little smaller still – not quite as big as the familiar St Andrew’s Cross spider. Here it is:

colourful spider in web
The skein of prey debris in the web is absolutely typical of Golden Orb-weavers

No adult female Golden Orb-weaver should be this small – they are normally among our biggest spiders, with a reputation for eating birds, for goodness sake! Here, to remind you if you didn’t know them, are adult females of our common species: Nephila plumipes and Nephila pilipes.  Could this be a male? I didn’t think so, because the males are tiny brown and black critters like this.

Baffled, I turned to Rob Whyte of Arachne.org, sending him the photo above and two close-ups, front and back views (below). Rob told me the photos

…are of a male, and look to me like Nephila pilipes. The sub adult male can have semi-developed palps and may be bigger than the final moult version. …

Interestingly in species like Nephila which get eaten by the female there is no need for size. A large male may even be a threat. The [evolution of] sexual dimorphism doesn’t seem to be affected by the size of the male, the females seem to be on a different size path, so male genes apparently don’t contribute to that.

Males need to be pretty big up to sub-adult, to be fit for foraging and moulting, but then they turn into a lean mean sex machine able to nimbly navigate the web and other males and the mood of the female (if they try and she is not ready she just eats them).

So there we have it: my spider is an adolescent (in human terms) boy, and when he grows up he will be only about two thirds of this size. I can’t think of any other kind of animal which ‘grows down’ instead of ‘growing up’ – can you?

spider underside
As many orb-weavers do, it was hanging head down with its back to the vegetation
same spider from behind.
View from behind and slightly below

What’s around – mid September 2012

The biggest event in the garden in the last month has been the flowering of our poplar gum, plus the paperbark, macadamia and bottlebrush. All attracted their quota of nectar-feeders – birds and flying foxes as well as insects.

The weather news is simple: we had a little bit of rain which triggered the flowering of our trees, and since then we have had rather warmer nights and slightly warmer days, with slightly higher humidity. Temperatures are now consistently dropping to 16C overnight (not 8 or 10) and going up to 28 in the daytime, and I do mean ‘a little bit’ of rain – the BoM recorded 1.4mm on August 20 and none before or since. The invertebrates have responded to the warmth and food with a surge in numbers and variety:

Butterflies and Moths (Lepidoptera): numerous Chocolate Soldiers and Eurema; a few Varied Eggfly and Evening Brown; and visiting Cairns Birdwing, Orchard Swallowtails and Ulysses. Magpie Moths are common again, and I loved the Zodiac Moth on the poplar gum. Nearer ground level, I spotted a pretty white moth, Amerila rubripes. It does have a ‘common name’ – Walker’s Frother but it’s not well known enough to be a genuinely common name.

hairy orange caterpillars
These very hairy caterpillars fell from the poplar gum and ended up on a weirdly photogenic blue textured glass louvre

Flies and their relations (Diptera): Tiger craneflies are abundant, to the extent that I saw half a dozen mating pairs in half an hour one morning, and the orange-headed Plecia flies are also mating. Our tiny metallic Dolichopodidae are as common as ever, and there are a few blowflies too. Mosquitoes? Yes, unfortunately, but not too many.

Paper wasps on a chain of nest cells
A new, small paper wasp nest. Its structure is enough to identify the wasps as Ropalidia revolutionalis

Wasps, Bees and Ants (Hymenoptera): Honey bees came to the flowering trees and various native bees are also around. The small parasitic wasps (Braconidae) are back, and so are paper wasps and mud-daubers.

Spiders and other Arachnids: The orb-weavers suffered housekeeping agonies from the poplar gum as flower debris kept falling into their webs, making them useless for trapping prey. Spiny spiders and the Silver Orb-weaver are the commonest at the moment, with a few St Andrew’s Cross spiders for variety. Jumping spiders, Lynx and flower spiders are all to be found, too.

Others: A praying mantis was resting on our lounge-room wall last night and I have seen a few dragonflies cruising through our airspace. There very few grasshoppers of any size or variety but lacewings, both green and brown, have been attracted to our lights in the evenings. Of the Hemiptera, my little aqua-legs sap-sucker is back and I have seen a few others; not many, though, and I suspect they are waiting for more new greenery.

Last monththis time last year

Microfauna (2) spiders

Here is my second gallery of little creatures, not insects this time (they are here) but arachnids. No need to worry, though – they are tiny, so small they are completely harmless to us as well as almost invisible.

small grey spider
A very young St Andrew’s Cross spider, Argiope keyserlingi. Her web is faintly visible behind her.

Spiders are more like us than like insects in that they don’t change their form as they grow: they are already recognisably spiders when they hatch from their eggs, and they simply get bigger. However, they have rigid exoskeletons like insects, so they can only get bigger by moulting, and some species change colour as they mature.

The familiar St Andrew’s Cross spider changes colour significantly. The 2mm individual above is the greyish-brown of newly-hatched spiderlings but (if she survives) will turn orange-brown with similar coloured stripes, then the stripes will become more distinct, and finally her background colour will darken. Here is an adult.

Tiny yellow spider on leaf
This tiny spider (head and body about 2mm) built its tangled web across a cupped basil leaf. Theridiidae, Anelosimus group.
small translucent brown spider
Stucco spider or Wall spider, Oecubius species, on a shelf in my workshop. Head and body 2mm.

Some species of spiders just never grow very big, and these two are good examples. The second lives amongst us (if you’ve noticed a wisp of silk in a tiny groove or hollow on your walls or a cupboard shelf, there may well of have been one of these behind it) and has therefore acquired a common name. The first, however, is one of many species living anonymously in our gardens. Saying it is in the ‘Anelosimus group’, as my friendly spider expert did, is about as precise as saying ‘some kind of dog’. It is often the best we can do, however, since so many tiny critters remain scientifically unknown and un-named.

Spider and prey
A small spider (3mm), perhaps Nephilengys sp., with prey which seems to be a plant-hopper.
Spider and prey
Another view – click for larger versions

 

 

 

 

 

 

 

 

 

Deciding whether a particular spider is an adult or not can be problematic unless we recognise the species and know how big they usually grow. In this case, I don’t really know but I’m pretty sure that this is nearly as big as it gets because I would have noticed them in my garden long ago if they grew much bigger. After all, I know the Lynx (pretty photo), Flower Spiders (lots of photos) and Jumping Spiders (lots of photos) well enough, and they are all usually under 8mm.

small square brown spider
Austracantha male, about 2mm square.

Male spiders of most species are smaller than the females, often a lot smaller. This little bloke is the male of the common spiky black and white Jewel Spider or Christmas Spider.  He is about 2mm square, while she is about 8mm. Other examples of this size difference (aka sexual dimorphism): Flower spider and Golden Orb-weaver.

Orb-weaver and tiny spider in web
Just friends: an orb-weaver with a tiny spider of another species, probably a Dewdrop Spider. The larger one is about 8 mm long, so the smaller is only about 1 mm.

If you see a tiny spider in the web of a much larger one, it isn’t always a male of the same species. Dewdrop spiders, for instance, are tolerated in webs of larger orb-weavers (Neoscona sp., about 8mm, is in the background here but St Andrew’s Cross and even the enormous Golden Orb-weaver are known hosts), living on scraps and maybe accidentally-caught tiny prey.

Lynne Kelly has said, in Spiders – Learning to Love Them, that wherever we are in the world there is likely to be a spider within a metre of us. I’m sure she’s right, but would add that the reason we are not constantly aware of them is that most of them are so small.

Midwinter dragonfly

Just for those who have been missing dragonflies …

Dragonfly resting in long grass
Midwinter on Mount Stuart

Even in midwinter we have dragonflies and other insects, even on the very exposed top of Mount Stuart. This photo was taken on almost the shortest day of the year and well into our dry season. I’m not sure whether the cold or the dry has the greater impact on insect numbers, to be honest, but they are well down at this time of year even in sheltered spots like my garden.

On the same visit I saw a hover-fly, an orb-weaving spider or ten (Nephilengys and two species of Leucauge, plus the spiky Austracantha), quite a lot of grasshoppers, an orange and black mud-dauber wasp, some little yellow Eurema butterflies, a couple of spotty moths and one or two other insects. Getting out of the house did me good and the views are terrific, but I have to say that the bug-hunting will be better in a few months’ time.

What’s around – mid January

The wet season I was greeting a month ago has been playing hide and seek ever since. We have had very little rain out of it so far, although areas around Townsville have had a little more, and have been watering our garden most weeks. Insect life in the garden has reacted accordingly: a slight increase in numbers because there’s really not much more food around, and a bigger increase in variety because it really is a change of season.

Large butterfly on pentas
My first female Common Eggfly of the season

Butterflies: some Migrants, Crows and Ulysses, one or two Cairns Birdwing and Blue-banded Eggfly, and the first Eurema and female Common Eggfly for many months; a slight increase in Hesperidae; lots of Pale Triangles; very few Chocolate Soldiers (for the first month I can remember, they don’t outnumber all the rest).

Moths: dozens of little fawn grass moths and a few larger ones which come indoors in the evenings.

Wasps and Bees: the Blue-banded Amegilla are still around, as are the tiny native bees and the Resin Bees. I haven’t seen many Paper Wasps or Mud-daubers, and the number of Ichneumonids has dropped a bit.

colourful jumping spider
Jumping spider, possibly Cytaea sp.

Spiders: the gradual return of the orb-weavers continues with St Andrew’s Cross Spiders joining the Silver Orb-weavers, but we still have no Austracantha. Lots of Jumping Spiders and Lynxes but not as many Flower Spiders as there were a couple of months ago.

Flies: not many, really – not even as many of the tiny green Dolichopodidae as usual. Only the Soldier Flies have maintained their populations.

Other  insects: lots of small Grasshoppers; hatchings of Mantis and Neomantis; a noise of Cicadas – not a deafening one here as it was on Hervey’s Range; a scattering of sap-suckers; a small number of Dragonflies.

Other wildlife: the skinks and geckoes have been very active, and we are seeing lots of little ones of all species. The birds, especially the large Blue-faced Honey-eaters and Friar-birds, have been (frankly) crazy, calling continually and chasing each other round the garden.

I am still discovering new insects in my garden, and learning more about some that I have known for a while. I have become aware of another kind of predatory wasp – Gorytini family – after noticing them carrying their large white prey to their nests. A particular pleasure in the last month has been observing the pretty little Neomantis, watching them from babies to adults. And I have just photographed an insect which looks like a weird cross between a fly (look at those big eyes!) and a wasp (look at those wings and that yellow-banded black body!)

Wasp-like insect
Wasp? Fly? Chimaera?

With the help of my friendly local expert I have identified it as a Hover-fly, probably Ceriana ornata. It is very different from most other Hover-flies, e.g. here, here and here; many of then look slightly bee-like or wasp-like but none of them take the mimicry nearly as far.