Scorpion tailed spiders and leaf curlers

I love scorpions, and you may have already worked out that I have a soft spot for spiders, so these guys are definitely favorites.

Scorpion tailed spiders (genus Arachnura) are one of those great taxa where the name says it all. They come from one of the most common families of spider, the Araneidae which includes a few of the spiders I have mentioned in previous posts; the St Andrews cross spiders, and the garden and golden orb weavers.

The "tail" is a very elongated abdomen, which looks quite like a scorpion when arched up (but without the sting!). They use their "tail" as a disguise by sitting in the center of the web, tail up and pretending to be a leaf. As always, there are some great photos of them at www.arachne.org.au

I once when collected a scorpion tailed spider from a web, I was so sure that it was a leaf until it moved at the last second. I have found quite a few of these in urban Sydney, so keep an eye out if you're in Eastern Australia!

Scorpion tailed spiders often place debris around themselves to complete the leaf illusion. Most orb weaving spiders will clear our any non edible objects that fall into the web, but a few collect debris and use it to hide in. Another great example of this is the leaf curling spiders that you see every where in Sydney at the moment. These are also in the family Araneidae and there are two main species, one from the Genus Araneus (left) and the other from Phonognatha (right).

They usually collect a leaf and wrap it around themselves as protection. I took this photo to show the effect of urbanisation on spiders, the leaf curing spider has curled itself up in some styrofoam packaging!

Venomless spiders

During my searches I have often seen lots of webs with many small black spiders, all within the same web. But it wasn't until I collected some and put them under the microscope that I identified them as belonging to the family Uloboridae, commonly called Venomless spiders.

Before I began my survey work I hadn't even heard of venomless spiders!

Seeing as most spiders rely on their venom to subdue their prey this made me wonder how these guys manage to catch anything. Apparently they crush their prey with many layers of silk. I wonder why any spider would evolve away from using venom when it seems to work so well? My first guess is that venom is probably very metabolically expensive to produce. So by not producing venom they actually have to eat less prey.

Also, these little spiders are often social (another rare trait for spiders), living together in multiple webs. Maybe this social interaction allows them to catch prey without venom, or maybe the lack of venom allowed them to become social (ie. they couldn't attack each other anymore!).

They are very common in Sydney, and sometimes there are many hundreds of them in one garden, but they are often overlooked. In fact, even most of the published papers about this family are from the 50's and 60's, maybe it's time for another look!

I'm pretty sure that I have only found one species so far, but there is so much colour variation that it's hard to tell.

More cool crab spiders

It's been a little quiet on my blog scene for the last few weeks. It's field work season (yay!) so I'm spending my time out searching for my golden orb weavers and writing up a paper (stay tuned!).

Even though I'm not currently sorting my samples, I wanted to share some more cool little spiders I found a few weeks ago.

I have posted about crab spiders before (don't you think it looks like a Persian rug?) and they are quickly becoming my 3rd favorite family/group of spiders (1st has to be my study species, Nephila and 2nd goes to jumping spiders).

So here are a few more crab spiders which have really amazed me.

First, a tiny little spider from the genus Bominae (that is the head of a pin!)

Now for a closer look, see how the abdomen is like a concertina? I'm guessing this is so that the abdomen can expand when the spider is gravid. I've never seen it in larger spiders so maybe it's a consequence of being very small?

See some much better photos here.

And just quickly, two other species that caught my eye from the Genus Sidymella.

The long arms on these species are used to catch prey as they sit out on the end of leaves or branches. I don't know what the protrusions on the first species abdomen are for, but the second was very cleverly disguising itself as a twig when I found it.

Sometimes I feel a little bad collecting them when they have tried so hard to remain unseen, but it also makes me wonder about all the camouflaged spiders out there that I'm not finding!

Is this spider male or female?

I promised a while ago to explain how to tell the difference between male and female spiders. It's one of the most common questions I get asked, especially by kids when I point out a mummy or daddy spider!
On a side note, I met so many kids during my garden surveys that were fascinated by the spiders we were finding, and asking really great questions too! It really made my day. If these kids keep on asking questions like this about everything they see around them they're going to make great scientists one day.

Anyway back to sexing spiders...hmmm...

Firstly, as you might know, most females spiders are larger than the males. This is called sexual dimorphism and it is a result of smaller males having an evolutionary advantage (ie. they are able to sneak in and mate with the female, or avoid being eaten by her afterwards!).

Here is a photo I took of a very large female of my study species Nephila plumipes. Can you see the tiny little male on the left?

But sometimes the males of this species are also quite large (comparatively). The photo below is a male (right) with an immature female. This large variation in the sizes of males can happen (in an evolutionary sense) when males have an advantage if they are EITHER large (ie. more likely to out compete a smaller male) or very small.

In some species the males are always the same size, or even larger than the females. This photo shows a pair or Garden orb weavers (Family Araneidae, Genus: Eriophora)

The one on the left is the female and the right is the male. The way I can tell is by looking at the palps, the appendages near the mouthparts. The male has large palps with bulbous ends, he uses these to deposit sperm into the female. In comparison the female has long thin palps. 

Females also have a genital opening called the epigynum near the book lungs on the underside of the abdomen (although this is harder to see). In some Araneidae species there is an interesting protrusion from the epigynum, I'm not sure what this is for. This photo comes from the Cross spiders I was studying in Germany, more on that later.