I seem to have run out of week. I had a great idea for a Sunday post this week, but I'm not going to have time to write that one. Instead, here's a recent discovery from the backyard.

Recognise the eyes? This must be a male of the same Cycloctenid (scuttling spider) species I uncovered a couple of weeks ago. He's a good deal smaller, and a good deal slimmer than his female counterpart:

If I knew I was going to compare the male and the female I would have tried to get a better comparison shot... male on the left, female on the right

Whenever you see males and females of the same species that look conspicuously different from each other you know that each sex is subjected to different evolutionary pressures. In mammals, if there is a difference in size, males are usually the larger sex. That disparity arises because males fight with each other for access to females and big males do better than small.

In invertebrates (and fish, for what it's worth), the tables are usually turned, with females being larger than males. This pattern probably arises from the different costs that each sex has to bear in creating the next generation - eggs are expensive and sperms are cheap. That bias might be amplified in 'sit and wait' predators like these Cycloctenid spiders. Fritz Vollrath and Geoff A. Parker looked across a host of spider species and found those with relatively sedentary females tend to have smaller males, then set about trying to build a model to understand how that size difference might evolve. It turns out, if females are few and far between then the success of males has more to with the time they spend searching for females than their ability to fight off other males. So, the best bet for a male Cycloctenid that wants to leave descendants might be early maturation, even if the extra searching time that results from it comes at the cost of extra growth.

This male's search seems to be over. I found him about 5 metres from the log that the female in this first post was living under and she hasn't moved since.

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Vollrath, F. & Parker, G. A. 1992 Sexual dimorphism and distorted sex ratios in spiders. Nature, 360, p.156-159. (doi:10.1038/360156a0)

Labels: arachnophilia, Cycloctenidae, environment and ecology, photos, sci-blogs, spiders, sunday spinelessness

Can you guess what these patterns represent?

So, when I found this spider lurking under a log, and couldn't place it into my (admittedly scant) knowledge of spider taxonomy I was very keen to get at least one photo of its eyes (as it turned out, it was also by far the best photo I took of this spider before turning its log back over):

The drive many naturalists have to call each thing by its right name might seem oddly obsessive, but learning a creature's place in nature isn't the same as placing a stamp in the right section of an album. A taxonomic name can be a key to data collected by hundreds of people. In this case, Ray and Lyn Forster wrote about the Cycloctenidae in Spiders of New Zealand. It seems the family is restricted to New Zealand and Australia and has only a few known genera. They are commonly called "scuttlng spiders" because the arrangement of their legs allows them to run sideways as well as forwards and backwards, which means than can rapidly hide from a would-be predator. That's no-doubt a predator avoiding adaptation, but this particular spider was very happy for me to rest a camera directly in front of and get the shot that let me know what I was looking at.

Labels: arachnophilia, Cycloctenidae, environment and ecology, photos, sci-blogs, spiders

I think our backyard's bugs are on to the fact that they are sometimes the subject of posts here at The Atavism. Take last week, it's been months since I took those photos of a leaf veined slug and I hadn't seen another since. But then, wandering home in the dark this week I spotted this eerie outline through a black-lit leaf.

The eerie outline belonged to another leaf veined slug. To help me with another project I might talk about here at some stage, I promptly chucked the slug in a bucket with a nights worth of leaves graze on. Which also gave me a chance to photograph the slug in some nicer light.

Before it made it was back to a nice dark retreat somewhere in a native flax (Phormium) bush:

But the one that really spooked me were those little green spiders I really ought to have sent away to someone who knows their spiders. As soon as I'd submitted that post I stuck my head into that horrid agapanthus and was amazed to see two new green spiders. Over the months since then I've been keeping an eye on them, and there are now about 15 of them eating aphids, spinning retreats and generally hanging out in the sun.

So, it was time for me make a sustainable harvest. On Friday afternoon I grabbed a paintbrush, a few vials of 95% ethanol and some waterproof paper so I could catch, preserve, and document a few of these spiders and send them to Phil Sirvid at Te Papa who is interested in working out which name these guys should have which will in turn hopefully make the observations I continue to make of this thriving little population a bit more useful.

Labels: environment and ecology, photos, sci-blogs, spiders, sunday spinelessness