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.
Vollrath, F. & Parker, G. A. 1992 Sexual dimorphism and distorted sex ratios in spiders. Nature
, 360, p.156-159. (doi:10.1038/360156a0
Can you guess what these patterns represent?
Well, having read the title of the post you may have guessed that each black dot is an eye. In fact, these pictures all represent the way a particular family of spiders arrange their eyes. For spiders, the eyes are a window into evolutionary history: the ancestor from which all spider species descent had eight eyes, and, although most modern spiders have kept all eight, they arrange them in an astounding number of patterns. Very often, the eyes are the best way of placing an unidentified spider into at family. (These pictures are from Lynette Schimming’s article on BugGuide, they represent the families Ctenizidae (trapdoor spiders), Oxyopidae (lynx spiders) and Scytodidae (spitting spiders) and are Creative Commons by-nd-nc licensed).
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):
There are a couple of families of relatively large ground dwelling spiders in New Zealand, and and first glance I thought this might be a vagrant spider
but the eyes are just all wrong for that placement. I had to dig a little deeper for the answer, but between google and Flickr
I found it. You are looking at a member of the family Cycloctenidae.
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.
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.
I like spiders. I mean I really like spiders. So, even though my recent field trip to the Cook Islands was all about the landsnails, and I collected hundreds of them, I wasn’t going to miss the opportunity to explore a whole new spider fauna.
It would actually have been impossible to avoid spiders in the cooks, blazing a trail through the bush means you find yourself reflexively expelling air and scrapping an unseen web of you every couple of minutes. The web spinning spiders behind these snares are only the tip of the arachnid iceberg though, so today I’m going share some pictures of a spider that takes a completely different approach to getting fed.
That’s Athamas whitmeei, a widespread pacific jumping spider. Quite often my search for arboreal snails on the leaves of shrubs on Rarotonga’s mountains would also turn up these guys with their wonderful orange spots (which are worn only by the males). The one in the photo was actually stalking around our motel unit while I was taking photos of snails so I guess they’re quite happy to adapt to different environments.
Unlike their passive, web-spinning cousins jumping spiders need to go out and hunt their food. As a result they have very good vision. The two large, forward-looking eyes can resolve and image onto their retina which appears to be have four different classes of ‘cones’ (one more than our red, green and blue tuned cells) which may allow them to see a much greater range of colours than ourselves.
Even sharp-eyed hunters can fall prey to other hunters. For mammals and birds choosing where to place your eyes is something of a trade off. Forward facing eyes like Athamas’ help you zero in on your target but limit your ability to see around you. Hence sheep with eyes on the side of their head and wolves with forward looking ones. Athamas as no such trade-off to make, having eight eyes in your body plan leaves a couple spare to point backwards!