Spiders, like other creatures with exoskeletons, can’t just grow steadily bigger as we do. Instead, they have to moult: they grow a new (but still soft) ‘skin’ under their old one, then burst open the old one to step out of it and wait (preferably somewhere safe) for their new skin to harden.
The cast-off exoskeleton (technically called the exuvia or exuviae) is sometimes eaten – it is valuable protein, after all – by its previous inhabitant or a passing predator. Some insects’ exuviae are typically left untouched, however, and may remain for months; cicadas’ and dragonflies’ exuviae are often seen hanging on a twig or grass stem like this.
My photo here shows an attractive little jumping spider, Cytaea plumbeiventris, on a leaf beside a cast-off skin of the same species. I didn’t see it emerge but my guess is that the skin was its own. (If you click on the photo to see it at full size you may be able to see the green of the leaf through the eye-lenses of the exuviae.)
Three years ago I wrote about the clever hideaways constructed by jumping spiders on the trunk of our poplar gum. They are still building them but there’s always something new … one of our current residents has chosen to make its retreat in a broad groove which features orange-brown bark instead of the silver-grey of the larger open expanse of the trunk.
But spider silk is silver-white, so the standard retreat would shine out to predators like a beacon – not a good idea at all. What to do? Colour the silk, of course, to match its surroundings!
I have no idea how it managed to do this – whether it changed its silk during production or scurried round on its new white retreat sticking crumbs of bark to it. Both seem unlikely and if it’s the latter, the crumbs are too tiny to see even under the highest magnification of my macro lens.
To see the spider itself – the Flat White Jumping Spider, Arasia mollicoma – follow this link to my earlier post.
Jumping spiders have a cuteness that most other spiders can’t hope to compete with. They are small (therefore unthreatening), often furry, sometimes colourful, always active and alert. (There’s a great video here of one in explorer mode.) And they have big dark eyes, always a plus in the cuteness race – look at baby animals, for instance.
A year or so ago, I discovered that one local species of jumping spider made a retreat or hideaway on the trunk of our poplar gum. This week I discovered a completely different jumping spider had a differently-constructed retreat in the fork between the stem and leaf of one of our golden orchids:
As usual, just click on any of the pictures for a larger version.
Update, 29.7.12: She is still happily living there today. Update, 10.8.12: She is still happily living there today. A boring life, perhaps, but a life.
A few days ago I showed a fly pretending to be a wasp (at bottom of previous post). On almost the same day I saw a little insect 5-6 mm long scurrying around on the broad strap-like leaf of a lily. It looked like an ant, but somehow not quite right. The camera let me stop it and magnify it, and see that it was in fact a spider.
Merely counting the legs is enough to make that judgement, but we can go further. Looking at the eye pattern (you may need to click on the image to see the detail) puts it into the large family of Jumping Spiders, Salticidae. As roaming hunters, salticids depend totally on good eyesight and their upper central eyes are very large and face forward.
I was quite puzzled the first time I saw one (the one below), almost exactly a year ago: the body is very ant-like and the front end is … bizarre. We expect spiders to have two distinct sections, head (technically ‘cephalothorax’) and body (abdomen) but this one seems to be in three sections, with two fat rods sticking out in front of the head – as big as the head, too. They are actually its jaws, enormously enlarged to give it more of a three-part ant profile.
I haven’t been able to completely identify either of these two. I am fairly confident they are Myrmarachne species but haven’t found any just like them on the web. I don’t feel too guilty about that because there are nearly 80 described species, and more to come, according to the experts. There’s a user-friendly introduction to them here, on the excellent Brisbane Insects site, and some of the species are described here, on Arachne.org (scroll down to Myrmarachne – but detour to Maratus if you want a treat).
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.
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.
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!)
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.