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Friday, June 9, 2017

Master spinners of silk: the Orbweavers

The following article was published in Nature News, Midland Express, 6th June 2017.

Local writer Dr. Lynne Kelly shares her love of spiders and knowledge of two local species of Orbweavers commonly found in the Castlemaine region.



Left: Garden orbweaver in her web at night. Right: Golden orbweaver in her web by day with a tiny male approaching from above. Photos taken by: Dr Lynne Kelly

I adore spiders. I used to be an arachnophobe but knowledge cures an irrational fear, slowly at first. Then one day I watched an orbweaver spin her web from start to finish. That was the day I became a spider-obsessive. In the Mount Alexander Shire two varieties of orbweavers dominate – the large golden orbweavers who stay on their webs all day and the slightly smaller garden orbweavers that spin in the evening and scamper to hide in the foliage at dawn.

We have a few species of garden orbweavers. They are all in the Eriophora genus, distinguished by two prominent projections near the front of the abdomen. Garden orbweavers usually remove most of their web before dawn, re-absorbing the protein in the silk to use again. A single reinforced strand is left across the gap between bushes or trees in the hope that it will still be there the following evening. If that strand is broken, the spider will point her abdomen skyward and release a fine filament of silk. In even the slightest breeze, this silk will catch on foliage and she will rush across, back and forward, to reinforce the mainstay of her web. She will then drop to the ground and attach an anchor. She’ll rush up again to spin the radials and a spiral outwards. From the edge of her nearly complete web, she will then circle back towards the centre laying down the sticky spiral. Having worked tirelessly for nearly an hour, she will rest, head down, waiting for her prey.

Unlike the garden orbweavers, the huge golden orbweavers stay on the web all day, constantly repairing and reinforcing it. It is not the spider which is golden but the glow of the silk when it catches the sun. All the individuals I’ve seen locally are the Australian Golden Orbweaver (Nephila edulis). Discarded debris is left in the web above the spider to confuse the birds. Male garden orbweavers are only marginally smaller than their females but the males of the golden orbweavers are tiny by comparison [see above photo on right]. Although the males of most spider species will survive their sexual encounters, the Nephila males sacrifice themselves in their final act. Having produced a golden egg sac, the female will then die with the first frost.


For further reading, Lynne’s book, “Spiders: learning to love them” (Allen & Unwin, 2009) is an excellent resource for those interested in finding out more about these amazing creatures.

Monday, April 24, 2017

Identifying a spider from a photo

I get sent a lot of photos which people hope I can identify. I love getting them - I only wish I could do better on identifying. If they are common Australian spiders, I have a chance. With thousands of species identified in Australia alone and many more thousands yet to be described by science, my chances of recognising a spider from a photograph is small. When they come from other countries, I am often struggling to even know the family.

The problem is made worse because the photographs often don't show me what I need to know and the senders don't include the necessary information. I need to know where the spider was photographed - not only the location but whether it was associated with a web (really important), near houses, in a burrow, in dry bush or wet forest and so on. With the photos, most are blurry. As I need to see details like the hairs, that makes life difficult.

The eyes have it

But most useful of all are the eyes. Almost every spider photo is taken of its back. Spiders are often identified to family level from their eye pattern.

Today's photo included the eyes! Rushil Gupta sent me three photos of a spider to identify. The first gives you an idea of the entire photo, and the smallness of the spider in it. The next three are zoomed and cropped. [Click on images to see them better.]


The shape suggests a few possibilities. An arachnologist might be better able to leap to conclusions, but it is too blurred for me when I zoom on the spider:


This is clearer, and I am getting a good idea. But I still can't see what I need.

 

And the really useful one! I have the eye pattern. It has a large front pair of eyes ... jumping spider or wolf spider or lynx spider? The photo is clear enough to see the very strong spines on its legs, which indicates probably a lynx spider (family Oxyopidae). But it is the eye pattern which will clinch it - and Rushil's photo shows them.


A great site for the eye patterns of the common families is Bugguide:


This is found at http://bugguide.net/node/view/84423 (or click on the image). It shows the Lynx Spider family eye pattern to be:


Bingo! NOT! I jumped (pun intended as will be obvious soon) to conclusions too fast! Fortunately some experts jumped in - thank you Lizzy Lowe and Alan Henderson. The two little eyes under the large anterior median eyes aren't there!

I thought that I could see spines on the legs which is why I headed for lynx spiders. Clearly, I judged that wrong too.

Try again: This is the eye pattern of the jumping spiders, family Salticidae. So Rushil's spider is definitely a jumping spider.



From the bulges on the end of the pedipalps at the front, I would guess that he is a male wandering in search of a female. Now I need to hear back from Rushil to know what country the spider comes from. I can work out the size from the image!

UPDATE: Rushil tells me that he is in India. I'll wait for the experts to see if they can tell me more.

CONCLUSION: I am really good at loving spiders and observing my locals. I am no good at ID unless it is one of my locals - much as I would love to be and will keep trying.
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Thursday, January 26, 2017

Zoe's golden orb weavers

Zoe Stanford showed me a photo of a strangely coloured spider. The only possibility seems to be a golden orb weaver, Nephila edulis. (Click on images to see the detail.)


Zoe let me know of a new young golden orb weaver who had arrived. I asked her to take a series of photographs to show the way Nephila build up their set of debris above them on the web to act as a confusion for predators. This is the sequence she sent.





This is the final image of the spider, her web now full of junk.


Unfortunately, she has built her web in a place which had no protective foliage nearby. After a severe storm, Zoe found her spider dead in her web. So sad!

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