Tuesday, 30 January 2007

#4 A Spider and its Offspring

Have you ever stumbled into a huge spider's web amongst the shrubbery or behind the shed and had to fight your way out of the clutches of the silk?

This common garden beauty is the likely owner of that web

As its common name suggests, the Golden Orb-weaver Spider, Nephila edulis, spins an orb web of golden silk. The extensive semi-permanent web is remarkably strong and makes a formidable sight when several spiders overlap webs creating a dense and almost impassable barrier. Walking into a mass of Golden Orb Spider webs either in daylight or the dark is enough to make even the toughest Aussie bloke squeal like a girl (now, correct me if I'm wrong please) .

A luckless cicada is no match for the strength of a Golden Orb-weaver's web

But the Golden Orb really is a gentle giant. Despite a mature female's body size of up to 3cms (excluding legs), these spiders are not aggressive and will dart to the top of the web if disturbed. Being diurnal, they spend the day in their web protected from birds and wasps by a network of subsidiary threads safeguarding the main web.

A spider must shed it's external skeleton in order to grow. This is a complex process whereby enzymes dissolve the layer between the skin and the rest of the body, and a new skin begins to form below the old one. The nerves stay connected to the sensory organs on her old skin so that she is not deprived of essential signals from the sensory organs on her legs.

The skin starts tearing at her jaws and the crack enlarges to the abdomen. When the skin has become completely loose the spider falls out of her old skin.

A Golden Orb limp from having just moulted hanging below her old skin with a male lurking above

Spiders can often be seen with one or more missing legs, but after moulting these lost legs regenerate. Isn't nature amazing!


Spider sex is a lot more intriguing than one might initially imagine! While the female Golden Orb-weaver Spider's body measures over 20mm, the male is a mere 5mm. If you take into account the female's fettish to feast on her suitor once he's served his purpose, then the male appears to be courting danger. But like most males a courting, he can be quite resourceful.

The male Golden Orb lurks on the perimeter of the female's web feeding on left-overs, waiting for a mating opportunity. He then begins his mating sequence after the female has caught prey, therefore limiting the likelihood of becoming the female's next meal.

Spiders have a pair of feelers (or more correctly, pedipalps, or palps) located on the jaw. The male's palps have a bulb on the end that is used to hold sperm to be injected into the female. First, the male must eject semen from his genital opening under the abdomen then suck it up into his palps ready for insertion into the female.

In the image below you can see the swollen bulb on the tiny male's palps. Compare the shape of the male's palps to the female's palps in the third picture. Also in the image below, the male is hovering at the female's genital opening while she is limp from moulting and looks suspiciously like he is taking advantage of the incapacited female. Notice also, the screw-like extension on the end of the palp that is used to gain access to the female genital opening.

A male possibly attempting to mate with an incapacitated female

The female will wrap her eggs in a sac of golden silk

After several months the Golden Orb hatchlings will emerge from the egg sac and balloon away on the breeze. I first noticed the spiderlings in the image below emerging in June from an egg sac that was deposited in March. The tiny Golden Orb-weavers re-entered the sac and emerged again in August. They eventually disappeared in September after a total of six months.

Golden Orb hatchlings are less than 1mm in diameter

The hatchlings then must endure the hazards of predators and weather. Hopefully some will survive to grow and repeat the process. Since observing and researching these awesome spiders hanging in their shiny webs in my backyard, I have come to respect them and their complex lives.

A young female Golden Orb-weaver displays beautiful colouration that will fade to a silky light brown as it matures

Golden Orb weavers have relatively poor eyesight as they do not rely heavily on sight for catching prey. They are reluctant to bite and are not considered very toxic.

Perhaps next time you see one of these impressive spiders hanging overhead you will also appreciate their place in the environment - they're not as scary as they might first appear.


Esperance Blog said...

Very impressive Gaye, you have obviously spent a very long time getting to know them. Great close-ups too.

As Golden Orb Spiders are usually found on their webs during the day, any ideas why the birds don't prey on them?

Gaye from the Hunter said...

Hello Jack, this is something that has intrigued me. Upon taking notice of details of their webs, I presume the haphazard arrangement of threads forming a maze in front of or beside the main orb web deters predators.


Anonymous said...

Nice pics Gaye,

I remember these spiders in a gum tree in our front garden in Adelaide. I saw a Purple Crowned Lorikeet get caught in web and was stuck for a good 10 or 15 seconds before falling to the ground. Took the bird a little while to remove enough of the web before it could fly away.

Can't wait to get a decent camera and get stuck into taking a few pics. What camera do you use and what can you recommend. I'll only have $300-$400 to spend and was wondering whether second-hand might be an option?


Gaye from the Hunter said...

hi Peter, that's an interesting observation re: the bird temporarily caught in the spider's web. Thank you for sharing that.

The 2 cameras that I use are noted on the right-hand side of my blog home page. Unfortunately I am not experienced enough to recommend a camera, but I personally would steer clear of a second-hand digital camera. There are some economical and efficient digital cameras on the market.

For the wildlife and invertebrates etc that I photograph around my yard, I mostly use my point-and-shoot camera because it is compact and easy to cart around. I put it in my handbag and it goes everywhere with me. It is only 3.2 megapixels but produces an adequate image.

Good luck with your purchase. It will change your life!


elfram said...

I appreciate your tenacity in taking those excellent images, and also in checking out the facts so you can assemble it all into an interesting piece of nature writing. Keep up the good work!

I'm a bit too distracted in recovering from surgery to write for my own blog but I will persevere. You certainly set a good example.

Gaye from the Hunter said...

hi Bill, and thank you for your encouragement.

As your health improves you should once again have the energy to persue your computer interests. That's something to look forward to, meanwhile, follow doctors' instructions for a smooth recovery :)


Anonymous said...

Hi Gaye
Great addition to your blog. All the information is again very informative and interesting at the same time.
As always your photos are GREAT!
Look forward to your next installment.

Gaye from the Hunter said...

hi Maria, it's great to know that there are women who appreciate the beauty of a spider. Thanks.

MIssAnthropy said...

"Perhaps next time you see one of these impressive spiders hanging overhead you will also appreciate their place in the environment - they're not as scary as they might first appear."

Hi hv :)

I answered your excellent advice over at scribbly, but - just in case you have not seen it there:

One Golden Orb, who made her home on my verandah, owes her survival there not least to you !:)

Your blog is stunning - !! I have dropped in quite a few times - as a lurker. Thanks for your great work.

Gaye from the Hunter said...

Hello MissAnthropy,

I'm pleased you were able to relocate your Golden Orb Spider decorating your verandah. They do look scary, but as you found, not aggressive at all.

Thank you for your comments. It's great to know that my nature observations are being enjoyed.


whatihavelearned said...

hello gaye,

we too, love your blog.
my son is researching golden orbs for school and your info is the most kid friendly we have come across. do you mind i use some of the info for the project?

cords and ollys
(lower hunter)

Gaye from the Hunter said...

hi cords and ollys,

I am pleased that your son has found my nature blog suitable for his age group. One of my aims with my blog was to make it student-friendly.

Please feel free to use my information and pictures for school projects.

I had a Golden Orb hatch in my garden this week, so you may be lucky to find a hatch to observe.

Thank you for leaving a comment, as it is great to know that children are finding my nature entries of interest and use.


EricG said...

Great shots Gaye! I love these little guys. The main reasons birds don't attempt to have these guys as lunch is a point you touched on - the fact the web is so large, intricate and strong, deters most birds. Also, I have seen Orb spider's take down birds and have THEM for lunch, so the word's probably gotten around. Those birds like to talk ;)

Gaye said...

Hello Eric,

thank you for leaving a comment on my blog. I haven't seen many Orb Spiders throughout summer - there's no garden where I am at the moment, so there's little habitat. But I have a leaf-curling spider of some sort hanging off the guttering near the front door - been there for a couple of months now, so that's some consolation. I've had to shift it to one side a couple of times so I can get in the door :)