Hunting the Hunter (Part 1)

You would think that a spider as robust (and venomous) as a huntsman spider (Sparassidae) would be pretty safe from predatory and parasitic insects. But not so. This article is the first in a series on the insects which make a meal of large spiders.

A few years ago I witnessed a titanic struggle taking place on a window at the front of our house. A large spider hunting wasp (or ‘spider wasp’) was pulling a huntsman spider backwards up the window glass.

Wasp and huntsman

This spider is a female of the species Cryptocheilus bicolor of the order Pompilidae. These gorgeous black and orange wasps find a large spider and sting it to paralyse it.The female spider wasp doesn’t feed on the spider herself – the spider is food for her offspring.

Earlier that day I had seen our wasp digging a nest hole in the sand bank at the rear of our house. Many species of spider hunting wasps place their prey in a nest in the ground (one spider per cell) and lay a single egg on it. The hatching wasp grub feeds on the live but immobilised spider.

I saw her trying to fly with the spider but she could barely lift it off the ground – her wings were damaged as you can see from the image above. Dragging the spider was her best option and she was attempting a shortcut up over the house rather than going all the way around!

The glass was slippery and the spider was heavy and down down down she would slip – sometimes all the way to the ground. Each time she fell down she started the climb again. I have no idea why she insisted on going up glass rather than up the house bricks where she would have had more grip.

Eventually after about half an hour of this frustrating struggle she gave up and began hauling the spider around the house – a distance of about 50 meters. She accomplished the task of dragging the spider to her nest in just a few minutes. After about an hour she emerged from the nest and flew away. I assume she had laid her egg and had no more interest in the nest.

When spider wasps move around on the ground they move in a jerky ‘stop start’ manner and constantly flick their antennae and wings. The video below shows typical spider wasp behaviour (featuring a different individual to the one described above).

 

There are about 230 species of spider hunting wasps (Pompilidae) found in Australia. This is only one of the groups of insects which attack spiders – there are many more. The image below shows some insects from one such group. What are they? You’ll have to wait for the next ‘one minute bugs’!

insect

 

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Said the Spider to the Fly

“Will you walk into my parlour?” said the spider to the fly;
“’Tis the prettiest little parlour that ever you did spy.
The way into my parlour is up a winding stair,
And I have many pretty things to show when you are there.”
“O no, no,” said the little fly, “to ask me is in vain,
For who goes up your winding stair can ne’er come down again.”

This early 19th century poem by Mary Howitt paints a picture of a cunning spider trying to entice a fly into its web. In real life web-spinning spiders don’t try to inveigle flies, or any other form of insect, into their webs. Spider webs are spun across an area where prey is likely to fly or wander through, and (hopefully) blunder into (and get entangled in) the web. According to research, spiders collectively consume somewhere between 400 and 800 million tons of insects per year. Spider webs work pretty well then!

Orb web

Spider webs are made from spider silk which is produced from a number of silk glands located in the spider’s abdomen. The silk at this stage is a viscous liquid consisting of about 50% proteins and a mixture of other substances. The silk is extracted through special finger-like organs called spinnerets, which cause the protein molecules to align and form solid silk.

Modern web-spinning spiders have three pairs of spinnerets and each pair does a different job. The silk from the front spinnerets is used for attachment points, drag lines, and in the construction of the main frame threads of a web. The middle pair of spinnerets produce swathing silk used to wrap up prey and spin egg sacs. The rear spinnerets produce the gluey silk used in orb web construction.

Weight for weight, spider silk is up to 5 times stronger than steel of the same diameter. A silk fibre is approximately one micrometer in diameter which is about 80 times thinner than human hair. Male spiders often have fewer silk glands than female spiders – after all a male spider’s only purpose in life is to mate with females. Females need their full assortment of silk glands for web building, prey capture, and egg sac production.

Orb spider

Orb-weaving spiders, such as garden orb-weavers (Eriophora spp.), are very common in gardens, crops, vineyards and nurseries, and there are about 100 or so species scattered throughout Australia. These spiders usually construct a web in the evening and take it down at dawn. These orb webs are stretched across open spaces, which begs the question: How does a spider get her first thread across that open space?  She releases a long thread of silk which drifts in the breeze until it lands on something solid. If the attachment is to her liking she commences construction of the web proper, a process which takes about an hour. The web will be strong enough and flexible enough to stop a large insect flying into it at full speed. If the web was rigid rather than flexible it would break under such force. Garden orb-weaving spiders, like all other spiders are predators, meaning they are a beneficial presence in any garden, nursery, vineyard etc. The one in the image above has snared an Australian plague locust (Chortoicetes terminifera).

A web building spider may produce an egg sac containing hundreds of eggs. When those eggs hatch into spiderlings you might think the web would become overcrowded, but spiders have a clever solution for this potential problem. The spiderlings release a thread of silk which is picked up by the breeze and the spiderlings ride the air currents. This technique is known as ‘ballooning’ and spiderlings may be carried high up into the stratosphere and travel thousands of kilometres.

Sometimes there are mass ballooning events where many thousands of spiderlings descend on an area. There are numerous examples that will show up in a Google search. The media has a field day with these events, and they scare the living daylights out of arachnophobes everywhere. I guess nothing instills fear in arachnophobes more than the idea of venomous spiders raining down from the sky! Fear not – they are harmless baby spiders.

Orb weaving spider

My favourite web building spiders are the golden orb-weaving spiders (Nephila spp.) (pictured above). The ‘golden’ part of their common name refers to the colour of the web, not the colour of the spider itself. Their webs are huge, as much as a couple of meters across, permanent, and very strong. I know this from personal experience as I have blundered into them several times and basically bounced off! The webs are very complex, with a fine-meshed orb suspended in a maze of non-sticky barrier webs.

Female golden orb-weaving spiders sit head down in the middle of their orb waiting for prey to fly into the web and get stuck on its sticky threads. After she consumes the prey the remains are stacked into a string of debris in the centre of the orb. There is some debate about the purpose of this debris string – one of the theories is the debris alerts birds to the presence of the web so that they don’t fly into it and break it.

Finally, spiders shouldn’t be overlooked when it comes to insect pest management. I was amazed by the number of spiders I found in vineyards during my time with an Integrated Pest Management consultancy. In many cases spiders were the most numerous beneficial organism by far. Spiders are good!

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