Soil Science

Spiders

Spiders are arachnids with four pairs of long legs. The body of a spider has two parts - the front part is formed from the head and thorax - the legs are attached to this - and the hind end is the softer abdomen. Spiders produce silk e.g. the webs of aerial dwellers or the linings of burrows of soil dwellers. Some make traps of silk at the entrance of burrows.

Spider hole among casuarina needles, Kangaroo Is, SA.
Spider hole among casuarina needles, Kangaroo Is, SA.
Spider hole among eucalyptus leaves in Gibraltar National Park, NSW.
Spider hole among eucalyptus leaves in Gibraltar National Park, NSW.
Soil-dwelling spider.
Soil-dwelling spider.

Soil-dwelling spiders live in soil crevices or dig burrows in the ground. All spiders are predatory, eating other soil animals, mostly the hard-bodied animals such as insects, woodlice and millipedes but they also eat worms. Some very large spiders in north QLD, Australia eat vertebrates such as lizards and frogs. Spiders have fangs which inject venom into their prey to subdue and kill it. Spider venom is a complicated mixture of chemical substances. In the funnel-web spider, the chemical in the venom that kills its prey is not the bit that's harmful to humans. It is another fraction of this chemical arsenal that kills us.

Some soil-dwelling spiders (e.g. wolf spiders) come out of their burrows to actively hunt at night. Others, such as the trap-door spider, use the ambush strategy. Trap-door and mouse spiders dig burrows in soil and line it with silk.The mouse spider can burrow quite deeply to 30 cm depth. They build a "door" to the burrow entrance, hinged on one side. The door may be formed from soil or a leaf. These doors are exceedingly well camoflaged and it is very difficult to detect them even when you know that they are there. Look away and back again and you've lost it! The spider hides in the burrow during the day but lurks near the slightly raised door at night to ambush any unsuspecting insect that wanders too close to its den.

Wolf spider close up.
Wolf spider close up.

Looking for spiders: The majority of spiders are nocturnal. You may think this makes them hard to find but sometimes it can make the job easier. At night, get a nice bright torch with a fairly focussed beam. Turn on the torch and shine it in front of you with the rear end of the torch just below the height of your eyes. Scan the ground. This is where you will find most of the hunters such as wolfspiders. The eyes of the spiders on the ground will reflect back the torch light and will appear like little bluegreen pin pricks.

Wasps and Spiders: The tables are turned here as the predator becomes the prey. Some spiders are prey to spider wasps. In the photo you can see the orange and black wasp dragging a large subdued huntsman spider along the ground. The female wasp has already dug a hole in soft soil and then found the huntsman spider either behind bark or under rocks and logs. The wasp stings and paralyses the spider, drags it back to the hole and lays an egg on the spider. The wasp larva hatches out and starts to eat the still-living spider. Nature is not always benign.

Spider wasp dragging paralysed huntsman spider back to hole in soil.
Spider wasp dragging paralysed huntsman spider back to hole in soil.

IMPORTANT
Do not attempt to catch spiders.
Leave them where you found them.
Just look and keep your distance.
Remember many Australian spiders are extremely poisonous.

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