Lateral Science Inverted Three months in Australia Saturday 25th March 2006

The best hunting ground for one to discover Latrodectus hasselti is undoubtedly garden furniture. I had an hour to kill, and as my adrenaline levels were dropping, I decided to search for more of these exciting beast. These plantpots of Mary's looked good -

Note the lip of the green square one. That's exactly where you'd lift the thing. I could see the disordered web of a Redback from one side of the pot to the wood post. Tipping the pot revealed this monster -

You can see small dimples on the abdomen (opisthosoma) of the spider. Upon seeing my Redback photographs for the first time, I thought these dimples were spiracles. They aren't. Spiders and insects don't have active lungs; in order to breathe, they rely on gaseous diffusion through small openings in the exoskeleton - spiracles.

On the small scale of a spider, the average distance atmospheric oxygen molecules move through thermal energy is comparatively large. Fresh oxygen can therefore easily can travel down the spiraclar tubes by diffusion, there to power the animal's metabolism. Since this is a scale effect, it would not work with larger animals such as ourselves - this is why we have to expend muscular energy to pump air into our lungs. It's an example of why spiders and insects can't grow to immense size (remember the film "Them"?), although some use body pulsation to help diffusion.

In the Carboniferous era, dragonflys reached large size; up to a meter wingspan. They could do this because although the physical scalar constraints of diffusion were idendical to now, the level of oxygen in the atmosphere was around 20% higher then. The inefficient diffusion breathing for this size of animal was offset by this oxygen enrichment. However, even if the oxygen content were 100%, larger insects would be unlikely to evolve because of another scale effect. The exoskeleton of the animal would collapse through it's own weight.

Anyway, upon reading about spider anatomy, I found that the location of spiracles is on the lower side, next to the spinnerets. So, what are those dimples? I don't know. Perhaps they're external clues to some sort of chitinous bracing structure, from the exoskeleton to internal organs? If you know, please inform me.

Putting the camera on video, I started really annoying the spider with the stick. It calamitously ran up my arachnid probe and got within an inch or two of my hand... this bugger was fast! After throwing it to the ground whilst screaming "Whoa yer bastard!", I used the Olympus to make a Quicktime video of the Redback. Note my safety equipment (including sandals); nowt much happens at the end, as I was preoccupied with killing the brute.

 A scuttling spider (Quicktime vid, 8.6MB)

Lateral Science Home Page A plethora of unusual science & engineering

The Ernest Glitch Chronicles Victorian anarchic experimental science

The Young Man`s Book of Amusement Hundreds of entertaining experiments from 1854