Saturday, May 1, 2010

Waste not

It's always amusing when we see animals using objects around them in obvious ways. Ravens using twigs to poke at insects and sea otters using stones to break open clams illicit "aww" moments. Even more interesting is when the purpose isn't very clear.

Take for example the trashline spider, so called because these packrats of the arachnid world intentionally move towards the centre the debris trapped in web, arranging it vertically above and below the centre of the web.

While some of the debris is plant matter, insect carcasses are also retained to decorate the web (most other orb weavers simply stretch out their arms and cast the emptied ball of indigestible exoskeleton into the wind).

Larger orb weavers, in particular of the genus Argiope, also build this stabilimentum, it is thought, to protect the large webs from destruction by flying birds. This probably isn't as big a problem for these smaller Cyclosa Conica, whose orbs stretch no wider than 30 cm.

One of the fiercest predators of orb weavers are wasps, so it is thought that the garbage on the web might disguise the spider, who on its own is already fairly drab in colouration. Sort of like the millionaire who leaves his lawn untrimmed and drives a beater to distract from his wealth.

This is the first time I've seen a spider like this in the city...I've occasionally seen them in the forest, but the range of the genus is worldwide, as there were also about three who consistently made webs next to our mosquito netting in South Africa.