Commensal spiders

I've sometimes wondered what happens to the really little insects that get stuck in spider webs. I'm talking about the ones too small to satisfy or even be noticed by the spider. Well I found out for myself one day when I started noticing commensal spiders.

'Commensal' is not the name of any one type of spider. Instead it's a term to describe the fact that they get their food from other spiders. These spiders are scavengers.

The spider in the photo above was crawling in a large orb web and the thing that made me notice it was that it looked mighty uncomfortable, like it didn't belong. For starters, it appeared to be working hard not to get caught in the web. Also the orb web was way too big for this little spider. It was fumbling along, picking at little trapped insects and remnants. You can see those food items in the photo.

It didn't take long to find the true owner of the web. That's it in the photo at the top right of this page.

Now I'm not saying that every web has commensal spiders helping themselves to leftovers. However, the bigger orb weavers are unlikely to be able to keep their webs free of the tiny insects that caught - insects too small for the big spiders to eat. The commensal spiders therefore perform a kind of service by keeping the webs clean, while filling themselves with plenty of free feeds along the way. I love it how things rarely get wasted in nature.

Do things always go so easily for the owner of the web? Of course not. Some spiders that hang around other spiders' webs do so because they like to eat the other spider, not its leftovers. Life can be pretty tough for spiders.

Here's another type of commensal spider. The little guy shown above was very small — it's leg span would have been about 2 cm. I spotted this fellow living in the web of giant Golden Orb Weaver spider in northern Queensland. To compare sizes, the Golden Orb Weaver in the centre of the web had a leg span of about 15 cm. I counted 18 tiny commensal spiders living on that web. They moved so slowly and carefully that the Golden Orb Weaver didn't seem the least bit interested in them.

And here's another spider from that Golden Orb Weaver's web. This one is feeding on a tiny insect.

• So, what's with this 'Nature Stuff' then?

Birds

• Indian Mynahs - pushy and invasive
• Noisy Miners - aggression in the suburbs
• Starlings - Another feral pest, or not?
• Australian White Ibis - conservation takes a twist
• Common water birds around Sydney
• Pacific Black Ducks
• Geese teeth - do birds have teeth?
• Rainbow Lorikeets - raucous and colourful
• Sulphur-crested Cockatoos - beautiful birds with an awful call
• Glossy Black Cockatoos - casuarinas' seed crackers
• Are they Crows or Ravens in Sydney?
• Black Swans - bird emblem of Western Australia
• Brush Turkeys - Cool birds, huge nests
• Darters - comfortable on land, in the air and water
• Australian Pelicans

Trees

• A few big Australian trees
• Unusual and beautiful Australian trees
• Why Australia's giant trees might never return

Reptiles

• Lizard bite - getting more than you bargained for

Insects and spiders

• One of the longest insects in the world (photos)
• Some common Australian orb-weaving spiders
• Hunstman Spiders
• Fear of Huntsman Spiders
• Golden Orb Weaver Spiders
• How many eyes do spiders have?
• How many eyes do insects have?
• How I catch spiders (to take them outside)
• The amazing net-casting spiders
• Commensal spiders - eating the leftovers
• What is a spider? No, seriously, what makes a spider a spider?
• Jumping spiders

Other stuff

• Book review: Back from the Brink
• So what's a feral species, really?
• Camouflaged critters - blending in to a scene near you
• Critters in the city
• Fire and the Australian bush
• Cute stuff - critters sure can look cute when they're little
• Wildlife photography - an unhelpful guide
• Feeding wild animals - is it a good idea?
• Photo Sales - I might have that Australian nature pic you're looking for
• In pursuit of the waterskiing duck (blog)