I have an empty viv (read on!) which has been colonized by tiny spiders. They are neat, red legs (err, they are tiny, and this is the UK, so it's not Brachypelma emilia!). Every morning, the viv is festooned with webs they have spun during the night. They must be feeding on escaped flies from other vivs. Their fate will be sealed next week when the azureus go into this viv!