This is quite a large spider, its head and body alone are over 15mm (more than half an inch). What is it and what's it doing?

A

It is a Costa Rican spider, Ararchnida circusi, which traps insects by rolling over them over while balancing on its sticky ball of silk

B

It is Brachypelma Icelandi, found in Scotland, Scandanavia and Iceland, the so-called 'Snowball spider', which lauches a sticky ball of its silk at its victims

It is a British spider, Pisaura mirabilis, the Nursery web spider, which carries its babies around in a silk cocoon