Nursery web spider (Pisaura mirabilis)

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

C

The Nursery web spider uses its fangs to carry its babies around in a silk cocoon. When when they are old enough, it builds a silk tent for them to live in till the spiderlings are big enough to survive on their own