In reply to BusyLizzie:
> I suppose they might be travelling to a pond to do the frogspawn thing, but why not do that in one's regular pond?
Frogs don't live in ponds all year round. They are quite happy in damp areas, under foliage etc - that's where they find a lot of their food, like slugs and other invertebrates. They don't need standing (or running) water all the time. The ones that get squished are likely to have been trying to make their way to a pond (possibly the pond they originally grew up in as tadpoles) for spawning, having spent most of the year elsewhere.
For a few weeks now we've had two or three frogs hanging around in our garden pond, although most of year we hardly see any - one at most, but even then only occasionally. We now have three clumps of frogspawn in the pond, and the frogs appear to have pretty much b*ggered off. This is what they do. They (or others) will be back this time next year. Fortunately there are a lot of gardens backing on to each other round here, so the frogs don't have to risk road crossings (unless they're feeling really adventurous).
Post edited at 16:48