What exactly are we looking at? I can see a black slug and a catterpillar.

And what looks like very black soil - what is it you consider a problem, Mick? Whatever the caterpillar is, it isn't vine weevil, chafer grub, cutworm or leatherjacket.

It looks like a cutworm to me, but probably ready to metamorphose.

Cutworm doesn't have those stripes, well at least, the ones we get here don't I believe.

Thanks for the replies.
The problem is the caterpillar or grub which I believe devastated the complete bed of geraniums by cutting holes in the leaves.
I have now cleared the bed and wish to replant with Wallflower
Q. should I treat the area before replanting and if so with what ?
Many thanks Mick

Not sure its necessary to treat with anything - what kind of holes were they? Neatly cut half circles round the leaf edges? Or generalised tatty holes all over? Or small indentations that turned into holes as the leaves grew larger, with some distortion?

Bamboo

Thanks for the reply have added photo of leaf damage.
Would like to prevent this happening to future plantings,

Mick

That does look like caterpillar damage of some sort - I don't recognise the caterpillar in the picture, and can't tell whether it has any legs, and how many pairs or quite where they're situated, nor can I tell whether there is a distinct head section. Deciding what it is is essential to deciding whether you need to use any treatment, though usually, the best method is picking them off the plants after dark by torchlight.

That catterpillar looks to have legs.

I personally like actterpillars due to the adult being a butterfly, but do know how pesky they can be due to the damage they cause.

I know a lot of people hate the catterpillars, but love the butterflies, except when they start laying their eggs on you favourite plants. LOL

Bamboo
Many thanks for your interest.
Mick