They look like weevil grubs, they love living in compost under your plants and need to be destroyed. If you use non peat based compost they don't like it.

yep, vine weevil. They sit there and eat your plant's roots and eventually kill the plant. They then hatch into little beetles which eats the top of your plants.

you can buy a drench called Provado vine weevil killer, works a treat and it's probably better to use it as a prevention every year rather then when it's too late.

If these are all you have found then Provado would be expensive . Just squeeze them or drop them in bleach. Either way you need to be aware of the damage they do. Scottish did a brilliant blog on finding and disposing of these garden nasties a few weeks ago. I have just checked it was 9th October 2013 a blog titled "Don't be fooled by appearances"

The adults can swim in pure bleach without coming to any harm.
Do be careful with Provado, the active ingredient is a bee killer. It may soon be banned.

You need to use Provado as there are several generations in there. You cannot see the eggs. I suppose you could pour over boiling water but do not use that compost in the pot again, it should be OK for in the ground.

I have used Provado in the past and found it effective, but if it is a bee killer I will revert to stamping on the grubs and then treating the compost with boiling water. Sometimes I throw the compost away and sometimes I try some annuals in the pot after it has stood empty for a while. So far that has worked with no sign of recurrence in that pot.

Provado is a systemic insecticide and you only use it on pots. You do not use in the garden itself as you do not want to kill 'goodies' such as Ground Beetles etc. I cannot say if it is a Bee killer, but since Bees only take the nectar they must be absorbing a tiny amount, if any insecticide.