Crayfish occur naturally in most lakes & rivers in France.  The carp love to eat them & almost without exception where there’s large carp you’ll find crayfish too… they are an excellent source of protein which makes the carp grow very quickly.
Under normal circumstances they are not a problem to anglers but in the hot summer months when the water is warm even lakes without a crayfish problem can suddenly find they have some activity in the margins.  They will nibble away at your boilies and if the bait is soft enough they can completely remove them from the rig.  They can also cause the rigs to tangle with their incessant pulling & tugging.  But don’t despair you can get around them.
Here are some tactics you can employ;
  1. Use rock hard air dried boilies as hookbaits.  At least 48 hours drying so that they are so hard that you need a drill to get the hair through.
  2. Use plastic boilies as hookbaits.
  3. Use hemp and/or particle mix as a background feed. Don’t just use boilies
  4. Use plastic sweetcorn as your hookbait.  Fish 4 on a “stack” on your hair.
  5. Feed on a little and often basis & re-cast every couple of hours.  This allows you to re-bait & check that your rigs are not tangled or have been dragged into silkweed.
  6. Use protective mesh or shrink tube on hookbaits.
  7. Here’s some videos covering this subject.