Could it be stone martens? We had stone martens who used to go mad in the garden at night and literally crash their way through the plants crushing everything. They are a real pest here and particularly like to chew cables and rubber fittings under car bonnets, in fact car insurance covers marten damage.
Well, it might not harm anything, but could certainly attract ants! Just my thoughts, if it was me wouldn't do it (except plain mineral water, use that on my houseplants occasionally).
35°C in the shade expected by lunchtime, 32 right now (10am) (wipe sweaty brow smiley!).
Are you puttung cooked food into the compost heap? This will attract rats!
It's not called catnip for nothing! If you don't like "vermin", don't plant catnip!
These are definitely ladybird eggs:
If you google "insect eggs" or insect larvae" and select images, you will find lots of sites.
Check on Amazon, big selection, much cheaper than waterbuttsdirect!