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!