colour in the community garden

Because of Covid we can only have 6 people working in the garden at the same time. There is so much to see  if you look closely and many of our members are missing out. I was fascinated to see  what looked like laundry foam, bubbling away on a recently watered seed bed  - see extra.  Do you know what it is?  I couldn't find a slug or insect underneath.  This is about 3 inches long