Stinging nest in the trees

Paid my dad a visit this afternoon, as I was meeting up with my sister to get my hair cut there. My dad looks after her son on a thursday so it's ideal. Arrived before my sister so I had an hours playtime in the garden with my nephew. We were admiring the apples on the tree when I suddenly noticed this, I said to my nephew who is 4 what do you think that is. A stinging nest was his reply and sure enough I then saw wasps making their way in. Now why didn't I know that .