Whilst horrid, Fly strike is surprisingly common, especially during warmer Summer months. The condition is very distressing, painful for your rabbit and can be fatal. So it really does need to be taken very seriously.
Hutch hygiene is paramount at all times, but especially in the warmer months. Higher risk bunnies are females that are unneutered, those that are overweight and so struggle to clean, those suffering with diarrhoea or urinary incontinence or those with dental problems where grooming is hindered.