Is it obligatory to remove fly excrement from clothes if possible, otherwise not, given the hardship this causes, and what is the ruling on mosquito blood or blood that comes out of a person if injured?

What you find on your clothes from the traces of flies is excused due to the difficulty and hardship involved, and fly droppings do not defile clothes due to their small quantity and the widespread affliction with them. As for mosquito blood, some scholars consider it pure, while others deem it necessary to wash if it is abundant and widespread. As for blood coming from a wound, it is impure and must be washed from the garment and body, except for a small amount, which is excused according to most scholars.