I just had a look and it can cause stomach bleeding in other animals
'This tree contains phenolglycosides, salicortin and salicin. This last is an analgesic which led to the formulation of salicylic acid, aspirin.
It is often said that the bark contains aspirin but, in fact, it contains a substance which is far more likely to cause bleeding in the stomach than aspirin.'
Salix alba, white willow - THE POISON GARDEN website