How do you kill the skrewts climbing on buckbeak in year 3 Lego Harry Potter?

To kill the skrewts climbing on Buckbeak in year 3 of Lego Harry Potter, do the following:

1. Use Harry to cast Wingardium Leviosa to lift and throw an explosive barrel at the skrewts, causing them damage.

2. Shoot sparks at them using Hermione.

3. Continue casting Wingardium Leviosa and throwing explosive barrels until the skrewts are all defeated.