The one who thought about attacking April snarls when it sees Jack, getting its hackles up again. It can smell his blood, and they've all seen enough of Torchwood to know that humans holding things isn't a good thing for Weevils.

Jack can tell it's getting twitchy, so he fires the net gun at it, draping a heavily-weighted net over the alien in a matter of moments. The Weevil snarls again, struggling against the net.