Tiger Moth

Please could someone tell me - what on earth was happening to this moth??? I saw something almost the moth's length dangling from the back of it. By the time I'd come back with my camera, the 'dangling bit' had almost completely disappeared into the moth (see 1st & 2nd shots). The 3rd shot was a matter of seconds later. The 4th was taken about a minute later.
Length of moth approx. 3 cm (1.2 inches).