It appears to be a regional, AmE usage:
To grab on to an object, usually with a great deal of force. May also be used figuratively to indicate a strong attraction for an object or person. Ex: "When I saw her down the bar, I muckled right on to her." Origin: Downeast Maine.
(Online slang dictionary)
(US, dialectal) To latch onto something with the mouth.
- 1954, Elizabeth Ogilvie, The Dawning of the Day1, page 199: And how'd she get such a holt on you, Terence Campion, let alone the way she's muckled onto those Bennetts?