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.

> From: 1954, Elizabeth Ogilvie, The Dawning of the Day‎, page 199:

> - *And how'd she get such a holt on you, Terence Campion, let alone the way she's muckled onto those Bennetts?*