Green’s Dictionary of Slang

bugs and fleas n.

[rhy. sl.]

(US) the knees.

1935		A.J. Pollock Und. Speaks.
1944		Maurer & Baker ‘“Aus.” Rhyming Argot’ in AS XIX:3.
1950		Sun. Herald (Sydney) 5 Nov. 95/4: ‘Bugs and fleas’ [...] knees.