botfly, n. — Green’s Dictionary of Slang

botfly n.

[SE botfly, an insect of the genus Oestrus; its eggs produce the parasitical worm or maggot, the bot + bot v. (2)]

(Aus.)

1. an unpleasant, troublesome, interfering person.

1895

Coburg Leader (Vic.) 16 Nov. 4/2: K. O. B. of Coburg is going to kill the bot-fly for putting her in ‘They Say’.

2. (also fly) a scrounger.

1914		Sport (Adelaide) 12 June 4/3: They Say [...] [of a winning gambler] Ruggy Joe caught the bot through all the flies following him.
1941		Baker Popular Dict. Aus. Sl. 108: Hummer, poler and bot-fly are additional synonyms for a cadger.