Parktown prawn, n. — Green’s Dictionary of Slang

Parktown prawn n.

[Parktown, an upper-class Johannesburg suburb + SE prawn; the cricket, which grows to 7cm (2¾in), can seem to resemble an outsize prawn]

(S.Afr.) the king cricket (Libanasidus vittatus).

1984		Fair Lady 30 May 176: What about the dreaded Parktown prawn that stalks Jo’burg’s trendy suburbs? [DSAE].
1996		Davis & Fuchs Theatre and Change In S. Afr. 177: The ‘Parktown Prawn’ is a large and particularly ugly looking type of cockroach which terrorises households in Johannesburg.
2005		W.H. Robinson Hbk of Urban Insects and Arachnids 351: This species is called the Parktown prawn, because adults accidentally occur in swimming pools in the (Parkstown) suburbs of Johannesburg.