Duncan, whose most recent captaincy was earned at former club Cambuslang, said: “I’m very happy and very proud to be picked to captain my country and be in a position of power to unleash the dangerous back line that we have here.
“At stand-off you’ve got to be vocal and a leader on the pitch so there isn’t a lot to add to my role in that respect.
“We hear South Africa have gone for bulk and size, so we’ll be aiming to move them about a bit, and keep them moving.
“The young guys like Mark Bennett, Stuart Hogg and Glenn Bryce are all dangerous runners while throughout the team we have players that can beat a man one on one, so we need to use that to our advantage and not get caught up in an arm wrestle.”
Scotland U20
15 Stuart Hogg (Glasgow Warriors)
14 Sam Atkin (Edinburgh Accies)
13 Mark Bennett (Clermont Auvergne)
12 Danny Gilmour (Stirling County)
11 Glenn Bryce (Stirling County)
10 Duncan Weir CAPTAIN (Glasgow Warriors)
9 Sean Kennedy (Stirling County)
1 Alex Allan (Loughborough University)
2 David Cherry (Team Northumbria)
3 Colin Phillips (Edinburgh Rugby/Stewart's Melville)
4 Mitchell Todd (Nottingham)
5 Robert McAlpine (West of Scotland)
6 Jamie Swanson (Boroughmuir)
7 Alex Spence (Heriot's)
8 James Tyas (Bath)
Substitutes
16 Richard Ferguson (Melrose)
17 George Hunter (Glasgow Warriors/Glasgow Hawks)
18 Robin Hislop (Edinburgh Rugby/Boroughmuir)
19 Mitchell Eadie (Bristol)
20 Jamie Stevenson (Boroughmuir)
21 Kerr Gossman (Glasgow Warriors/Glasgow Hawks)
22 Hamish Watson (Leicester Tigers)