The Warriors are rooted to the bottom of the Guinness Premiership table after losing all seven league matches so far.
Larder, 61, who was released by England following last season's disappointing Six Nations campaign, will join the Worcester coaching staff until the end of February.
Director of rugby John Brain indicated Larder's brief at Sixways will be wider than just defence.
Brain said: "I've been speaking to Phil for the past couple of weeks and he's going to be doing some work with us.
"Obviously, we have to make sure that our back line attack and team attack is more cohesive than it has been."
Larder is expected to start his hands-on coaching with Worcester after Friday night's vital Guinness Premiership game at fellow strugglers Harlequins.
The former Great Britain rugby league coach moved to union in 1997 after being approached by Sir Clive Woodward to join the England set-up.
Larder played a key role in the 2003 World Cup victory and was a member of Woodward's Lions coaching staff last year.