Acting Labour leader Harriet Harman said David Cameron "should remember he is talking about people, not insects" following his "swarms" comment.
She told the BBC the Prime Minister appeared to want to whip people up against the migrants.
Ms Harman also dismissed calls for the British Army to be sent in to sort out the problem.
I think it's a very worrying turn that he appears to be wanting to be divisive and set people against, whip people up, against the migrants in Calais when what he should have been doing, and should have been doing months ago and was warned to be doing, is to get the situation sorted out with the French.
Labour leadership hopeful Liz Kendall has defended the party's interim leader, Harriet Harman after others attacked her for endorsing key Tory benefit cuts.
Liz Kendall said it was essential that the party showed that it had changed if was to regain the trust of voters.
She said "People said to us 'We don't trust you on the money, we don't trust you on welfare reform.'
If we are going to oppose things we have to put something else in its place, because if we carry on making the same arguments we have done over the last five years we will get the same result.
"We have to put forward a different credible alternative and Harriet was absolutely right to say that."
Labour will not contest the Government's latest round of welfare cuts, including the lower household benefits cap and new limits on child tax credits, the party's acting leader has said.
Harriet Harman told the BBC that her party had to acknowledge that it lost the election because voters did not trust it "on the economy and on benefits".
Ms Harman said Labour would oppose some of the changes to tax credits, as well as the abolition of the child poverty targets, but that they wouldn't do "blanket opposition" because people don't want it.
Left-wing Labour leadership contender Jeremy Corbyn indicated he would not support Ms Harman's decision.
"If it is proposed that Labour MPs are being asked to vote for the government's plans to cut benefits to families I am not willing to vote for policies that will push more children in to poverty," he said.
David Cameron was told to "show more class" and answer the questions by Harriet Harman during a heated Prime Minister's Questions today.Read the full story ›
Harriet Harman has rejected the proposal that a new Labour leader should be put up for re-election in three years' time.
Some Labour MPs, including shadow education secretary Tristram Hunt, have suggested the next leader have a "test run" and seek re-election or re-endorsement before 2020.
But Harman, who is acting leader of the party, told The Observer whoever is elected should be allowed to get on with the job for the next five years.
Harman also announced a "truth and reconciliation" commission to discover why Labour lost the General Election.
The Labour Party wants to hold televised hustings in the parts of the country where it lost when it elects a new leader over the summer.
Interim leader Harriet Harman said she hoped to arrange "robust, tough, televised hustings which involve the public", and that she was speaking to broadcasters to make it happen.
She said: "Last time our hustings - in front of Labour members - were in cities where Labour won. We must have those hustings now in towns and suburbs where Labour lost.
"We have to go back and ask local people from those areas to be brutally honest about what they think of us and what they want from us."
Labour's interim leader Harriet Harman has said she wants to "let the public in" on the party's forthcoming leadership election.
Therefore, she has announced that anyone who pays the £3 fee to register as a Labour supporter will get a vote in the election.
She said: "Anyone – providing they are on the electoral register – can become a registered supporter, pay £3 and have a vote to decide our next leader."
She said the party had asked itself the wrong questions, deciding "who do we like" rather than "who does the country like" in previous contests.
Harriet Harman has admitted that the shock exit poll published at 10pm on election day was "a body blow none of us will ever forget".
Labour's interim leader made the remark in a speech on the party's forthcoming leadership contest.
Acting Leader of the Labour Party, Harriet Harman, paid tribute to Jim Murphy after he stood down as leader of the Scottish Labour party, saying he "has been a hugely important figure."
Jim has given so much to the Labour Party over the last twenty years. He, I know reluctantly, took the responsibility for leading Scottish Labour at the most difficult election they have ever faced. He did so with incredible energy, purpose and dignity.
As a cabinet minister and leader of his party in Scotland, Jim has been a hugely important figure in the Labour Party. He leaves with the best wishes and thanks of our movement.
It will now be for the Scottish Labour Party to choose its next leader.