What's in a word?

I suppose it's natural for those who want to have a pop at the Prime Minister to scrutinise his every word in the hope of finding something to criticise, but was he wrong to refer to the migrants in Calais trying to get over here as a "swarm"?  Well, it's true that the expression is most often used to refer to insects, but my dictionary also defines the word to mean "an aggregation of persons or animals, especially when in turmoil or moving in mass", and that, to me, pretty well describes what is going on over there.