It really depends on the nation in question. For example, the announcement of war in Russia was greeted by anti-German rioting in 1914. In Moscow, there were riots in the streets and while at first the police tried to stop them, they gave up their attempts. Instead, they found all the German nationals in the city and evicted them, most likely saving their lives. The distrust of the Germans was enormous at the time. This posed problems for the Russian royal family too because the Tsar had married a German. Germans who remained behind lied about their origin - the source I'm using is a biography of Frederick Bruce Thomas, who had a German wife who at this point claimed Swedish ancestry.

This was in Moscow though - the Russian heartland. In the South, at Odessa, it was different. Odessa was a port city, with huge amounts of trade running through it, and consequently had a massively diverse population. It was filled with practically every nationality from Europe, and they were able to live there comfortably until at least 1916. In the case of Russia, I suspect this is because Odessa and Moscow had vastly different histories and cultures based on location.

Source: The Black Russian, Vladimir Alexandrov.