Who did the jobs before illegals?
Probably the other immigrants who have been consistently coming into this country since the Industrial Revolution (albeit legally). Oh yeah, and before that, it was the slaves.
Not really. From 1925-1965 mass immigration was cutoff with an annual rate of about 250,000. Illegal immigration, though still a problem did not start to become this bad until the seventies and eighties but really exploded in the last decade.
The bottom line is American citizens did most of the work of the country and in fact in those areas not yet invaded continue to do so.