Illegal Migrants and Safety in Numbers

A recent trip to L.A. reminded me of the decision making process that illegal migrants go through (go figure). Decisions like where would they choose to locate once crossing the border, jumping off ship, sneaking out of the airport etc. Why do illegal migrants flock where most illegal migrants like them are massed (coincidentally most legal migrants of the same ethinicity as the illegal migrants are also in these areas)? They choose to locate in Florida, New York, California, Texas, etc. Aren't they afraid that a dragnet for illegal migrants would easily catch them at these locations?

Sociologists would probably claim that they choose to live in these enclaves because the cost of adjusting to a newer environment, setting up social networks etc is lower. But I think, the relevant cost for the illegal migrant is the cost of having to go back to a place he already decided to leave. If social networks were so important he wouldn't have scaled the fence in the first place.

They choose to locate in these areas because the probability of getting caught is lower. It's safety in numbers. The key factor is that there is a cost for the authorities to catch one illegal migrant, and that this is at least a constant per unit cost, it becomes an increasing cost if the catcher has to sort through a hay. In L.A. it's not like looking for a needle in a haystack, it's worse, it's looking for a hay in haystack.