[AuntB]

“I prefer “invaders” to illegal alien or undocumented alien. It’s what they are. They have crossed a border without permission. You don’t call vermin in your basement “undocumented pets” you call them invaders.”

Invaders AND squatters.

squat·ter (skwätr)

noun

3. a person who occupies illegally a vacant house, building, etc. (LIKE a COUNTRY!)

[raybbr]

Squatters only begins to describe what is going on...

in·vade   (ĭn-vād')   
v.   in·vad·ed, in·vad·ing, in·vades

v.   tr.

1. To enter by force in order to conquer or pillage.

2. To encroach or intrude on; violate: "The principal of the trusts could not be invaded without trustee approval" (Barbara Goldsmith).

3. To overrun as if by invading; infest: "About 1917 the shipworm invaded the harbor of San Francisco" (Rachel Carson).

4. To enter and permeate, especially harmfully.

v.   intr.
To make an invasion: "The X-rays showed that the cancer, which had invaded deeply into the chest cavity, was retreating" (Zach Rosen).

[Middle English, from Old French invader, from Latin invādere : in-, in; see in-² + vādere, to go.]
in·vad'er n.