Some fans think that Ferb's biological mother is an alien, making Ferb a half-alien. Lala Stellune suggested that Ferb's biological mother had a child with Lawrence for world peace.
- Lawrence sings Alien Heart, possibly referring Ferb's biological mother.
- Ferb's odd traits:
- Green hair
- Oddly shaped eyes
- Advanced technology
- Weird appearance in "Mommy Can You Hear Me?"
- Speaks Martian ("Unfair Science Fair Redux (Another Story)")
- A theory from TV Tropes suggests that Ferb's biological mother is French, explaining why Ferb celebrates Bastille's Day and speaks French in "Run Away Runway". Another theory suggests that she has a French-American dual citizenship.