How do aphids get in?

[COMPOST CORNER]

My plants that have been kept in the house so far have today been found covered in aphids.
How on earth do they get there?
Could they have overwintered on my Chilli plant, and if so, why have they just appeared now?

[Two_Sheds]

Overwintered eggs hatch when the weather warms up, then the whole cycle starts again