There is no need for immediate panic though, an international team of astronomers says.
It's not set to collide with the Milky Way for about four billion years.
The team has studied globular star clusters and believes they show faint traces of smaller galaxies that Andromeda has devoured within the last few billion years.
Co-leader ANU researcher Dougal Mackey says they also found very faint traces of small galaxies that Andromeda probably consumed even earlier, perhaps 10 billion years before it was first forming.
"The Milky Way is on a collision course with Andromeda in about four billion years," Dr Mackey said.
"So knowing what kind of a monster our galaxy is up against is useful in finding out the Milky Way's ultimate fate."
He says by tracing the faint remains they have been able to recreate the way Andromeda drew them in and enveloped them at the different times.
Co-leader Professor Geraint Lewis from the Sydney Institute for Astronomy and University of Sydney School of Physics said their discovery presented new mysteries.
They found bouts of galactic feeding coming from completely different directions.
"This is very weird and suggests that the extragalactic meals are fed from what's known as the 'cosmic web' of matter that threads the universe," Prof Geraint said.
"We're going to have to think quite hard to unravel what this is telling us."
The study, published in Nature, analyzed data from the Pan-Andromeda Archaeological Survey, known as PAndAS.
The team involved institutions from Australia, New Zealand, the United Kingdom, Netherlands, Canada, France and Germany.
© AAP 2019