Looks silly at first glance, but I think it is a very interesting question. Asking Google I found a lot of "they die", but no good research about the cause (admittedly, I only spend a few minutes). Only one other - still open - question on Quora: https://www.quora.com/Has-anyone-tracked-the-cause-of-death-... -- The only answer says it has not been studied thoroughly, but it is from someone whose professional and job title ("Biomedical gerontologist, Chief Science Officer of SENS Foundation") sound like he would/should know.

I think it is implied that the cause of death is ageing? What else would it be (lab fruit flies don't have predators)?

I found a hint here: http://genomics.senescence.info/species/entry.php?species=Dr...

> Little is known about causes of death in old fruit flies but cardiac ageing has been reported [0981].

That sentence indicates that the question is not very well researched?

If that is true I find it amazing that there are ageing studies, shouldn't their own cause of death be well-known?

To @gweinberg, if you are reading this, what do you base this on? You wrote

> few of them die from age related causes

Broken hearts.

Bad autopilot implementations.