Bailey?

How long can beetles survive in mobile captivity?

Well, that depends entirely on the species of beetle.  Most common beetles, like the firefly or the dung beetle have lifespans of 3-8 weeks once they reach adulthood, whereas your less common Stag Beetle may have a lifetime of 12 months or more.  

That is the creepiest insect I've ever seen.  If I saw one of those in my house, I'd have a lifespan of less than 12 months...holy crap! 

So I guess, to answer your question, you can probably expect to keep a beetle alive in captivity for just a couple weeks, depending on how well you maintain the environment and provide enough food and water for beetle sustaining.  Why do you ask?

Well, there's a beetle in my car, and I want to know how long before the stupid thing dies.  I've had no luck trapping the thing, and one of its favorite hobbies seems to be flying past my ear when I'm driving, and there's just no reasoning with it.  I'm sure it will be able to survive for a while on food rations left from me eating the car (Dunkin Donuts bagels are really flaky when they're toasted), but there shouldn't be any standing water around, so maybe dehydration will be my friend here.