Do you mean Darkling beetle?
They are a common vegetarian scavenger beetle, not really a pest unless they are munching on your lettuce. They live all over the place, all over the world.
Many people call them stink beetles- as they will spray a bad smell when molested.
http://www.insectlore.com/xlorepedia_stuff/darkling.html
Chickens might eat them, but they usually only come out at night.
They can carry some type of worms (tape worms I think) as the intermediate host, but so do most of the flies, beetles, and other bugs chickens might be inclined to eat. They have been suspected in transmission of some viruses (such as Marek's), but I think this is more because they walk around, and in and out of buildings/coops ect.
Marek's is spread by feather dander and is pretty much everywhere there are backyard chickens. Protect your flock from Marek's by vaccinating, and keeping your young birds away from older possible carriers and contaminated areas, not by killing off the native insect population.
I don't consider them a pest, unless I see one in my vegetable garden, then it just gets tossed over the fence. They serve a purpose- they eat dead and decaying vegetation.
Jess