Bicycle Mechanics - Dust cap needed for cartridge bearing freewheel hub?

I have a freewheel hub that uses cartridge bearings. There is no dust cap anywhere on the drive side of the hub, so that the outer surface of the cartridge bearing is exposed at all times. Is this usual, or should there be a dust cap to cover the bearing?

Thanks!

If it really is a freewheel (not casette) hub then the freewheel itself should cover and protect the drive side bearings. Also, are the bearing cartridges sealed? If not replacing them with sealed bearings would also help protect their internals.

Yes, it's a freewheel hub. I thought I'd ask because when the freewheel is screwed on, I can see the surface of the bearing through the small gap between the inner part of the freewheel and the lock nut. When the wheel is mounted, the dropouts on the frame protect that gap somewhat, but it's not too hard to imagine some mud or water splashing in there. They are indeed sealed cartridge-type bearings, so I'm not excessively worried about it, but I thought I'd ask. There certainly is enough space between the bearing and the freewheel for a dust cap to fit in there.

I wouldn't lose too much sleep over it. I ran a Specialized sealed bearing hub for thousands of miles minus a drive side dust cap and the bearing survived just fine. Maybe check loosescrews.com or your LBS if it bothers you that much. Depending on the brand/model, you might even be able to pick up the same hub cheap on ebay and just use the dust cap from that.