Well, yes, crud can get in there, and you should watch for it. A lot depends on where you will be flying. Most fields I've flown from were either grass or grass with a paved portion, not a lot of loose dust or dirt to get sucked in to the engine. If you do a lot of lawn mowing with the prop, you can get clippings in the carb, but I've never heard of that being a problem.

I always close the throttle on my engines after flying, and check in the intake before starting for the day in case some crud got in there in transport or storage. It's easily washed out with a bit of fuel and/or a q-tip. (I keep q-tips in the field box for this reason)

Then there was the day we were flying right after the geese left the field. Goose s#!& + prop = mess. But that's another story, I'm just glad it wasn't my plane that ate the goose leavings.

And I did see a picture of a bee that got sucked in to an intake and stop the engine once. Didn't hurt the engine. The bee wasn't so lucky.

Sooner or later, you'll plant the engine. When you do that, you can be pretty sure there will be dirt in the carb. However, it's easily washed out with fuel, wd-40, or any number of other cleaners. You don't want to turn the crankshaft if you suspect stuff is in the engine. I'm not going to go in to a full "how to tear down and really clean out an engine" here, but it's not hard.

You can buy air filters that fit over the carb. But to be honest, I've never seen anyone use one, it really is pretty rare to actually get anything in there. Also, too much of a filter will reduce the engine's power as airflow in to these little engines can be rather critical.