Dens

What gerbils need-  dens


Gerbils usually make their own nests and burrows to sleep in,  but you should still provide them with some sort of den (sometimes called a hidey-house or just house).  They may sleep in it,  but even if they don't,  they will appreciate the cover to dive under when something scares them.
If you can,  I would suggest a ceramic den.  If not,  wooden.  And though I've never used one,  I've also heard that coconut shells can be used,  as well as clay pots.
Plastic dens,  however,  should not be used.
For example,  this is a bad den.  This would probably be fine.
You can also make homemade dens.  This is what I often do.

Though they don't really count as dens,  some other "hideaways" you could give your gerbils are jars and mugs.