Ice-bores were worms that lived in the ice-packs of Andoria. They resembled Earth caterpillars and lived in large groups called "swarms".
Ice-bores generated heat through a chemical reaction, causing them to fall through the ice caves of Andoria. Andorian children often chased swarms for hours; however, it was always best to avoid this. Physical contact with an ice bore could result in third-degree burns, as Shran discovered when he stumbled into a large den as a child and received such burns over half his body. Aenar would sometimes collect ice-bores. (ENT: "The Aenar")
As the ice-bores seemed only to be able to travel downwards with the chemically generated heat, it seems likely that some other stage of their life cycle allows them to travel back up.
In the final draft script of "The Aenar", ice-bores were described as "pink-ish worms the size of a Humanforefinger." In omitted dialogue from the same script, Jonathan Archer speculated that ice-bores would be prized possessions of DoctorPhlox, if he obtained a few of them.