Tenant Reported Ant Problem - Whose Fault?

[Daniel Alfandre]

The tenant says ants have come into the bathroom because there is no sealing/calk between the baseboards and the floor, which is where she says they are coming in.  Even though that area is not directly exposed to outside, as a general question, is it an opening to the house (hole, crack, etc.) that causes ants or is it food sources in the house that causes ants?

Further, what liabilities would an unsealed baseboard-to-floor cause me?  The place is 100% renovated and I missed this part of the renovation--there is shoe molding between the baseboards and floor in all the other rooms.

Thanks.