Mostly they are looking for food, which is usually some sort of wood.  Sometimes they've come to your house chasing water to drink and then look around for closer food.

All pests, like us essentially seek the same basic things: food, shelter and water to drink.  Without good supplies of these they can't thrive.

The process of baiting for termites is highly variable. 

Sometimes much of the time is spent getting them into the baits.  Sometimes they're in by day two.

Some bait toxins take several weeks or months to noticeably affect the colony.  This is especially true of the hormonal approaches.  Some toxins will usually kill off a colony within two to three weeks of the first feeding.

Baiting for termites has a long history.  I first used it in 1979 to survey a park, but others had used baiting way before then.  Basically, a bait is something that termites will happily eat.  Often it is placed in a fancy (=expensive) container.  When the termites are feeding on the bait you (i) know they are there, (ii) can identify them and (iii)  you can exploit them.  The original bait box method had the termites collected and dusted with toxin before being allowed to sulk home.  Other methods

Very few termites are likely to be interested in eating the straw bales themselves.  Lots of subterranean termites will happily travel through the bales to reach unprotected framing timbers (such as door frames and window lintels). 

You won't sit the bales right on the soil anyway (moisture hazard) so all it takes is some attention to design to put a termite barrier in the foundation, just as you would with any other block house design.

If you've already built without barriers, find a well-skilled termite manager to inspect and advise.

Orange oil is the name given to extracts from the peel of citrus.  Mostly this is near pure d-limonene.  It is a general solvent.  You have probably used it in bathroom or hand cleaners.  It kills insects.  I used it as the recommended cleanup solvent for the Blockaid non-toxic termite barrier as it was much less of an OH&S risk than mineral turpentine.

They might.  Subterranean termites, of most types, will travel at lest 50 metres through the soil to exploit good food.  Termites flying from colonies can sometimes spread a thousand metres.  If your house is well maintained and has a termite management plan, the risk can be reduced to something quite acceptable (but never totally removed).  Apart from known colonies of major pests very close to a building, there is usually little to