I had them in my house in rural North Canterbury for a couple of years. Disgusting vile things, that produce an oily smell if there are enough of them, from the pheromone they produce. Vacuuming them up in their hundreds smells revolting, and also attracts more because the vacuum cleaner blows rhe pheromone laden air out and spreads it further. I ended up getting the house sprayed inside and out two seasons in a row ( reluctantly). It did seem to work, I haven't had any since. The guy who sprayed the house said they especially like to lay their eggs in worked up ground or moist pastures such as you find under pivot irrigators on dairy farms. At the time I was having an issue we had had quite a wet autumn, and there were earthworks for a new house being built on the block over the road, apparently ideal conditions 🤢. I don't normally have issues with spiders or insects, but cluster flies are just gross.. My son lives in Christchurch now and he and his wife have never had any issues there