How do I get rid of ant nests in my polytunnel?

Ant nests in the polytunnel. What to do? Paul Rumgay, Co Wexford
This is a tough one. I once had to spend a couple of hours in a polytunnel where I was stung repeatedly by ants (I was helping out with a photo shoot and couldn’t escape), so I really sympathise. The painful stings of some ants aside, ants also feed on the sticky honeydew excreted by aphids, which they deliberately “farm”. The result is that aphids and other similar sap-sucking insects that produce honeydew such as mealy bugs and whitefly can become a real problem in a polytunnel where ants have taken up residence, as the latter protect them as important “livestock” that they rely on for a source of food. On the other hand, ants won’t directly harm your plants and are important ecosystem engineers, acting as natural predators of other destructive pests. They also help with seed dispersal and improving soil structure in a way that allows plants to more easily access nutrients and water.
But still, there’s no denying that a nest of them in a polytunnel isn’t desirable. The good news is that there are simple things that you can do to discourage them without resorting to the use of environmentally harmful and often ineffective insecticides. The first is to avoid the use of timber as retaining edges for raised beds, which they really like. The same goes for paving slabs, both of which provide the sort of dry, sheltered, concealed conditions that they favour as a location for their nests. Ants generally like a dry, sandy, warm soil and aren’t fond of moist, humus-rich soils, So the second tip is to keep your polytunnel well-irrigated and the ground generously mulched, using a good-quality organic mulch such as well-rotted farmyard manure or home-made garden compost.
Ants also dislike soil disturbance such as digging or forking the ground. Judging by the video you provided, this combination of mulching, watering and lightly forking over the soil in your polytunnel will also do a lot to boost its fertility and structure. Lastly, ants are reputed to dislike strong smells such as mint, lemon, vinegar, lavender and coffee, all of which many gardeners use as a means to deter them.