Most arable fields will have a grass margin of some description around the edges of the field. If there are hedges or watercourses then a minimum of 2m margin must be left from the centreline of the hedge or the top of the bank of a watercourse or ditch, to meet cross compliance rules. These strips of habitat are an important feature for biodiversity, particularly in an all-arable environment, providing shelter and nesting sites for a range of insects, birds and mammals, and they create wildlife corridors for species to move along. The wider the margin, the bigger the benefit. As well as helping to boost biodiversity, grass margins can, given the right conditions, provide a suitable habitat for predatory insects and spiders that can be of economic benefit to your arable business, and help form part of an integrated pest management approach. However, many grass margins are poor quality, with a lack of flowering species for pollinators or tussocky grasses to provide the over-wintering habitat required for many beneficial insects. In large arable fields often grass margins are too far apart to allow predatory insects to travel to the centre of the crop, reducing their benefit. This is where establishing a beetlebank can be effective.
Beetlebanks are essentially a field margin through the centre of the field, without a hedge or watercourse within them. They are formed by creating a slight ridge or mound and allowing to grow with tall tussocky grasses, but they can also be sown with nectar rich flowering plants to create a more diverse habitat suitable for pollinating insects. Generally, beetlebanks are only required in large fields (>20ha) where insects cannot walk across the entire field, though a good beetlebank will be a valuable habitat to boost biodiversity no matter the field size.
To establish a new beetlebank, plough so that a ridge is formed approximately 40-50cm high and 2m wide by two directional ploughing. The beetlebank should be parallel with tramlines, leaving enough room at each end to turn a sprayer and for normal farming operations to continue unhindered. The ridge should be sown with tussocky grass species such as cocksfoot, timothy, and red fescue. These grass species form an ideal wintering habitat for predatory insects such as spiders, beetles, hoverflies, and parasitic wasps. The grasses can be established in late summer and may need cut several times in the first year to allow the grasses to tiller and provide good coverage. It may be necessary to carry out some knapsack spaying of weeds, such as thistles, to prevent them from dominating as the beetlebank becomes established. Once established, it is best not to cut them at all to allow the tussocks to form and provide the desired habitat.
As well as providing a habitat for valuable predatory insects and spiders, beetlebanks can also provide nesting sites for ground nesting birds such as skylark, and shelter for mammals such as mice, voles and shrews, which in turn will benefit birds like barn owls. Beetlebanks could also be established along a slope in a field to help reduce soil erosion and run-off.
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