Dung beetles can tunnel into highly compacted soils from reclaimed mined sites in eMalahleni, South Africa

Dung beetles provide a multitude of ecosystem services that could be used to improve post-mining land use options. Highly compacted soils are a feature of reclaimed mine sites and may pose a significant challenge to tunnelling dung beetles. This study aimed to determine if dung beetles can tunnel into compacted soils, and how a range of soil penetration resistance may influence their tunnelling depth. Three beetle species were used: Onitis alexis (Klug, 1835), Digitonthophagus gazella (Fabricius, 1787) and Euoniticellus intermedius (Reiche, 1849). Five individuals of each species (at an approximately even sex ratio) were placed on 30 separate 1 Kg cattle dung pats where they were left to tunnel for 14 days. Dung pats were placed on the soil surface covering a range of penetration resistance levels between 100 kPa and 5000 kPa. D. gazella tunnels showed a negative correlation with increasing penetration resistance (p < 0.05; R2 = 0.65). While O. alexis tunnel depth showed no correlation with penetration resistance, E. intermedius increased tunnel depth with increasing penetration resistance (p < 0.05; R2 = 0.35). Although tunnelling depth was notably shallower than previously observed for E. intermedius, all three species could tunnel into the soil at the average penetration resistance of 3 193 kPa, and even beyond the maximum measurement limit of the penetrometer at 5 000 kPa.