Factors influencing molehill distribution in grassland: implications for controlling the damage caused by molehills

1. Moles are perceived as pests of farms, gardens, sports fields and nature reserves, mainly because they form molehills. The danger and inhumaneness of current methods of mole control (e.g. poisoning with strychnine or the u se of mole traps) means that non-lethal methods are sought. We examined the possibility of controlling molehill distribution by using management proce dures that alter the availability of earthworms, the principal food of mole s. 2. The abundance of molehills and earthworms was monitored over 2 years in an acid grassland where pesticide (with and without insecticides and mollus cicides), grazing (continuous grazing by rabbits vs. hay meadow), soil pH ( with and without lime), herbicide (with and without herb- and grass-specifi c herbicides) and fertilizer (N, P, K, Mg) treatments were imposed. 3, In the experimental area of 4608 m(2), a total of 1062 molehills formed, each with an average area of 0.14 m(2); a disturbance rate equivalent to 3 .2% of the soil surface over 2 years. Peak molehill production occurred in spring and autumn, with few molehills formed at other times of the year. 4. Molehill production in grazed areas was one-third that of hay meadows. H alf as many molehills formed in unlimed as limed plots. Significantly fewer molehills formed in areas where grass species were removed (herb-rich) tha n areas where no species were removed. Insecticide, molluscicide and fertil izer application had no significant effect on molehill production. 5. The treatments that had fewer molehills also had less earthworms, indica ting that molehill production was decreased, indirectly, through the treatm ents reducing food availability. 6. Reducing the number of molehills through management procedures that decr ease earthworm availability offers an alternative to lethal control of mole s. This could be achieved by allowing (or encouraging) soil pH to fall (e.g . withholding lime application; through the use of acidifying nitrogen-fert ilizers), by creating herb-rich swards or by preventing plant biomass from accumulating for long periods. These methods will be more applicable to gar dens, sports fields and nature reserves than to farms, where conflicts with normal farming practices would make them difficult to implement.