Harvester ants (Messor galla Forel) would defy various control strategies. Two field experiments were conducted to evaluate the effects of spent engine-oil and other naturebased materials on their emergence in Maiduguri, Borno State of Nigeria. The evaluated treatments are spot applications of spent engine-oil and some natural materials in experiment 1 and individual and equal mixture of pure neem seed kernel oil and spent engine-oil in experiment 2. Spot application of permethrin served as positive control. Experiment 1 results showed no significant difference (p>0.05) between permethrin and spent engine-oil (which was the most effective treatment). While neem seed oil was significantly (p<0.01) more effective than the untreated control, the result on the 28 th day after application showed no significant difference (p>0.05) in the population index of ants that emerged from nests treated with aqueous neem seed extract, salt/potash solution and extract of Eugenia aromatica fruit from those of the untreated control. Experiment 2 result showed no significant difference (p<0.05) between Permethrin, spent engine-oil, neem seed kernel oil and an equal mixture by volume of pure neem seed kernel oil and spent engineoil in suppressing the emergence of the ants. These were, however, significantly different (p>0.05) from the untreated control. While the result shows no significant difference between the insecticidal treatments, it was observed that equal mixture of spent engine-oil and neem seed kernel oil was the most effective, followed by spent engine-oil, permethrin and neem seed kernel oil in that order.