Harvester ants (Messor galla Forel) are field and store insect pests that may cause extensive damages to crop production. Two field experiments were conducted to evaluate the effects of spent engine oil and other nature-based materials on the emergence of harvester ants in Maiduguri, Borno State of Nigeria. The treatments evaluated were spot application of spent engine oil and some natural materials, or the application of individual and equal mixture of pure neem seed kernel oil and spent engine oil. Spot application of permethrin served as control. There was no significant difference between permethrin and spent engine oil regarding their effects on the population index of the harvester ants (P > 0.05). Neem seed oil was significantly more effective than the untreated control (P < 0.05). However, after 4 weeks application, aqueous neem seed extract, salt/potash solution, and extract of Eugenia aromatic fruit showed no significant difference in the population index of ants that emerged from treated nests in comparison with the untreated control (P > 0.05). No significant difference was observed between permethrin, spent engine oil, neem seed kernel oil, and equal mixture by volume of pure neem seed kernel oil and spent engine oil in controlling the emergence of the ants (P < 0.05). These were however, significantly different from the untreated control (P > 0.05). Equal mixture of spent engine oil and neem seed kernel oil was most effective, followed by spent engine oil, permethrin, and neem seed kernel oil. This study has shown probably for the first time, the potential of spent engine oil and neem seed kernel oil individually or in combination as a cheaper, technically effective, and conservation minded alternative to synthetic pesticide in harvester ant management.