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The occurrence of entomopathogenic nematodes (EPNs) in arable soil samples from Nigeria was investigated using Baermann extraction tray and insect-bait (White’s trap) techniques. Isolates were tested for infectivity using the larvae of Galleria mellonella (greater moth) and Tenebrio molitor (mealworm). The study revealed a new species of Heterorhabditis (MT371593) in soil samples that were randomly collected from an arable farmland cultivated with cassava TMS-30572 at the Teaching and Research Farm of Landmark University, Nigeria. Amplification of the internal transcribed spacer region (ITS) of the ribosomal DNA produced a nucleotide sequence of 933 base pairs (bp). A BLASTN search of GenBank showed that the sequence of the Nigerian isolate is identical at 99% similarity to that of Heterorhabditis sp. from Thailand. Infectivity test of the isolate showed 100% mortality against T. molitor larvae within 48 h of exposure while only 80% mortality was recorded for G. mellonella after 1 week of exposure. This is the first account of Heterorhabditis sp. in Nigeria. The varying degrees of infectivity against mealworm and greater moth observed in this study proved that the Nigerian isolate of Heterorhabditis sp. could potentially be an attractive option in the management of insect pests of cash crops.