We deal in this paper with light trapping results of the Heart and Dart (Agrotis exclamationis Linnaeus, 1758 Lepidoptera: Noctuidae), depending on the horizontal component of the geomagnetic field (H-index). We calculated relative catch vales from the hourly collecting individuals of examined species by generation. These hourly relative catch values were classified to the hourly values of H-index. These hourly catch results were correlated to the hourly values of H-index. We calculated correlations to demonstrate the supposed relationship between the two data. Our results suggest that more effective light trap catch belongs to higher H-index values.