This study is the first exploration of ecological relationships between ants, aphids, and black-eyed pea (Vigna unguiculata).  Black-eyed pea produces nectar in extrafloral nectaries (EFNs), on stems and leaves. EFNs attract ants that consume EFN nectar and protect plants from herbivores. This ant-plant facultative mutualism can be disrupted when aphids are present. Aphids are phloem-sucking herbivores that provide sugar to ants by excreting “honeydew”. Aphids can parasitize the ant-plant mutualism by stealing the plant’s sugar and stealing protection from the ant “bodyguards”. Aphids colonized plants during the preparation of the field plot, but initial population size was low. After ants (Camponotus spp.) established themselves on plants in the field plot, aphid numbers increased very rapidly, and we observed aphid-tending behavior by ants. In addition to herbivores, the abundant aphid population attracted a variety of predatory insects. Presence of ants had a negative effect on shoot and fruit weight; means for ant exclusion treatments were higher than the ant inclusion treatments. Adverse outcomes for plants with ants likely relate to high costs of ant-tended aphids removing sugar from the plants. The lowest plant growth and reproduction was seen in plants with ants and sealed EFNs. Aggressive aphid tending behavior is likely on these plants since ants received no EFN-nectar. Interaction between ants and nectar effects on shoot and fruit weight showed a trend for less severe negative effects of ants when nectar was available. More research is needed to understand how interactions shift as ecological communities change because ants can be allies or enemies to EFN-bearing plants. Vigna unguiculata is a critical source of global food security in the face of climate change threats.  This study may provide ecological insights for ways to employ agroecological approaches to increase yields of black-eyed pea in the future.