While their function is not always clear, and may be related to regulation of sugars, in most cases they appear to facilitate plant insect relationships. In contrast to floral nectaries, nectar produced outside the flower generally have a defensive function. The nectar attracts predatory insects which will eat both the nectar and any plant-eating insects around, thus functioning as 'bodyguards'. Foraging predatory insects show a preference for plants with extrafloral nectaries, particularly some species of ants and wasps, which have been observed to defend the plants bearing them. "Acacia" is one example of a plant whose nectaries attract ants, which protect the plant from other insect herbivores. Among passion flowers, for example, extrafloral nectaries prevent herbivores by attracting ants and deterring two species of butterflies from laying eggs. In many carnivorous plants, extrafloral nectaries are also used to attract insect prey.