For many predators, both vertebrate and invertebrate, caterpillars are tasty bundles of nutrition and are eagerly hunted. To avoid getting eaten, caterpillars have evolved various strategies, including camouflage, having irritating hairs on the body, and even incorporating toxins into their own tissues.
One unusual method is seen in caterpillars of the butterfly family Lycaenidae. This family includes the blues, coppers, and hairstreaks, such as this Eastern pine elfin (Callophrys niphon) and banded hairstreak (Satyrium calanus). Lycaenid caterpillars enlist the help of ants for protection by secreting a nectar-like fluid from glands on their body. The ants feed on this, and in turn protect the caterpillar from predators.
Many ant species in the genus Camponotus are part of these mutualistic relationships, such as this young queen Eastern black carpenter ant (Camponotus pennsylvanicus).
This type of relationship with ants has evolved many times, with other types of insects, or even some plants, being the ants' partners. Have you ever thought about the ants that seem to always be on the flower buds of peonies? Peonies have nectaries that are outside of the flower, attracting ants to feed on the unopened buds, and help keep away herbivorous insects such as thrips and other pests. At Thuya, we often see Formica podzolica ants on our peonies.
Every story needs a villain, and in this case, we have a good one - the introduced European fire ant (Myrmica rubra). As if their painful sting wasn't enough reason to dislike them, they also drive away native ants and lead to a decline in ant diversity. Native ants play several important roles in the ecosystem, and all these are compromised when they are driven out of an area. For the lycaenid butterflies, the presence of fire ants can lead to a loss of protection from predators.
Of course, villainy can be matter of context. In their native Europe, fire ants have a completely different relationship with lycaenid butterflies. At least two species of butterflies there also secrete from glands, but instead of a nectar-like substance, it is a pheromone mimic that tricks the fire ants into bringing the caterpillars to the ant nest and feeding them like their own young. In this case, the fire ants are victims of nest parasitism. Who knew fire ants could be tricked so easily?