A special symbiosis between butterflies and ants

As preannounced earlier in a recent post, today we talk about the relationship between some species of butterflies and ants. 

These ants are the same who live on the savannah acacias, like the whistling thorn acacia, which we talked about recently.

But let’s start from the beginning. 

About 75% of the Lycenids, the second-largest family of butterflies behind Nymphalidae, show a close relationship with ants.
For about a third of them, this relationship is so essential that these butterflies would not be able to survive without the ants.

18

SEPTEMBER 2020

Butterflies
Ants
Symbiosis

Instead, for half of them this relationship is less crucial to their survival and requires the production of honeydew for the ants who will protect the butterflies in return.
This relationship is called myrmecophily.

To understand this topic very well, it is better to review butterfly life cycle:
butterflies lay eggs on a plant and the eggs hatch into caterpillars. Caterpillars finally pupate and emerge as an adult, after 5 stages (instars).
Lycaenid caterpillars feed on the plant they hatched on.
Deudorix dinochares
Some of them use chemical agents and some use specific sounds to attract the ants who are convinced, in this way, to look after and protect the caterpillars. These latter feed the ants with honeydew produced by a gland on their back. Some of them also possess tentacle organs flanking the dorsal nectary organ, and they use them to push the ants to shelter them more and more by everting these structures.

But there are some species of Lycenids that don’t attract the ants in their first larval stages but fall off the plant. They wait on the ground paciently, until an ant finds them and begins to feed on the honeydew produced by their dorsal nectary organ.

 

This is when the caterpillar begins to behave like an ant larvae and instinctively the ant takes it to its ant nest. Unfortuntately for the ants, the caterpillar becomes a predator, feeding on ant eggs and larvae.

The caterpillar also is able to produce some chemicals that make the ants think it is just a big ant larvae, so they won’t attack it. When ready, it will pupate, still protected by the ants, and emerge as an adult.

       Source: piercelab.oeb.harvard.edu

Vachellia drepanolobium and ants

One African species of Lycenid, Anthene usamba, is closely related to one of the most aggressive whistling thorn ants (we talked about these ants and their relationship with acacias just in a recent post). The female butterfly in fact looks for whistling thorn acacias, Acacia drepanolobium, with the specific host ant Crematogaster mimosae, and avoid neighbouring trees with other ant species . Once found it, the eggs are laid on the foliage and young branches of the plant.

When the eggs finally hatch, the caterpillars are protected by the ants and brought inside the domatia, the swollen thorns which are used by the ants as nest sites, and here they live in close association with the acacia ants, and each larva occupies a domatium singly. Here the caterpillars are also fed mouth to mouth by adult workers via trophallaxis (regurgitation). If necessary, the caterpillars may also eat on ant larvae. Pupation occurs inside the domatia and the adult butterfly emerges, departing through the hole chewed by it. The adult females remain closely associated with their natal patch of trees, while the males disperse more widely across the acacia savannah.

Close up of a whistiling thorn acacia domatia

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