Myrmecophile dispersal via slave-making ants

In the new format “Natural History Notes”, Phil Hönle shares an interesting observation, including pictures, of two myrmecophiles that are transported (willingly or unwillingly?) from one nest to another when a nest is raided by slave-making ants.

A Note by Phil Hönle

Ants have a small armada of little arthropods that live within their nests. These so-called myrmecophiles (ant lovers) are often parasitic by making use of ants as a resource for food and shelter. Like all parasites, myrmecophiles face the problem of how to transmit to a new host, in this case, a new ant nest to live in. There are neat solutions to this problem. For instance, the small myrmecophile cockroach Attaphila climbs on virgin queens inside the nest, stays attached to them during the nuptial flight, and so accompanies the new queens during colony foundation. Here I report an odd myrmecophile transfer via a slave-making ant.

In Central Europe, one of the most spectacular ant species to observe is the slave-making ant Polyergus rufescens, also known as Amazon ant. Amazon ants make sophisticated raids on several Formica species, mainly from the Formica fusca group. They steal pupae and larvae during the raid and bring them to their own nest, where already present host-workers raise the raided brood to workers. These workers then behave quite normally as if they were still in their own nest. They even take care of the slave-making ants as if they were their sisters. Amazon ant raids can contain several hundreds of blood-red raiders, making for a quite spectacular show. I love to watch them, and they are common in some parts of Germany.

One day near Darmstadt, I noticed something strange: One of the larvae that were raided by the Polyergus workers had a small myrmecophile beetle attached to it, the clown beetle Hetaerius ferrugineus (thanks to the Kerbtier.de team for the ID; Figs. 1, 2). As it is common for these myrmecophiles, this fellow was most likely living inside the Formica colony, and when the raid happened it just clung onto the larva. Its new home will thus become the Polyergus nest. Of course, this is unlikely to be the usual way how Haeterius disperses, especially because these beetles are able to fly, given the fact that they can be also found outside of Polyergus territory. But nonetheless, I consider this an interesting observation.

I asked myself – was this a rare exceptional event or are there more myrmecophiles changing nests via the raids? The next few times that I stumbled upon a raid, I focused on spotting more such transfers – instead of taking more and more pictures ;). And indeed, I spotted an impressive mite that was feasting on one Formica pupa (Figs. 3, 4), now being similarly translocated to the Polyergus nest, where it will most likely snack on some further pupae. These observations make me wonder if Polyergus nests are subject to a comparatively high level of parasitism, since they frequently gather pupae from different host nests in the surroundings. Maybe Polyergus nests acquire relatively high parasite loads over time – thus functioning as a myrmecophile reservoir. Besides arthropod nest intruders, higher loads of pathogens such as viruses and fungi could similarly accumulate, which then need to be considered as a downside of living the raiders live. I could not find any mention of a myrmecophile transfer via slave-making ants in the literature, neither the mentioning of an exceptionally high myrmecophile load in Polyergus nests. Perhaps some of you can share interesting observations regarding this topic?

Fig. 1 Myrmecophile clown beetle Hetaerius ferrugineus, here inside a Formica fusca nest (© Phil Hönle).

Fig. 2 Myrmecophile clown beetle Hetaerius ferrugineus sitting on raided larva that is carried by a Polyergus rufescens worker (© Phil Hönle).

Fig. 3 Parasitic mite on a raided pupae that is being carried by a Polyergus rufescens worker (© Phil Hönle).

Fig. 4 Close-up of the same mite (© Phil Hönle).