The myrmecophile community within red wood ants was my initial study system, and the majority of my current projects still focuses on this specific system.
The vast nest mounds constructed by red wood ants are remarkable stuctures across Eurasia's temperate and boreal forests and heathlands. Appreciated for their pivotal roles, red wood ants act as top predators capable of managing pest insect outbreaks. They also foster nutrient diversity in forests by concentrating food and organic matter within their mounds while shaping both living and non-living components of forests beyond their nests.
Moreover, the presence of these ants is crucial for numerous associated species residing within or near their mounds. In temperate ecosystems, red wood ants support most species of myrmecophiles. We find mainly mites and rove beetles, but also isopods, springtails and spiders are abundant. About 125 species of obligate myrmecophiles live in association with red wood ants together with a large group of arthropods (e.g. common rough isopod) facultatively residing in their nests (PDF).
The remarkable diversity among RWA myrmecophiles primarily stems from the structure of RWA nests. Their large mounds offer stable habitats with regulated temperature and moisture levels. These mounds exhibit heterogeneity in temperature, moisture, and materials (organic thatch, inorganic soil, and a central stem) generating a variety of microenvironments. Additionally, a constant supply of food and organic material sustains various trophic groups, including parasites, predators, scavengers, detritivores, and fungivores. Some myrmecophiles are attracted to aphid colonies tended by the ants and found near the mounds.
We found that many of these myrmecophiles have a detrimental impact on their host ant, as they either consume the brood or pilfer the collected prey. However, some of these myrmecophiles also feed on organic nest material or prey on other myrmecophiles. As a result, each nest mound supports a local food web involving detritivores, scavengers and predators (PDF). The community of myrmecophiles in mound building Formica ants come close to an ideal model microcosm. They form multilevel food webs in spatially delineated habitat islands. These habitat islands are long living, easy to track and have a distinct distribution. Therefore, they are ideals systems for studying large-scale spatial and temporal community processes. Red wood ants are also heavily dependent on mutualistic aphids that live in the trees and on plants near the nest.They secrete sugary honeydew which may constitute no less than 90% of the colony dietary needs. In return for a constant flux of honeydew, red wood ants heavily protect the obligatorily associated aphids. As such, the red wood ant microcosm not only encompasses different functional trophic groups of arthropods, but also stretches across the complete gradient of symbiosis from parasitism to mutualism.
some key insights of my research on red wood ant myrmecophiles:
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Connectivity of nests and nest age positively affect myrmecophile abundance and diversity (PDF).
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Myrmecophile species have different location preferences in the heterogenous red wood ant nest habitat (PDF).
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Abiotic (PDF) and biotic (PDF) indirect effects affect the species interactions in the microcosm .
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Imitating the chemical signals (cuticular hydrocarbons) used by the host for recognition is mostly absent in red wood ant myrmecophiles (PDF). Instead they resort to behavioral strategies such as prudent behaviour, hiding and emitting repellent substances (PDF).
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Moving outside the nest is rarely observed, but using pitfalls around the nests, we could demonstrate that they are very mobile and can move up till 25 m from the nest. They do not move in a random way, but closely follow the ant foraging trails to move. Some myrmecophiles also track the red wood ant host when it relocates to another nest (PDF).
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Food chain length and the trophic positions the myrmecophile community was strongly affected by the host's foraging decisions. When the host diet shifted from predominantly herbivorous to more predacious, the trophic position of the symbionts and food chain length strongly increased (PDF).
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The myrmecophile community undergoes a successional shift when the host nest ages. Young nests are dominated by facultative groups, but in old nests obligate group become more important. This shift is translated in a higher stability of the community.
Myrmecophiles in red wood ant nests can reach high densities. This figure gives the beetles (1935 individuals, 11 species, every dot is a beetle) found in a hibernating nest fragment of Formica rufa (PDF)
Nests of red wood ants as microcosms supporting myrmecophile food webs with predators, intermediate predators, scavengers, detritivores and fungivores. Ants bring organic material, honeydew and prey into the nest environment
Typical myrmecophiles associated with red wood ants
Clytra quadripunctata
The biology of Clytra quadripunctata is rather peculiar. The adults are adorable beetles that feed on plants near the nest. After mating, the female drops her eggs. The larvae enter the nest and remain there probably for 2 years. Lab tests demonstrated that the larvae are brood predators and scavengers (PDF). They preferentially reside in the heated brood chambers in the centre of the nest (PDF). The larvae of this beetle are protected by a pear-shaped case in which they can retract. After pupation, the adults sneak out of the ant nest.
Some years ago, I observed that a red wood ant colony was moving to a new nest site a couple of metres away. As I have been curious for a long time how myrmecophiles would respond to the desertion of their home, I carefully inspected the horde of moving workers. To my surprise, I saw that a group of larvae of the beetle Clytra quadripunctata were crawling among the moving colony towards the new nest site. A bit later, some larvae were also dragged by the workers to the new nest (PDF).
Coccinella magnifica
Coccinella magnifica is a myrmecophile that does not live inside the host nest. The ladybird (and its larvae!) lives near the aphid herds tended by red wood ants around their nests. It verociously feeds on these aphids and shows some behavioral adaptations compared to its sister species C. septempunctata to avoid ant aggression.
Coccinella magnifica with Formica pratensis
Thyreosthenius biovatus
This small linyphiid spider is very common. Before I started my PhD, there was only 1 record of this spider in Belgium. Since then, I find them in almost all sampled red wood ant mounds. This spider is one of the top predators in the myrmecophile food web. It feeds on different other myrmecophiles, including springtails, mites and beetle larvae. In lab trials it also feeds on red wood ant eggs, but probably this is not its main food source (PDF). The spider is mostly ignored and hardly provokes aggression (PDF).
Mastigusa arietina
This spider has a broad host range. I found them with red wood ants, Lasius fuliginosus and Formica fusca (PDF) It provokes much more aggression than T. biovatus and is killed when no shelter is available (PDF). It is a predator that feeds on other myrmecophiles such as the springtail Cyphoderus albinus (see photo). The white egg sacs are attached to wood pieces in the nest.
This white and blind springtail is omnipresent in red wood ant mounds. It is a myrmecophile with a broad host range and also easily be found in nests of other ant species (PDF). It is a typical detritivore but can also feed on prey collected by the host. It is an important food source for different predatory myrmecophiles
Cyphoderus albinus
Rove beetles
Rove beetles are the most diverse group in the red wood ant myrmecophile community. Most of them are typical scavengers, that also feed on ant brood (PDF). The beetle Stenus aterrimus is atypical as it actively hunts for prey. Dinarda maerkelii is the only beetle that is able to steal food droplets from its host. These beetles do not resort to chemical imitation of the host's recognition cues, but use avoidance behavior and emitting repellent secretions (PDF).
A. Dinarda maerkelii, B. Stenus aterrimus, C. Thiasophila angulata, D. Lyprocorrhe anceps, E. Amidobia talpa F. Thiasophila angulata G. Notothecta flavipes
Hypoaspis oophila
This peculiar mite typically lives on the eggs of Formica ants. It seems not to damage or puncture the eggs, but rather licks the secretions on the eggs.