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Karma is very quick sometimes. Jet ants make their nests inside those of other ants, ultimately taking them over. But they are also victimised by pests of their own.
Jet ants (Lasius fuliginosus), alternatively known as shining black ants, live in Europe and Asia. When the workers of this species go foraging, they mark their trails with secretions that contain a special blend of pheromones. Many foraging ants commute on these trails, transporting honeydew collected from aphids and other insects in special stomachs called “crops” that they use for storing food.
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However, sap beetles (Amphotis marginata) spend their lives on these foraging paths and dupe food-laden ants into regurgitating meals for them. This is known as kleptoparasitism, in which one animal steals food gathered by another.
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Now, Bert Hölldobler and Christina Kwapich at Arizona State University in Tempe have found that the beetles get most of their food this way.
Take my lunch!
The pair observed A. marginata beetles living near ant colonies in the wild and collected both species for experiments in the lab.
“Ants feed each other honeydew collected in their crops by essentially vomiting into each other’s mouths,” says Kwapich. “The beetles have capitalised on this behaviour. We call them ‘highwaymen’ because they rob the traffic on the ants’ foraging trails.”
To do this, a beetle approaches an ant and taps on it with its front legs and antennae, after which the ant briefly licks the beetle’s head. Then the beetle presses its own mouthparts on those of the ant, encouraging it to regurgitate a big drop of food.
“It’s sort of like a secret handshake, followed by the beetle sticking its finger down the ant’s throat,” says Kwapich.
Sneaky beetles
Hölldobler and Kwapich tracked the spread of food between the creatures by feeding ants radioactive honey water. They found that beetles placed among fed ants obtained 1.8 times as much food as other ants did from their own kind. Beetles never transferred food to unfed ants or to other beetles, so the relationship is strictly one-way.
They also found that A. marginata have glands on top of their heads that secrete liquid. Kwapich says these secretions might be attractive to an ant, and when it gets in close to investigate, the beetle can touch its mouthparts to those of the ant and induce regurgitation.
Occasionally, an ant realises the beetle is an intruder and attacks it. But the beetle has a trick: it retracts its appendages under its protective wing covers and flattens itself on the ground like a little suction cup. The ants cannot flip the beetles when they do this.
“A huge diversity of arthropods specialises on ant colonies, and many of them are kleptoparasites,” says Joseph Parker at Columbia University in New York. But he says species such as A. marginata, which are fed mouth-to-mouth by ants, are less common.
“This requires breaking the ant’s behavioural system of food solicitation, and so it is harder to achieve evolutionarily.”
Journal reference: PLoS ONE, DOI: 10.1371/journal.pone.0180847
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