A Greek Tragedy Inside an Ant Colony
In 2021, Japanese ant enthusiast Taku Shimada collected a newly mated *Lasius orientalis* queen and placed her into a *L. flavus* colony to observe how a socially parasitic queen stages a takeover. He witnessed something extraordinary: the host workers began attacking their own mother, biting her, tearing off her antennae, and dragging her out of the nest chambers while the intruder queen stood nearby. Three days later the host queen was dead; a day after that her body was dismembered and discarded. The workers then gathered around the parasitic queen, groomed her, fed her, and began tending her eggs.
Shimada posted the footage to his blog AntRoom. Three years later, Kyushu University researcher Keizo Takasuka found the video and later said he was left speechless. On November 17, 2025, the work was published in *Current Biology* under the title "Socially parasitic ant queens chemically induce queen-matricide in host workers."
Why Matricide Is Almost Unheard Of
In eusocial insects, workers carry the queen's genes and depend on her continuous egg-laying for their genetic future. Killing a healthy, laying queen is essentially destroying one's own lineage. The few previously documented cases of matricide, including matriphagy in earwigs, pseudoscorpions, and spiders, or workers eliminating a failing queen, all benefit the killers. The Takasuka study is the first known example of matricide that benefits only an unrelated outsider.
The Four-Step Chemical Coup
Step 1: Chemical disguise. The parasitic queen spends a night in contact with host workers and brood cocoons, absorbing the colony's cuticular hydrocarbon signature. This lets her pass the guards at the nest entrance.
Step 2: Infiltration and location. Once inside, she navigates the maze of chambers and locates the host queen, likely by following queen-specific chemical cues.
Step 3: Chemical attack. The parasitic queen sprays formic acid from her acidopore directly onto the host queen. *L. orientalis* queens sprayed roughly 15 times over 20 hours; *L. umbratus* queens achieved the same effect with just 2 precise sprays. Formic acid is the universal alarm and defense substance of the subfamily Formicinae, and a large pulse of it signals an intruder attack.
Step 4: Workers kill their own mother. Coated in formic acid, the host queen no longer smells like kin. Workers read her as an enemy and begin sustained attacks. *L. flavus* workers took about 4 days to finish the job; *L. japonicus* workers dismembered the queen shortly after the second spray. The parasitic queen never touches the host queen herself; she simply waits.
Step 5: Usurpation. Once the host queen is gone, workers accept the parasite, feed her, and rear her brood. As the original workers age and die, the colony is entirely replaced by the parasite's offspring.
Manipulating Cognition, Not Just Behavior
Takasuka previously studied the ichneumonid spider ectoparasitoid *Reclinervellus nielseni*, which hijacks the orb-weaving spider *Cyclosa argenteoalba* and forces it to weave a reinforced "cocoon web" before being consumed. That case is behavioral hijacking: the spider is still executing a web-building program, but with altered output.
The parasitic ant case goes deeper. The workers are not forced to attack; they genuinely re-identify the host queen as a threat. The parasitic queen has rewritten the workers' identity-verification system rather than merely commandeering their limbs. The distinction is the difference between forcing someone's hand and rewriting their beliefs about who the enemy is.
A Spectrum of Host Manipulation
- Motor control: *Ophiocordyceps* fungi drive infected ants to bite onto leaves in optimal positions for sporulation.
- Appearance: *Leucochloridium paradoxum* flukes turn snail tentacles into pulsating, colorful bait that attracts birds.
- Behavior: *Reclinervellus nielseni* reprograms spiders to build cocoon webs.
- Cognition: *Lasius orientalis* and *L. umbratus* rewrite worker kin-recognition so the mother is read as an intruder.
- Shimada, T., Tanaka, Y., & Takasuka, K. (2025). Socially parasitic ant queens chemically induce queen-matricide in host workers. *Current Biology*, 35(22), R1079-R1080. https://doi.org/10.1016/j.cub.2025.09.037
- Takasuka, K., et al. (2015). Host manipulation by an ichneumonid spider ectoparasitoid. *Journal of Experimental Biology*, 218(16), 2321-2328.
- Mongabay. 5 unexpected animal behaviors we learned about in 2025.
The progression moves from legs to body to behavior to identity recognition, each step deeper into the host's "self."
Why Formic Acid Works
Formic acid is a shared alarm signal across Formicinae. Workers are hard-wired to interpret heavy formic acid in the nest as an intruder. The parasitic queens exploit this universal language by transferring the signal onto the host queen herself. The defensive system remains fully functional; it is simply aimed at the wrong target.
Two Species, One Strategy
*L. umbratus* parasitizing *L. japonicus* uses the same acid-spray-and-matricide playbook despite being distantly related to *L. orientalis*. The convergence suggests this is an optimal solution: any parasite that can rewrite identity recognition in a Formicinae colony can take it over without direct combat.
Implications
The authors frame the phenomenon as a biological analogue to prompt injection in AI security and to trust hijacking in cybersecurity. A trusted identity-recognition system continues to run perfectly, but on falsified input, and therefore produces destructive but internally consistent outputs. The workers did not malfunction. They executed their program faithfully on bad data.