I have been monitoring and studying a small Pheidole megacephala cluster the last month, and during that time was present during three instances of direct aggression between it and another species. I will add here a few notes on what I have observed during those three instances.
(1) The main tactic of PM is one that is employed by other ant species. That is, minor workers engage with the intruder and try to pin it down. They usually grip moving appendages, such as legs and antennae, but they will also grip the stinger of the intruder if that is present. Normally, the stinger area is gripped last due to its smaller nature.
(2) Roving major workers will encounter these pinned intruders and start to cut off appendages, such as the legs. They can also work on the connection between the head and the thorax, as well as the petiole and postpetiole. I have seen several instances of beheaded intruders as well as those whose gasters have been snipped off. The abdomen of the intruder might also be crushed, and I have seen one instance of this. I may also have observed instances where the major workers tries to crush or break off the mandibles of the intruder.
(3) If a major worker encounters an intruder first and it is large, it will try to pull the intruder back towards the mass of PM, where minors and other majors can assist.
(4) Killed intruders are taken to the nest, and are likely treated as prey.
(5) Major workers (and perhaps minor workers) might be using chemical repellants or chemical alarms that are repugnant to other ants. I have seen one instance of a major worker standing still with gaster raised and perhaps vibrating. The surrounding enemy ants stayed clear for awhile. I have also seen intruders seemingly repelled from 10 cm away from massed congregations of PM around baits (although the possibility exists they are repelled by alarms from nestmates who have been immobilized and are being killed by the PM nearer the baits.
(6) In defending baits, both majors and minors may loop farther away from a bait and create a buffer between the bait and any foragers. This looping tactic might be initiated when a worker encounters an intruder away from the bait.
(7) Majors in combat hold their antennae in a fixed and stereotypical position (see image below), with the antennae held firmly flat against the head and angled back.
(7) When masses of intruders (in this case fire ants Solenopsis invicta) aggressively harass exposed foraging lines, they may withdraw and engage the intruders within enclosed foraging areas.
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