The Elements of Evolution (48-8) Interspecies Interactions

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Interactions between species is a constant evolutionary driver. Sometimes a successful species falls prey to one that prefers the same dietary fare but lacks the skill to exploit it on its own. Such relationships can be complicated.

 Unhired Protection

The enemy of my enemy is my friend. ~ ancient Hindu proverb

With large colonies superbly organized, ants are a natural attraction to other species less endowed. Though relatively free of infectious diseases, thanks to their habitual cleanliness, ant societies are often invaded by social parasites.

Many ant pilferers escape punishment by passing themselves off as belonging to the colony, by having the proper scent to escape detection. Others are more brutish, in either forcing their way in or by brandishing chemical weapons. One particularly devious ant genus – Megalomyrmex – produces alkaloid venoms that repel and poison potential adversaries.

Some Megalomyrmex species get by on their own in small colonies. Others are raiders that loot the fungus gardens that attine ants cultivate.

Megalomyrmex agro-predators create havoc when they attack colonies. Fortunately for their victims, such raids are not very common. Only 1.5–14% of attine colonies are roiled by such parasitic raids.

Other Megalomyrmex settle in for the long haul. M. symmetochus has a cozy life as an unwelcome lodger in the nest of Sericomyrmex, an attine ant genus. Over 80% of Sericomyrmex colonies suffer the objectionable guest.

A newly mated Megalomyrmex symmetochus ant queen enters a host colony by stealth. She establishes herself in the fungus garden, where her growing band of parasites consume fungus and host brood for years.

The presence of M. symmetochus reduces the health of the host nest by slowing colony growth and reducing reproduction. The lodger clips the wings of host gynes (virgin queens), preventing mating flights. Clipped gynes become workers.

Like all lodger ants, M. symmetochus produces its own worker caste. In contrast, other social parasites exploit host workers without producing their own.

Once established, M. symmetochus never leave. The fate of their small colony is tied to that of their host.

Sericomyrmex is also subject to raider ants which can devastate a colony. When faced with such a threat, Megalomyrmex symmetochus earns its keep. The lodger attacks raiders with ferocity. Not only do they kill the invaders, they discombobulate them with their toxin. The raiding party may violently turn on itself, self-destructing because they no longer recognize their own kind.

M. symmetochus is so feared that its scent alone may dissuade raiders from even making an attempt on a nest.