Ants, Butterflies, and Wasps: A Tale of Mutual Dependence

The Life Cycle of Phengaris rebeli (image via http://sciencythoughts.blogspot.com)

It’s October—the month of costumes, masks…and monsters.  To start out this year’s Halloween season on an appropriately ghastly note, today’s post deals with a horrifying creature which relies upon disguise to feed itself: namely, the Mountain Alcon Blue butterfly (Phengaris rebeli).

Native to temperate grasslands of Central Europe, the Mountain Alcon Blue has silvery blue which are stippled in little black spots with delicate white edges. The butterfly flits harmlessly about in gentle meadows, finds a mate, and then the female lays her eggs on a pretty gentian flower.

Aww, it’s on a pretty flower (Photo by Tristan Lafranchis)

So why is this delicate alpine beauty a creature of nightmares? When the Mountain Alcon blue larva hatches, it eats the gentian until it reaches a certain size whereupon it falls to the ground and releases an allomone—a deceptive chemical which makes it seem identical to an ant larva. Foraging ants discover the caterpillar and tenderly carry it deep within the protection of the ant hive to the nursery room where the ant larvae are fed and cared for.  Then the caterpillar reveals another dark talent: it produces a sound which perfectly mimics the ant queen.  Subject to this all-powerful voice of authority, the ants care for the caterpillar as though it were the queen–even going so far as to attack the actual queen.  Obeying the dictates of the awful song, the ants feed the still living ant larvae to the caterpillar which devours the helpless young ants like so many little wiggling burritos (well, if juvenile butterflies ate burritos).

Caterpillar with slave ant (photo by Darlyne A. Murawski)

When the butterfly pupates into an adult, it loses its ability to mimic ant chemicals or produce the queen’s voice.  The ants recognize it as an invader and attack, but the butterfly’s scales are designed to resist their mandibles.  It flees the crippled and abused ant colony and begins the cycle over again.

Isn’t nature beautiful? (photo by Guy Padfield)

Yet monsters still must fear other monsters and there is an even more invidious predator which seeks out the Alcon larvae deep within ant hives. This is the parasitic wasp, Ichneumon eumerus, which infiltrates ant colonies which are being preyed on by Phengaris rebeli larvae.  The wasp locates the caterpillar and then releases an allomone which causes the ants to go insane and attack one another.  Then in the chaos that follows, the wasp injects its eggs into the living caterpillar.  When the eggs hatch they eat the interloper from inside and then burst out of its carcass.

The parasitic wasp Ichneumon eumerus preying on Phengaris caterpillar while an ant stands by waiting for doom. (Image: J.Thomas/Natural Visions)

Advertisement