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Maculinea arion

Hey, look at that!  It’s a delicate pale blue butterfly (Maculinea arion) from Europe and northern Asia. What could this ethereal creature have to do with the horror theme which this blog has been following as a lead-up to Halloween?  In fact, what does the butterfly have to do with any of Ferrebeekeeper’s regular themes?  Butterflies are lepidopterans rather than the hymenoptera we favor here.

As it turns out—the butterfly has a lot to do with hymenopterans.  Maculinea arion, or “the large blue butterfly ” to use its not-very-creative English name, may look innocent as a butterfly, but in its larval stage the creature is both appalling and remarkable.   Alcon caterpillars are myrmecophiles—which means the caterpillars live in association with ants.  Despite the Greek meaning of ”myrmecophile”  (to love ants) the relationship is anything but loving on the part of the Alcon caterpillar–unless love is meant in the same way as “to love ham”.

Maculinea arion (Large Blue) larva carried by ant (Drawing by Frohawk)

M. arion caterpillars are relentless predators of ant larvae.  The way they obtain this fragile foodstuff is remarkable for sophistication and ruthless guile.  When a caterpillar hatches, it lives for a few days on wild thyme or marjoram plants.  The caterpillar then secretes a sweet substance which attracts red ants which carry the larva back to their tunnels.

Inside the ant hive, the caterpillar produces pheromones and chemical scents which mimic those of the ant queen.  It also scrapes a small ridge on its first segment to produce the same noise as the ant queen. The ants are deceived by the caterpillar’s mimicry and they take it to the chamber where they rear their own larvae.  The ants wait on the caterpillar as though it were the hive monarch and they even feed it ant larvae—their own undeveloped siblings.  Once it pupates, the butterfly scrapes the inside of its chrysalis to continue the deception.  When the butterfly emerges from its cocoon the hapless ants carry it outside and guard it as its wings harden—whereupon the butterfly departs to mate and lay eggs on wild thyme or marjoram plants.

Phengaris alcon

The Maculinea Arion is not the only caterpillar to make use of this strategy.   The Phengaris alcon butterfly acts in almost exactly the same way.  Here is where the story becomes impressively crazy.   A parasitoid wasp, Ichneumon eumerus, feeds on the alcon caterpillar inside the ant hive.  The wasp infiltrates the hive by spraying a pheromone which causes the ants to attack each other.  While they are busy fighting, the wasp lays its eggs inside the caterpillar.  The wasp larvae hatch into the body of the caterpillar (which the ants think of as a queen) and they eat the caterpillar host safe in the cloak of this deception.

The parasitic wasp Ichneumon eumerus. (Image: J.Thomas/Natural Visions)

If an ant hive becomes too saturated with caterpillars it will die and all three species inside the hive will likewise perish).   The red ants in this scenario are constantly evolving new pheromone signals to outcompete the caterpillars and wasps—which in turn coevolve with the ants.  It’s strange to imagine the troubling world of deception, chemical warfare, and carnage just beneath the ground.

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