Great Purple Hairstreak - Atlides halesus

Great Purple Hairstreak
Atlides halesus
Family: Lycaenidae

The complexities of ecology are so freaking mind-blowing!  This is a story of parasites on parasites, while also being a story of symbiosis, and a little commensalism.  Exactly!  Complexity!  Briefly, I will define some basic terms, in case your not familiar, that ecologists use to categorize relationships between different species.


Symbiosis - a relationship where both (all) species benefit from the interaction mutually.
Parasitism - one species benefits by doing harm to another species.
Commensalism - one species benefits from another species that neither wins or looses from the interaction.

An acorn germinates, sending a root underground.  Mostly unnoticed by us humans, the roots grow hair-like rootlets into the dimensions of the surrounding soil.  These roots and root hairs are then colonized by mycorrhizal fungus, that is, symbiotic fungus that greatly increase the surface area and, therefore, the uptake potential of the oak seedling's roots.  The Oak benefits by significant increases in both nutrient and water uptake - the fungus benefits by getting some of the Oak's carbon.

Thirty years later, the oak's branches offer an excellent perch for a foraging, fruit-eating bird, maybe a Scarlet Tanager, who has just nibbled on some mistletoe fruits on a neighboring oak tree.  Due to the rapid digestive systems of perching birds...SPLAT!  The mistletoe has a symbiotic relationship with fruit-eating birds.  The bird gets a snack, and the fruit gets dispersed, that is, moved to a new location.  Lots of fruit seeds get a "crappy" start.  The mistletoe seed germinates and grafts itself onto it's host oak branch, tapping, stealing, parasitizing the water resources of the oak.  This is where it gets really interesting for me.  The mistletoe is a parasite, but would lose out itself were it to kill it's host.  But, the oak has excessive mycorrhizal-fungus associations, symbionts, that greatly increase it's water uptake.  So now, the parasite, the mistletoe, is benefiting from, and perhaps dependent on, the symbiotic association of two other organisms, the oak and the mycorrhizal fungi.  By attaching to the oak, with it's increased water uptake, the mistletoe has chosen a good host that will be able to supply plenty of water without extensive damage that might kill the tree.  Sorry if this is sounding all over the place, but that's ecology, and it doesn't stop there.

Now, another parasite, flickering iridescent blue in it's wing beats, lands on the green, succulent leaves of the parasitic mistletoe.  The Great Purple Hairstreak, like almost all butterflies, has very specific parasitic relationships with very specific groups of plants, known by butterfly enthusiasts as host plants.  Let me explain something quickly.  Plants have evolved to deal with inevitable herbivory, the eating of plants, in many ways.  One of the plant kingdom's most potent strategies is chemistry.  Plants produce compounds that will poison any herbivore that eats too much of it's leaves.  Grasshoppers eat leaves constantly, but they are mobile, able to move between different species of plants, thereby avoiding an overdose on any specific plant compound.  Butterfly caterpillars, conversely, are not so mobile, they are stuck on the plant that their mother laid them as eggs.  Butterfly caterpillars eat incessantly.  As an analogy, they grow from the size of a human to the size of a whale in just around two weeks, at which point they begin their pupation period, and then become adult, flying butterflies.  Wow, that is a lot of eating!  In order to avoid being overdosed in their massive consumption, they have evolved a plethora of resistance strategies to deal with toxic biochemistry.  The Great Purple Hairstreak has evolved to deal with mistletoe biochemistry.

So there I was, on the phone with the volunteer coordinator at the Tennessee Aquarium, when she asked: "So, just to know if you will be a good fit for our program, what kind of stuff are you into?"  Right at that moment, Richard Candler, my ever-excited naturalist buddy, reached out to pass me a surprise insect he was holding in his closed hand.  In the passing, I could see a shimmering of blue on small, black wings, so I knew it was the elusive Great Purple Hairstreak.  With a grin, I answered to the TN Aquarium coordinator, "I'm into ecology!"