Monday, July 30, 2012

Creation Corner with Lowell Washburn

             Summer Dog Days Provide Sultry Backdrop for Predator & Prey
                              By Lowell Washburn

The Dog Days of summer are upon us.  August is just around the corner and, right on schedule, this year’s crop of annual cicadas are making their above ground debut.  Within hours of their appearance, the distinctive chorus of hopeful males began to fill the humid afternoon air.  The “scissor grinder’s” trilling is impossible to miss.  Surpassing 100 decibels; the sound is the insect equivalent of a power saw and can easily be heard above your neighbor’s roaring lawn mower.

For many folks, the cicada’s song provides an audible reminder that summer heat is on borrowed time.  For others, the harsh buzzing is regarded as just one more item on the growing list of hot weather annoyances.  But for the giant cicada killer wasp, the outlook is much different.  As far as this formidable amber-winged predator is concerned, the cicada’s noisy rattling is simply the sweetest music ever heard.  For currently emerging cicadas, the huge wasps represent the very worst nightmare the world has to offer.

For anyone who has had an opportunity to admire a specimen at close range, it will come as no surprise that the giant cicada killer is Iowa’s largest species of wasp.  For weeks now, these solitary hunters have been busily preparing for the annual emergence of adult cicadas.  After selecting a well drained, usually sandy location, female wasps begin digging elaborate tunnels containing several side chambers --- kind of like the hallway of a subterranean hotel.  Although cicada killer wasps are solitary [meaning they don’t live in large, highly organized colonies] multiple females may share a single tunnel.  Although most excavations are smaller, tunnels can go as deep as two feet and extend for five or six feet.  

Once a side chamber is completed, the female who dug it immediately goes on the hunt for cicadas.  Searching the upper canopy of deciduous forests and urban shade trees, the predacious wasps appear to relentlessly scour each and every leaf in search of game.  I’ve read that cicada killers readily home in on the sound of singing [male] cicadas.  Sounds reasonable, except that the wasps I’ve spent time observing bring in at least as many female cicadas as they do males.  Even if cicada killers do use sound to locate prey, it seems to me that visual cues must be equally important.  Here in north central Iowa, the past week was easily the best for wasp watching so far this summer, with individual hunt times running as low as 12 to 15 minutes.  Cicadas being brought to the lek I have been observing ran about 2 females for each male, with peak hunting activity occurring at a time when the buzz of male cicadas provided a constant audio backdrop.   

Regardless of what hunt strategy is actually employed, there are some constants.  As soon as an adult cicada is located, the wasp delivers a powerful sting; injecting a potent shot of venom that immediately overpowers and totally immobilizes its victim.  The powerful wasp then airlifts its heavy cargo back to the tunnel.  The higher the cicada is located in a tree, the easier the flight back home.  In spite of the cicada’s weight and bulk, the incoming wasp usually dead centers the tunnel’s entrance so precisely that you barely have time to catch even a fleeting glimpse before the cicada and its captor disappear into the hole.  On windy or extremely humid days, incoming wasps seem more likely to miss the mark and may end up having to drag their cargo the last few inches to the tunnel.

Once an immobilized cicada is spirited below ground, the scenario’s creep factor escalates dramatically.  What began for the cicada as a sunny afternoon of singing in the treetops has suddenly become a living nightmare of Stephen King proportions.  But the worst is yet to come, and what lies ahead for the comatose insect isn’t likely to make the Mother Goose list of suggested bedtime readings for toddlers any time soon.  In the true life world of the outdoors, Walt Disney story lines are few and far between; and fact is often scarier than science fiction.  Let’s continue.

Upon finally reaching the inky blackness of its preprepared underground chamber, the female cicada killer drops her prey onto the floor the cramped room.  She then lays a single egg on her victim.  Mission accomplished, the wasp seals the chamber’s entrance with a sodden door and leaves.  Like a fresh side of beef hanging in the local locker, the cicada lies on its back and waits.  In two or three days the attached egg hatches, and the wasp larvae immediately begins to devour its helpless, protein packed host.  Meanwhile, the female is busy constructing new ‘guest chambers’ and continues filling the nursery -- one stunned cicada at a time.  Although their time is short -- all adult wasps will die before winter -- the predators make the most of what days they have.  During the four weeks or so that it will spend on the hunt, a female may capture 100 or more cicadas.

With its amped up demeanor, pulsing abdomen, bright colors, loud wings and huge size; Iowa’s giant cicada killer wasp projects an ominous air.  But in reality, humans have little to fear.  For the most part, cicada killers are all about the hunt.  Unlike colony nesting wasps and hornets whose lives are directed toward protecting a communal hive, cicada killers are extremely tolerant of human intrusion --- at least under most circumstances.  Even though I’ve given tunnel digging and cicada toting females plenty of just provocation to sting, the harshest rebuke I’ve received so far was a stern warning rattle of the wings -- at which point I immediately backed off and let the creatures go.  I think the females are simply conserving their venom for future cicadas, or maybe they just think I’m too big to drag down the tunnel.
Final Thought:  The wonders and complexities of creation are never fully explored, nor are they ever completely understood.  Things that appear simple at a glance, rarely are.  The inseparably intertwined lives of the annual cicada and the cicada killer wasp present a portrait of two seemingly disconnected and unrelated species each living out the adolescent stages of their lives in complete ignorance of the other, yet both headed on a direct and completely predictable collision course to an unavoidable convergence that will occur, right on schedule, late each summer.

Cicadas that survive predators will deposit their eggs in slits they slice into the bark of tender tree branches.  Cicada eggs hatch, nymphs drop and borough into the ground where they will spend the next three to five years using spear-like siphons to tap tree roots for sap.  When the timing is perfect, maturing nymphs suddenly tunnel to the surface.  Climbing a nearby tree trunk, the nymph splits its plastic-like skin down the back and the anvil headed, clear winged adult we all recognize emerges.  Within hours, the sound of singing cicadas fills the sultry summer air.  Although the adults are actually at least three or more years old, they are called annual cicadas because “a hatch” emerges above ground each summer.

Right now, the first cicada killer eggs have already hatched and larvae are voraciously consuming their paralyzed hosts -- one stunned cicada for baby males, but two or three for growing females [The mother knows in advance which gender an egg will become].  Once the meal is complete, larvae will spin a cocoon of sorts and then go dormant for the remainder of the summer, fall, and winter in the underground room its now deceased mother constructed.  The wasp larvae will pupate late next spring, and the annual crop of giant cicada killers will appear, right on schedule, in late July of 2013 --- just in time to make hurried preparations for the impending emergence of the annual cicada when, with all the precision of a finely crafted Swiss watch, the lives of two seemingly unrelated species will converge in perfect synchrony.      
To every thing there is a season, and a time to every purpose under heaven.
                                                      Ecclesiastes 3:1                                                                                               

 1 -- A female cicada begins digging its tunnel
 2 -- With side chamber completed, the wasp begins the hunt
 3 -- A newly emerged annual cicada
 4 -- Incoming - An adult female brings home the bacon
 5 -- A female cicada killer [Tunnel #9] and its prey
 6 -- A female cicada killer [Tunnel #6] and its prey
 7 -- A female cicada killer drags its heavy cargo into Tunnel 6
 8 -- Another female leaves the lek to search for cicadas
 9 – Adult female









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