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
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PHOTOS:
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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| #1 |
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| #2 |
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| #3 |
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| #4 |
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| #5a |
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| #5b |
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| #6 |
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| #7 |
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| #8 |
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| #9 |
Last week's sudden "cold snap" must have really gotten the attention of
doves living to the north of Iowa. By Thursday afternoon [Aug 16] dove
numbers appeared to be showing a noticeable increase across North Central Iowa.
