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Sith-Cada, Return of the Broodii

Just when you thought it was safe to start gardening again, Mother Nature has a surprise in store for us.  If the wild temperature swings we've seen this year wasn't enough, the ground is beginning to rumble to life.  The earthquake I'm talking about comes from a swarm of biblical proportions as Brood II makes it appearance from deep within our soil after its 17 year slumber.

Cicada's are nothing new to Virginians.  Every year annual cicadas appear, making themselves known as they sit in our trees producing a whirling call to attract a mate.  If surprised, the clumsy bugs take flight, buzzing loudly as they motor off to safety.  However, this 17 year Cicada, or technically called 'Magicicada' species is different because of the sheer amount that emerge from our ground in the next few weeks.  Some put the number around 30 billion, but a researcher at the Smithsonian Institute puts that number close to 1 trillion over its entire range.

Brood Emergence Timeline
When I first moved to Virginia, I got to experience Brood X (the biggest swarm) first hand.  Although many expected the damage to be immense, the trees still had leaves on branches and gardens remained the same as the brood retreated.  Of course, the sound of these horny critters searching for their soul mates drove you nuts, the next worst thing was smell of the deceased bugs as they littered the ground.  Birds had a good time snacking on these protein rich flying bug bars, after a while they even seemed to of had enough of a one sided diet.

So what can a gardener expect?  Fortunately, Cicada's have no functioning mouth parts capable of chewing a plant to pieces it does feed like an aphid on a plants sap. We don't need to think of them as a swarm of locust that will blot out the sun and lay crops to waste. These clumsy flying machines are only concerned with finding a mate, having sex and laying eggs. The last stage of laying eggs is where we can expect the most damage as the female splits the bark of small branches and lays anywhere from 600 to 800 eggs in the wound before she dies. Once the eggs mature, the nymphs hatch and fall back to the ground, disappearing for another 17 years. Although trees with significant damage from the egg laying process will invariably loose tips from branches, one shouldn't despair as trees quickly recover. It's nothing more than the Cicada's Barbers shop for trees, just taking a little off the back and sides.

So what benefit can come from all these Cicada's waking at the same time?  After all, events like this don't happen in nature without some kind of reason.  As it turns out, a researcher who studied the 2004 Brood X emergence found some positive repercussion following that outbreak.

It was discovered in the years following the 2004 outbreak, that there was an increase in plant growth stimulated from damage that had occurred by the Cicada's.  Also, as the larvae tunneled through the soil, it helped aerate the soil around the plants roots.  This tunneling reduced compaction of the soil and allowed moisture from rain or sprinklers to penetrated deeper into the soil.  Lastly,  the dying bodies of Cicada's actually became a great source of fertilizer.  As their bodies decay, it provided a valuable source of nitrogen and other nutrients that plants re-absorb.    

Scientist refer to this occurrence as a 'Resource Pulse'.  It is a term given to a large magnitude, but short interval and infrequent event where an resource availability was increased.  The study showed that plants given a diet of decaying Cicada's produced seed 9% larger than non-insect fed plants.  It's possible that a single acre of forest can yield up to 1 1/2 tons of nutrient rich dead bug carcass.  Those nutrients end up pouring back down the millions of finger sized holes in the ground from where they emerged.  In someways they return back to where they came from.

The whole ordeal is only expected to last 4 to 6 weeks before they all die after finding there one true love.  Its very Shakespearean to see a bunch of bugs sacrifice themselves so their species can keep on existing.  But one thing the press has failed to mention is when a species population explodes, so do the things that feed on them.  Ever heard of Cicada Killers?  Now there's a swarm of apocalyptic proportions!

Cicada Killer in action - Dendroica cerulea