If one pays close attention, the changing seasons are often well-advertised. These happenings, which mark the progression of nature’s calendar, offer an everchanging series of fascinating and entertaining events. Obvious examples might be the fall changes in leaf color here in our deciduous forests. In spring, the plaintive croaks of the diminutive chorus frogs announce that winter is over, or nearly so. The arrival of northern harriers and short-eared owls from their northern haunts is a good indication that winter is upon us.
But sometimes, the seasonal events are not so lavishly noticeable. I was recently reminded that, even in the heat of summer, I should keep my eyes open. If not, I might miss the chance to see one of nature’s seasonal dramas taking place right at my feet.
Strolling along recently, I happened to glance down at a sandy embankment that gently sloped away from my path. A blast of sand resembling a tiny river’s alluvial fan flew outward from a small hole in the ground. As I stopped to watch, the architect of this little project came backing out of the burrow. It was a wasp species known as a cicada killer, one I was familiar with and enjoy seeing because of its size and fascinating behavior.
And yes, they are frighteningly large. At nearly two inches in length, their robust body size makes them appear quite intimidating. Fortunately, cicada killers are not aggressive. The males are stingless, but the females can pack a wallop, especially if you happen to be a cicada. I have never been stung by one and, in fact, can’t recall knowing anyone who has. They don’t have the aggressive territoriality of wasps like the bald-faced hornet or yellow jacket. My experience has been that one can walk quite near cicada killers without any reaction on their part.
August seems to be the peak season for the burrowing activity of the cicada killer. But just why are they burrowing? Herein rests the reason I find them so morbidly fascinating. First, as their name suggests, they do hunt cicadas (around here people tend to call cicadas locusts, but that’s a different story). Normally these are the annual cicadas we can encounter every year, as opposed to the species which erupt periodically.
The wasp’s prey is killed, but not by the sting of the female. The plot thickens! The female will construct a burrow in dry, sandy, or loose soil that may be a foot or slightly more in depth. The burrow may be a couple of feet long or may extend several feet. Typically, there are side chambers too, often over a dozen.
The female cicada killer will then go on the hunt for the tree-dwelling cicadas. Locating one, she will deliver a sting which paralyzes the hapless cicada. Given the size of the cicada relative to the wasp, I find it amazing that the cicada killer is able to fly back to the burrow carrying its inert victim. Into one of the side chambers, she will drag the paralyzed cicada.
In each chamber containing a cicada, or a few, the wasp lays an egg. The egg will soon hatch into a larva that looks like a grub. This larva will now begin to consume the paralyzed, defenseless cicada. Within a week, or slightly more, nothing will remain of the cicada but a hollow shell. After feeding, the larva develops into a cocooned pupa which will spend the winter in the burrow chamber and emerge as adult the following summer.
What a creepy manner of death! It reminds me of the poor human victims of the horrifying, xenomorphic aliens in the movie series of that name. But alas, I am likely being a little too emotional.
The natural world can be harsh, of this we are all well aware. The 19th century practitioners of natural theology found predation and parasitism perplexing. How could a compassionate Creator allow such cold-blooded, merciless death to exist in nature they debated?
It became the lot of Charles Darwin and Alfred Russel Wallace to explain. Driven by natural selection (and much more, we now know), organisms diversify over time to fill, what seems to be, every imaginable ecological niche. Nature is not biased toward unkindness any more than She is geared toward benevolence. Perhaps Jurassic Park’s Dr. Ian Malcolm summarized it most simply. Said he, life will find a way.
Photo Credits: cicada killer wasp Alejandro Santilana at commonswikimedia.org annual cicada Insect Unlimited U. of Texas@commonswikimedia.org cicada killer with cicada Judy Gallagher at commonswikimedia.org