Preparing for the Swarm: A Crash Course in Cicada Biology

 

Curious, clumsy insect swarm emerges like clockwork every 17 years.

Right now, an entomological phenomenon nearly two decades in the making is poised to explode! You may have heard the buzz (pun 100% intended) surrounding this year’s “Brood X” cicada, emerging from underground for the first time in 17 years. Before these insects start deafening us with their drone, here is what you should know.

The cicada that we are used to seeing year-to-year are referred to as “annual” cicada. These large, ungainly insects are typically 4-5 cm (1.5 – 2 inches) long and with green, tan, or brown bodies, and large clear wings. They are often called the “dog day” cicada for their emergence in the hot months of the late summer. Males advertise their positions to females by vibrating a specialized organ called a tymbal that is located on the underside of their abdomen, producing the cicada’s characteristic sound. Their loud drone is nearly synonymous with summer in many cultures.

 

 

Like waking from a long, dark slumber.

Brood X, however, are a different type of cicada. They are referred as “periodical” cicada, or sometimes by their genus name, Magicicada. The periodical cicada may have either 13 or 17 year long life cycles, depending on their species. The vast majority of this time is spent living underground as nymphs (immatures). Cicada nymphs feed off the fluids of tree roots using their straw-like piercing/sucking mouthparts. They rarely cause significant damage to a tree. In fact, cicada nymphs specialize in keeping a low profile. They are usually located around 2.5 m underground (about 8 feet), and slowly feed as they develop through five instars (molts). The fifth instar nymph digs a tunnel up to the surface where they go through their final molt and emerge as adults, leaving their exuviae (shed exoskeletons) behind.

Periodical cicada are smaller than our annual cicada, with body sizes maxing out at about 2.5 cm (1 inch). Their appearance is rather different as well, sporting black bodies and orange wings. Broods of periodical cicada denoted from one another by roman numerals (so brood X is brood 10). The next brood to emerge after this one will be Brood XIII in Illinois, Iowa, Wisconsin, and the southern reaches of Michigan in 2024. Brood X will emerge throughout Regions of Pennsylvania, Delaware, Maryland, Indiana, and Illinois; as well as a smaller emergence in Tennessee and North Carolina. When these insects emerge, they will do so in force. Brood X is by far the largest brood of periodical cicada in terms of numbers. The total emergence across all states will likely total in the billions, and possibly trillions of insects.

 

 

So why does this insect emerge in such ridiculous numbers?

It is actually a very clever defense mechanism. It should not be a surprise for most to learn that insects are very low on the food chain. Cicada are large and are very clumsy fliers. They are practically carrying around giant “Eat me!” signs for any predator with a taste for insects. To combat this, the periodical cicada emerge in overwhelming numbers, giving the predators just what they want — an easy meal.

This concept is called “predator satiation.” By emerging in titanic numbers, the cicada can ensure that the majority of the brood will be able to survive and reproduce. Predators, in return, gorge themselves on the insects, leaving little room for seconds. Essentially, for cicada, survival is a numbers game. And the odds are in their favor.

Additionally, the poetic drone of the annual cicada becomes an outright cacophony with the periodical cicada. A male cicada’s drone carries far. It is a very effective advertisement for attracting mates. However, it is a very effective advertisement for attracting the attention of predators too. When millions of the insect are all calling at once, it becomes next to impossible for a predator to pick out an individual insect’s call. This is a similar tactic to why small ocean fish form “bait balls” to protect themselves from large predators. The chances of any individual animal being picked off is very low. Strength in numbers, in this instance, is a ridiculous understatement.

 

 

There’s nothing to be afraid of…

Okay, so this is pretty spectacular, and possibly horrifying if you are entomophobic (or, afraid of bugs). But do we actually have anything to worry about? The short answer to that question is a resounding no.

Cicada do not bite and pose little to no danger to our crops, ornamental plants, or pets. They can certainly be annoying when they manage to stumble their way into a dwelling. Sure, you might have to brush one, or two, or quite a few of the insects (or their discarded exuviae) off of your house, or car. And you may come to find their piercing drone a bit annoying, but that is about it.

The large, ungainly Periodical Cicada only stick around for a short period of time — they will likely be gone before Labor Day. And in such numbers, pesticides are next to pointless. You would only be risking the health of non-target insects in doing so. Instead, do your best to enjoy a truly incredible natural event, and possibly start planning your 2038 vacation, if you’re not a fan!