The reemergence of Brood X – Curiosity or Calamity?

If you live in the Eastern United States you are likely aware of the coming emergence of “Brood X”, the largest brood of periodical cicadas in existence. This family of flying insects (Magicicada septendecim) are often referred to as “Pharaoh cicadas” or “17-year locusts”, referencing their incredible 17-year lifecycle. Indeed, once every 17 years the members of brood X emerge from the ground and swarm across 15 states in a biologically unique event. While many people alternate between fear, disgust, and exasperation, the reemergence of the cicadas can also be a fascinating event!

Cicadas are members of Hemiptera, a large group of insects comprising over 80,000 species. There are approximately 3,000 distinct cicada species, most of which have an annual lifecycle. They hatch from eggs laid in tree branches, drop to the ground and burrow into the soil, and spend the next year feeding on small roots and growing before they emerge as adults. The adult cicadas typically only live 2 to 4 weeks, during which time they mate, lay eggs, and die. But, unlike the annual cicada species, there are seven species that have evolved to have an extended nymph phase, long lifespan, and synchronized emergence after either 13 or 17 years. For the past 17 years, the Brood X cicadas have been burrowing underground and developing, but over the next month they will begin to tunnel upwards before emerging in May and June.

Emergent swarm of Brood X from 2004. Photo by Greg Hume, CC BY-SA 3.0

It’s hard to understate the magnitude of the Brood X emergence. Across the region where they live (check out this amazing map from the University of Connecticut to see exactly where they are emerging!), trillions of cicadas will emerge, with the most populated areas having upwards of 1.5 million cicadas per acre! As the cicadas swarm they will set about mating, producing a noise that can reach 100 decibels (as loud as a lawnmower or a low-flying aircraft). In addition, swarming cicadas can become a nuisance to anyone hoping to enjoy even a brief moment outside. They pelt you as you walk or ride a bike, swarm farm and lawn equipment (potentially mistaking the drone of a lawnmower for a mate), and make outdoor sports difficult. After just a few weeks the mighty swarm will begin to die off, leaving behind dead insects that litter roads, lawns, and waterways.

Despite these annoyances, the emergence of the Brood X cicadas is a biologically wonderful event. Animals will be treated to a feast unlike anything from the past 17 years. Birds, reptiles, spiders, rodents, and your household pets love to eat cicadas. They are quite delicious (so I’ve been told), so feel free to grab a few handfuls and fry them up! It is recommend to try to limit the amount that your family pets eat, but a few crunchy mouthfuls is unlikely to cause harm. Cicadas are also generally harmless – they do not bite or sting, and other than accidentally flying into you are unlikely to cause any harm. In addition, the piles of dead cicadas provide a source of nitrogen for growing plants!

Cicadas can cause damage trees while laying eggs, so experts recommend waiting until after the brood has died off before planting new trees. Mature trees often suffer minimal harm, but young trees should be covered in netting to prevent cicadas from landing. Importantly, adult cicadas do not eat leaves off of trees or other plants. Finally, burrowing cicadas can produce small exit holes as they emerge, but these will not harm lawns longterm and can actually help to aerate the soil. The most important thing is to avoid the use of pesticides – they are very unlikely to help control the cicada population, can kill other beneficial insects, and can leave residual harmful chemicals in your plants and soil.

Emergence holes underneath flagstone – Photo by Greg Hume, CC BY-SA 3.0

Regardless of your feelings (amazing biological phenomenon or disgusting insect plague) the cicadas will soon be emerging. There are many fascinating aspects to Brood X that you can explore in the classroom: why have the cicadas evolved to emerge on a 17-year cycle, why do bird populations actually seem to drop in large brood years but then rebound even higher the following year, and can you find local or regional accounts of past cicada broods in your area? Finally, encourage students to join others in a citizen scientist initiative to help track the cicadas – I will be using the Cicada Safari app to help map cicadas in Northern Virginia and Washington, D.C. Either way, I encourage you to try to enjoy the emergence for what it is – a potentially once-in-a-lifetime event that is not found anywhere else on the planet!

Header image: Jaydro on, CC BY-NC-ND 2.0

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