One doesn’t have to live in the Arizona desert long to learn that once the first cicadas of the year start broadcasting their piercing buzz from invisible locations in the trees, it’s time to kiss spring goodbye and say hello to the blast furnace that is June in much of the state.
University of Arizona News talked with Gene Hall, manager of the University of Arizona Insect Collection, about cicadas and what makes them so unique.
1. Cicadas stay underground for years and can emerge en masse.
Cicadas have made national headlines this year, appearing in massive numbers almost overnight in some parts of the eastern U.S. Meanwhile, Arizonans have yet to hear them.
“Cicada life cycles can range from three years for our local species to up to 17 years for those in the Midwest and eastern United States,” Hall says. “It is thought that these mass emergence events that you have seen in the news may have evolved as a strategy to deal with predators. I have read about estimates that some places see a million or so cicadas emerge per acre. And when you’ve got such large numbers of individual cicadas out, there’s just no way predators can keep up with that. It’s like survival by numbers in a way.”
“In the species we have around here (in Tucson), the underground stage lasts anywhere from a couple to three to five years,” Hall says. “We don’t have the big brooding cycles like periodical cicadas, and a reason for that might be that here in the Southwest, they can avoid predators simply by being out during the hottest part of the day, when nobody else can or wants to. Animals that otherwise would go after them, like lizards, birds and mammals, are trying to stay out of the heat.”
2. Built-in air con: Cicadas can turn themselves into an evaporative cooler.
Why are cicadas active during the hottest part of the day?
“Because they can,” Hall says. “Cicadas have figured out a way of sweating, if you will. They feed on plant sap, so they are constantly sucking in liquids, and as the temperature gets hotter and hotter, and they start to overheat, they remove the water from their blood and pass it through ducts in their body. As it exits their body through pores on their thorax, they get that continuous evaporative cooling. When people talk about how it seems like it just feels hotter when they hear the cicadas, that’s because they’re out when it is hot. That trick allows them to be active when it’s too hot for the predators that feed on them. Many reptiles and birds and mammals that would normally go after them seek shelter from the heat when it gets to be 110 degrees or more, but cicadas can still be active and feeding and sending out mating calls.”
3. Cicadas build stuff underground.
“The adult female lays her eggs into twigs,” Hall says. “When the eggs hatch, an immature stage – called a nymph –falls onto the ground, where it will then burrow. The nymph lives underground and feeds on plant roots with its piercing-sucking mouth parts, moving along chambers and tunnels that it digs with its strong, clawlike front legs. When it’s ready to molt into an adult, the nymph crawls out of the ground and looks for a surface to cling to, like the base of a tree or a building. It will then shed its final nymphal skin. The newly emerged adult will be pale and soft-bodied until the exoskeleton hardens, and then proceeds to live the remainder of its life. Like the nymphs, the adults possess piercing-sucking mouthparts and are plant feeders.”
4. Cicadas can make their own armor overnight.
Scientists believe nymphs emerge from underground when certain environmental cues fall into place and the conditions become just right –for example, as soon as the ground reaches a certain temperature, Hall says.
“They emerge usually in the evenings or at night, and the next day you might find their nymphal skin where they’ve emerged from,” he says. “They’re very vulnerable when they emerge, because the body of the adult starts out soft. It takes a while to harden up and for the wings to fully push out and develop. It probably takes a few hours. It can’t be too long because they have to be active the next morning. The adult lives only for two to three weeks, which is kind of typical for most insects.”
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