This post was originally made on Facebook on June 7, 2016. I transferred it to this blog three years later on June 7, 2019 and added additional images to illustrate why cicadas are such interesting insects.
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There are a lot of desert cicadas out here this year, more than I’ve seen at least since I moved to the property 4 years ago. These large and scary-looking but harmless insects spend 2 to 5 years underground as grubs feeding upon plant roots before emerging as winged adults. The adults live for only a few weeks, during which time they must mate and lay eggs for the next generation.

Desert cicadas (genus Magicicada, containing about 20-25 desert species) appear in the last few days of May or the first week of June in the Sonoran and Mojave Deserts, and are evident for less than four weeks before they complete their mating and egg-laying. They then disappear from view for the next 11-plus months, living entirely underground as nymphs feeding upon plant roots.

One notable feature of desert cicadas is the fact that they are most active during the hottest parts of the sunniest days at the driest times of early summer. Why would this be? It is thought that evolution equipped these insects to be active at a time when most of their predators are unable to function due to the drought and high temperatures. Their breeding calls are very noisy, they are conspicuously large (although many are quite cryptically camouflaged), and they are nontoxic and cannot bite or sting in self-defense. All of this makes them desirable and relatively easy-to-capture prey for birds, kit foxes, lizards, and whatever else would enjoy them for a snack. So to avoid being eaten, desert cicadas have evolved to be active when little else is, at the most inhospitable time of the day when everything else seeks shade and rests to conserve water and energy.

Magicicada sp on a palo cristi tree (Canotia holacantha) in western Arizona in June 2015.

There is one more fascinating fact about desert cicadas: They sweat, just like we humans do! Sweating is an adaptation that allows us to be active in hot weather, run long distances, and work hard without overheating. Very few animals can sweat to cool themselves off, and as long as people have an adequate intake of water it is an extremely effective system for us to regulate our internal temperatures on hot days in tropical and subtropical climates. This is why dogs, horses, and many other creatures can easily suffer from heat exhaustion when running in hot weather while humans can just keep going as long as they have water to drink and can pour out sweat liberally. Most four-legged animals can outrun humans in terms of speed, but in warm situations they cannot out-endure us. Since they cannot sweat they overheat and collapse.

Well arid-land cicadas are the same in this regard, and they are the only insect with a system of pores that enables them to transfer water from their blood to the surface of their thorax to evaporate into the air, thereby cooling themselves off. While effective to cool the cicada on a torrid afternoon, it represents a huge water loss every day which could quickly be fatal if not continually replenished. So where does the replacement water come from? Cicadas have specialized mouthparts that are designed to pierce directly into the water-carrying xylem tissues of vascular plants, and they simply sink a straw into the plant to withdraw the water they need just as humans drink from a tap. So with a plant-based water supply, sweat pores, and the ecological imperative to be active to avoid predators in the heat of high noon, desert cicadas can successfully survive and thrive at mid-day in this harsh habitat. Ingenious!

Interestingly, cicada species from wetter and more humid climates where evaporative cooling is much less effective lack these sweat pores. They just aren’t useful there and therefore didn’t evolve. That, combined with more vegetation to hide in, means that many cicadas from the tropics and forested temperate regions are nocturnal rather than diurnal. This is one more intriguing example of how the environment that animals live in over time shapes their evolutionary adaptations.

Details of the compound eyes and wing venation of a desert cicada.

The shrill calls they emit can be up to 120 decibels in loudness, so being around one at close range can be deafening. Also, look at the beautiful compound eyes and the large, transparent glassy wings on this two-inch-long bug. What a marvelous little beast!

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A couple of my friends made comments and added photos of cicadas of their own, which I will add here for posterity.

Owen reports: “Ohio is currently dealing with 17 year (I think) cicadas. It’s been horrible the last couple weeks. They’re harmless but annoying. Luckily, they’ll be gone soon enough although the smell from all the dead ones is already pretty bad.”

“This is pretty much what it looks like everywhere you go around here. I was outside over the weekend & have had many of them run into me. I almost feel bad for them because they seem so dumb & clumsy ha-ha.”

Fascinating photos Owen! I’d heard that there was an outbreak of these this year (June 2016) in some places. It seems that every year, somewhere in the eastern US, a large cyclical hatch of 17 year cicadas happens over a large region, creating the nuisances of noise and mess and stench of dead bugs that you showed. There are some cicadas every year, so not every individual insect is in sync with the major hatches, but these 17 year cyclical outbreaks can be predicted from the historical record. It’s Ohio’s turn. On to Virginia in 2017!

Leia reports: “I posted shots of our cactus dodger cicadas today too. Love them. Such fascinating guys.” This is probably the same species of cicada I posted, since Leia lives in my region about 50 miles away from me.

It is interesting to note that the periodical (aka cyclical) cicadas, which have life cycles of either 13 or 17 years, are all from more humid climates, while these desert species are non-cyclical. This means that our desert and western USA species do not go through population booms every 13 or 17 years, and are instead present in low or modest numbers every year. Their life cycle of 2 to 5 years is markedly shorter as well, although still rather long when compared to most other insect types. These western species are the ones that have adapted to sweat, since they emerge and are active at the hottest, driest time of year in mid-day; therefore sweating enables them to conduct their life when predators must avoid the heat, as discussed above. The periodical cicadas of the humid eastern climates are not able to sweat, and while many can be heard in the middle of a sunny day there are also nocturnal species, which call at night, which the western ones never do.

Cicadas are not just biologically interesting, but they are beautiful in a subdued way. I like the refractive effects of the compound eyes, which we also see in other insects like dragonflies and bees. Some tropical species are much more colorful, but the desert ones need to be muted in color so that they don’t draw the attention of predators to themselves.