(New Scientist) A widespread resurrection, orgies on a biblical scale, and births and deaths numbering in the billions will all soon be on display in the eastern US as a uniquely enormous population of insects known as 17-year cicadas bubble up from the ground. As their name suggests, these insects are famous for emerging from their subterranean nurseries on a predictable, but oddly-spaced schedule. Some species have a 13-year life cycle, others appear every 17-years.
Different broods of the insects emerge almost every year in some part of the US. But 2004’s crop of red-eyed, winged insects, ominously referred to as Brood X, is special, says Michael Schauff of the Agricultural Research Service’s Systematic Entomology Laboratory in Beltsville, Maryland.
“Brood X is the largest single emergence of the species,” he says. “When they come out they are literally everywhere. It’s impossible to ignore.”
This huge generation of cicada nymphs will begin to emerge in earnest by mid-May. They were spawned in 1987. They push out of the soil, forming tiny dirt mounds at the base of trees, and then literally crawl out of their juvenile skins.
What follows is a frenzied few weeks of feasting off plants, mating, egg laying and death. But before the end of the summer, the next generation will settled in for their very long dirt nap.
It has long been a mystery how cicadas mark time without any reference to the Sun or other seasonal signals. The current leading theory was developed by Richard Karban’s team at the University of California at Davis. His experiments suggest that cicadas somehow count the yearly surges of nutrients in roots that they suckle on in their underground lairs (New Scientist print edition, 16 September 2000).
Once the appropriate year rolls around for their revival, the slight warming of the soil probably tells them spring has sprung and drives them to the surface. Scientists are now using genetic tools to try to understand how the cicada clock works on a molecular level.
Males of the species call out to their mates with an infamous love song that to human ears is as sexy and sometimes as loud as a lawn mower ripping through tall grass. The 17-year cicada also endears itself to humans by making backyards uninhabitable, pelting windshields and clogging machinery. But the insects do little actual damage to crops or people.
The imminent burst of cicadas has triggered a burst of research. For example, Mike Raupp’s team at the University of Maryland, College Park, are planning to study how the sudden appearance of so many tasty treats affects aquatic ecosystems, how cicadas choose trees to snack on and methods to prevent cicada damage to young plants.
There also remains the mystery of why these creatures evolved such an odd lifestyle. Schauff endorses the idea that such an extended life cycle gives them an edge over predators at the surface which breed on an annual or more frequent schedule .
He points out that the enormous size of the brood also is an effective adaptation. “Their predators, such as small birds and mice, get so full of cicadas, they literally can’t eat any more. They are just overwhelmed.”
Even a few human cicada connoisseurs take the opportunity to sample a buggy buffet. Most popular are the animals who have just moulted from their underground skins. “They are quite soft and take on the flavour of whatever you cook them in,” Schauff reports. “They are not quite like a piece of meat, more like a small white potato that’s been cooked.”