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PERIODICAL cicadas have long been renowned for their timekeeping. Now
researchers in California have found they鈥檝e been cheating.

After developing underground for 13 or 17 years, millions of cicadas in the
US emerge from their tree root nurseries, all within a few days. How they keep
track of time so accurately has long been a mystery.

鈥淐icadas live underground where light and temperature remain relatively
constant year round,鈥� says entomologist Richard Karban of the University of
California at Davis. So many biologists have assumed that the nymphs rely on
internal clocks, dead-reckoning their way through time.

Now a team led by Karban suggests that cicadas may cheat by counting the
flowering cycles of their host plants. The team removed 15-year-old nymphs of
the 17-year cicada Magicicada septendecim and transplanted them to
young peach trees.

One group was introduced to trees kept in a large growth chamber where day
lengths were artificially accelerated, tricking the trees into flowering twice
in one season. These cicadas emerged a full year early. Nymphs transplanted to
control trees that flowered only once鈥攍ike the nymphs left in the
wild鈥攁ll emerged on schedule.

Karban speculates that cicadas tick off the years by monitoring sap quality.
He points out that the nutritional content of sap changes seasonally, with amino
acid concentrations peaking when flowers open, for example. Other insects are
known to rely on seasonal changes to synchronise reproduction and hatching, he
says.

The finding strikes a chord with other researchers. 鈥淭he idea makes perfect
sense,鈥� said Alfried Vogler of the Natural History Museum in London. 鈥淭heir work
may add a beautiful study system for analysing the intriguing mechanisms of
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