Why in news
Two broods of periodical cicadas (Brood XIX and Brood XIII) are emerging in the U.S. after 13-17 years, marking the first time in 200 years they’ve appeared together.
This coincides with the emergence of Australian greengrocer cicadas, which have a seven-year life cycle.
The overlapping emergence of these cicadas raises questions about the mathematical patterns behind their life cycles and survival strategies.
Cicada
Cicadas are insects that belong to the order Hemiptera and the superfamily Cicadoidea.
Hemipteran insects, also called true bugs, have mouthparts used for piercing and sucking and have two pairs of wings.
They spend most of their lives underground and emerge from the soil mainly to mate.
Once out of the ground, their life span is fairly short, somewhere between two to four weeks.
Most cicadas are canopy dwellers and are found in natural forests with large trees; found in every continent except Antarctica.
The genetic diversity of cicadas in India and Bangladesh ranks the highest globally, followed by China.
The adult cicadas are vulnerable to predators such as turtles and other forest inhabitants because they are clumsy and lack defences, making them virtually easy prey.
Cicada Life Cycles
Cicadas have complex life cycles that involve long periods of underground development and short periods of adult emergence.
Cicadas have life cycles that last 13 or 17 years, which are prime numbers.
There are three species of cicadas that emerge every 17 years and three species that emerge every 13 years.
This prime-numbered cycle helps them avoid predators with predictable life cycles (e.g., those with 2, 3, 4, 5, 6, or 7-year cycles).
By emerging at prime-number intervals, cicadas minimize overlap with predators, maximizing their chances of survival.
The overlap between cicadas and predators is calculated using the "lowest common multiple" (LCM) of their life cycles.
Originally, 30 broods of periodical cicadas were categorised based on geography and emergence times, but currently, only about 15 broods remain active due to some becoming extinct.
COMMENTS