The Longest Living Insects and their Periodical Emergence

In the world of insects, few creatures are as intriguing or as misunderstood as cicadas. Known for their deafening mating songs and their remarkably long life cycles, cicadas have fascinated scientists and laypeople alike for centuries. Despite their sometimes alarming appearance and overwhelming presence during their mass emergences, cicadas are harmless insects that play a unique role in their ecosystems.

This article explores the captivating life cycles, biology, and ecological impacts of these enigmatic insects.

Life Cycle and Biology: Defining Characteristics

Cicadas are most famous for their long and distinctive life cycles. While most insects have life cycles lasting from a few weeks to a couple of years, cicadas live far longer. Some species, known as periodical cicadas, spend 13 or 17 years underground as nymphs, feeding on tree roots and slowly growing. After this extended juvenile period, they emerge from the ground en masse, molt into their adult form, mate, lay eggs, and then die, all within a few weeks. This coordinated, periodical emergence of adult cicadas is unique in the insect world.

This periodicity is not present in all cicada species. Annual cicadas, which are more common and widespread, have life cycles that last 2 to 5 years. These cicadas emerge every year because their life cycles are staggered, creating the impression that they are 'annual'.

The reasons for the long developmental period and the periodical emergence of certain cicada species have been subjects of extensive research. The prime-numbered life cycles (13 and 17 years) of periodical cicadas are thought to be an evolutionary response to avoid syncing up with the life cycles of predators and to prevent hybridization between broods.

When the time comes for adult cicadas to emerge, they do so simultaneously, in numbers reaching up to 1.5 million per acre. This strategy, known as predator satiation, ensures that even though many individuals will be eaten by predators, enough will survive to reproduce successfully.

The Ecological Role of Cicadas

Cicadas play several important roles in their ecosystems. During their growth phase, cicada nymphs aerate soil and contribute to nutrient cycling by feeding on tree sap and excreting a nutrient-rich substance. Their mass emergence provides a significant food source for a wide range of predators, and the sudden death of adult cicadas delivers an influx of nutrients to the soil, supporting plant growth.

Cicadas also influence the structure of their communities in more subtle ways. For instance, their feeding on tree roots during their nymph stage can cause significant damage to young trees, affecting forest succession. The mass emergence of adults can also cause noticeable, though usually short-term, damage to vegetation.

Human-Cicada Interactions: From Irritation to Inspiration

Human reactions to cicada emergences vary widely. Some people regard the loud, mass emergence of cicadas as a nuisance, while others see it as a wonder of nature. Despite their alarming appearance and overwhelming numbers, cicadas are harmless to humans. They do not sting or bite, and their feeding habits do not significantly harm mature trees.

Cicadas have influenced human culture in surprising ways. They have appeared in literature and folklore around the world as symbols of rebirth or immortality, thanks to their long lifespans and their dramatic re-emergence from the ground. In some cultures, cicadas are even collected as pets or consumed as food, valued for their nutritional content.

Future Research and Conservation

While much is known about cicadas, they still hold many mysteries. Scientists are still learning about their physiology, their behavior, and the exact environmental cues that trigger their emergence. Climate change poses new questions and threats, as changing temperatures may affect cicada life cycles and distributions.

Despite their occasional reputation as pests, cicadas are an integral part of their ecosystems and are generally not a target for pest control. However, habitat destruction and climate change pose significant threats to these fascinating insects.

As we discover, cicadas are truly remarkable insects, with their long lives, their synchronized emergences, and their significant impact on their ecosystems. Their unique life strategies have much to teach us about evolution, ecology, and the incredible diversity of life.