Heatwave Silences Cicadas: Unusual Silence Hits Insect World

Their song, a true soundtrack to sunny vacations, usually sets the rhythm for summer days. However, recently, a heavy silence has descended over the Mediterranean. « It’s unsettling », says Brigitte, a resident of Nîmes, to Decatur Metro. « Since the end of July, I no longer hear the cicadas where usually they are so loud that we can hardly hear ourselves speak. » In her shaded neighborhood, the males, perched on maritime pines, typically vibrate their abdomens during the hottest hours, hoping to attract females. This phenomenon is reported in several southern cities, according to local media.

The same observation comes from Aix-en-Provence. On August 12, « it was a symphony », recounts Marguerite from her balcony in the town. But, from the next day, as temperatures approached 40°C and three quarters of France were under a heatwave alert, « it was completely quiet », she marvels. This has been happening since August 8, as France struggles with another heatwave, following the unusually early and lengthy one in June: sixteen days.

According to science communicator Léo Salel, extreme temperatures impact the life cycle of cicadas. This insect expert also notes their absence in the southern Ardèche this August. He suggests, « with increasingly dry and hot springs, it’s possible that cicadas, which are thermophilic species dependent on external temperatures to emerge from the ground, start singing earlier and thus end their adult cycle more quickly ».

This analysis aligns with that of Serge Zaka, an agroclimatologist based near Montpellier: « The optimal temperature range for their activity in the open air is between 22°C and 37°C, depending on the species. Thus, with climate change, we expect them to start singing earlier. » In August 2022, he already observed that cicadas stopped singing by mid-July in the north of Montpellier.

Some experts are reassuring. « There’s no need to worry. If they stop singing, it’s because they have completed their reproductive cycle », states Stéphane Puissant, an entomologist and cicada specialist at the Museum of Natural History in Dijon.

Cicadas spend most of their lives underground, undergoing five molts before emerging, wings unfurled, in a final transformation. In France, 22 species are recorded, the most famous being the gray cicada (Cicada orni), which can live buried between 2 and 6 years. Even from the same clutch, larvae do not all emerge at the same time, explaining variations in abundance that are difficult to interpret. « The phenomenon may be related to conditions that occurred during egg-laying, several years earlier », explains Jean-Laurent Hentz, a naturalist based in Beaucaire (Gard).

Before dying, the females lay eggs inside the stems of plants. One to two months later, the larvae burrow underground for a period ranging from a few years to several decades, depending on the species. Their lifespan above ground, corresponding to the adult and reproductive stage, lasts only 1 to 2 weeks. During this brief period, only the males produce their song, ranging from ultrasound, inaudible to the human ear, to cymbalizations that can reach 90 decibels, equivalent to the noise of a chainsaw.

In France, few studies document the effects of climate change on cicadas. « We need more perspective », explains Stéphane Puissant, who studies species with exceptionally long life cycles in the United States and Mexico. « These are species that have evolved over millions of years, and some of them can live underground for twenty years. Even though we have data from the last thirty years, it will take several more decades to confirm the observed trends. » To date, 3,400 species of cicadas have been identified worldwide.

Abroad, some research already offers insights. A Japanese study on endemic species, for instance, has found that as temperatures rise, cicadas reach sexual maturity earlier.

Another phenomenon is emerging in France: their singing schedules are changing. Now, they mostly sing in the morning and evening. « In the afternoon, it’s silent: no birds, no cicadas, emphasizes Serge Zaka. With the heatwave, entire ecosystems are suffering. The cicada is just the tip of the iceberg because we hear it, but we must not forget the others. »

Some cicada species have developed remarkable adaptation capabilities. Those from the Algerian-Moroccan desert manage to sing even at 36°C in the shade, explains Stéphane Puissant. Thanks to their underground life, they adjust their emergence based on the external conditions that are optimal for them. « As long as their food source — the roots of trees and shrubs from which they suck the sap — remains available, they are not necessarily threatened », the researcher specifies.

This resilience is not shared by all insects. « The main causes of insect disappearance, therefore of cicadas, are intensive agriculture and the artificialization of soils, says to Decatur Metro Stéphane Jaulin, an entomologist at the Office for Insects and their Environment. But, for the past 4 or 5 years, I am convinced, it is climate change that is taking over. »

Data from the National Museum of Natural History, derived from a synthesis of European studies, confirms the trend: insect populations have dropped by 70 to 80 % in European landscapes. Few studies specifically concern cicadas: in the absence of economic consequences and damage to crops, funding to study them is limited, notes Serge Zaka.

As early as 1995, entomologist Michel Boulard was alerting in his reference book Vies et mémoires de cigales about the sudden disappearance of certain species, like Tibicina tomentosa. Once very common in southern France, it has become extremely rare due to the expansion of vineyards, « great devourers of garrigue ».