Abejones de Mayo, or May beetles (Phyllophaga spp.), have traditionally been so characteristic of the start of Costa Rica’s rainy season that there is even a popular saying, “clumsy as a May beetle,” to describe their erratic flight in the presence of artificial light.

But populations of the once-ubiquitous insects, also known as June bugs and July beetles elsewhere, appear to have cratered in recent years. “They used to swarm a single light bulb by the dozen, but it’s become apparent even to the general population that this phenomenon is a thing of the past,” says Andrés Arias, a biologist at the University of Costa Rica (UCR).

Also alarming, scientists have yet to explain the relatively sudden plight of the beetle, a key food source for animals ranging from birds and bats to frogs, armadillos and snakes.

“The population loss is so obvious that society is turning to academia to ask for explanations as to what’s happened to all the May beetles,” says Arias. “But we don’t have the facts. There are no studies.”

The lack of evidence spurred UCR scientists to publish an interview with Arias on the subject in the university’s newspaper on May 21.

May beetles, of which there are 430 species in Costa Rica alone, are the tip of a far larger iceberg, experts say. They point out that Latin America suffers from a dearth of quantitative insect studies—and, thus, a lack of data from which to make evidence-based policy decisions.

The beetles’ dwindling numbers are apparent elsewhere in the world. A 2020 study published by Insect Conservation and Diversity, a scientific journal of the UK-based Royal Entomological Society, reported a significant decline in beetles, moths and caddisflies studied in the Netherlands. The same year, the scientific journal Annual Review of Entomology published a study that recorded lower numbers of beetles generally, worldwide.

Array of possible causes

While acknowledging there is not much more than anecdotal local evidence of the disappearing May beetle, Arias, a specialist in insects, hypothesizes on causes that likely apply to May beetles.

Urbanization, he says, poses several challenges to the May beetle, which spends 95% of its one-to-two-year lifespan underground. When excavators move in to clear the way for construction, the May beetle is defenseless. Once urbanized, their existing habitat is more often turned over to concrete, leaving few options for future generations to lay their eggs in the ground.

“By comparison to evolution, the habitat loss spurred by construction is happening in the blink of an eye,” says Arias.

Artificial lighting that comes with urbanization, meanwhile, disorients insects by leading them to confuse it with light from the moon or stars, which they often use to guide them.

Climate change is another factor altering the lifecycle of the May beetle, given that reduced rains and increasingly intense droughts are very disruptive. The May beetle emerges from the ground when it senses the humidity at the start of the rainy season. It only spends 3-4 weeks of its life above ground, during which time it must mate. But if this crucial stage of the May beetle’s life is upset, the reproductive cycle may be broken.

Arias believes industrial pesticides are also causing the loss of the May beetle.

“The indiscriminate use of highly toxic pesticides combines with the atmospheric cycles, such as rain and evaporation,” he says, “and the pesticides end up spreading in an uncontrolled way beyond the crops they were intended to target and into all natural habitats.”

According to the UN Food and Agriculture Organization, Costa Rica is among the top five consumers of pesticides on a per-hectare basis in the world, along with the Bahamas, Saint Lucia, Colombia and Israel. The Regional Institute for Chemical Substances at the National University of Costa Rica found that 90% of the pesticides used in the country’s agricultural sector, in which bananas, pineapples, and coffee dominate, pose significant risk to humans and the environment.

Agronomist Javier Souza, coordinator of the Latin American arm of the nonprofit Pesticide Action Network (RAP-LA) says public attitudes play a part, too. “There is a general vision in Latin America that we need to do away with insects,” Souza says. “A reductionist, anthropocentric view that gives little importance to insects has permeated governments, the education system, the popular view and even the agriculture sector.”

But May beetles, like all insects, play a vital role in the ecosystem. They are important pollinators; a source of nutrition for birds, their main predators. They recycle nutrients, their excrement serving as fertilizer for the earth. The tunnels they create in the soil allow for air and water to circulate underground, which is critical for ecosystem health and agriculture.

“May beetles are allies that contribute to the health of the ecosystem,” Arias says. “This applies to most insects, each of which performs a unique function, like cog wheels in the delicate balance of a healthy environment.”

Arias says the void in research on May beetles cannot be filled in a hurry, even if copious funding were available for the purpose.

“Evolution is a long process, [and] we cannot expect quick results,” Arias adds. “Private and public institutions need to give more importance to natural history studies. Recently, the trend has been to focus funding on technical research, but natural history is the foundation to everything, and without this base we cannot make evidence-based decisions.”