In many regions of Costa Rica, the arrival of May beetles once heralded the start of the rainy season. These nocturnal beetles, also known as Phyllophaga spp., have been part of the Costa Rican landscape for generations. Their presence was not only symbolic but also ecologically significant. However, in recent years, scientists, farmers, and citizens have noticed a concerning decline in their populations.

The decline of May beetles is not just a biological phenomenon; it is an alarming symptom of the broader environmental deterioration the country is facing. In this article, we explore the history of these insects, the factors behind their disappearance, and what is being done—or could be done—to reverse this trend.

History and Ecological Role of May Beetles

May beetles belong to the family Scarabaeidae, a group of beetles with over 30,000 species worldwide. In Costa Rica, their presence has been prominent since pre-Columbian times, especially between April and June, when they emerge massively at night.

For decades, they were considered seasonal indicators. Their appearance coincided with the start of the rains and the blooming of many crops. They also serve as a key food source for animals such as insectivorous birds, opossums, bats, frogs, and even some reptiles.

At ground level, their larvae help aerate the soil and decompose organic matter, playing a vital role in soil fertility. Therefore, their role within the ecosystem is more complex and significant than previously thought.

Habitat and Population Decline: Multiple Causes

1. Uncontrolled Urbanization

The expansion of urban areas has drastically transformed many natural habitats where these beetles lay their eggs. The loss of vegetation cover, the increase in concrete surfaces, and nighttime artificial lighting have interfered with their reproductive and migratory cycles.

2. Intensive Pesticide Use

Costa Rica’s agricultural model, focused on monocultures like banana, pineapple, and coffee, has led to increased use of agrochemicals that not only kill pests but also non-target species such as May beetles. Pesticides affect both adults and larvae in the soil.

3. Climate Change

Changes in rainfall and temperature patterns have also had a negative impact. The synchronization between the emergence of adults and optimal environmental conditions is breaking down, preventing the species’ successful reproduction.

4. Light Pollution

May beetles are highly phototactic, meaning they are attracted to light. Increased urban lighting can disorient them, diverting them from breeding sites and making them vulnerable to predators or death by exhaustion.

Environmental Consequences

The progressive disappearance of May beetles creates an ecological cascade effect. Some consequences include:

• Reduced food availability for insectivorous species, affecting their reproduction and survival.
• Disruption of the food chain, altering biodiversity.
• Decreased soil aeration and organic matter decomposition, leading to lower soil quality.
• Negative impacts on pollinators, since many nocturnal species interact indirectly with plants and flowers, affecting reproductive processes.

In short, their decline affects dependent species and the overall health of Costa Rica’s ecosystems.

Conservation Initiatives and Efforts

Research and Monitoring

Biologists from institutions such as the University of Costa Rica (UCR) and the National Institute of Biodiversity (INBio) have begun monitoring their populations and changes in their distribution. This research is key to better understanding their life cycle and the threats they face.

Environmental Education

Organizations like Fundecor, Tropica Verde, and community projects in Sarapiquí and Guanacaste are promoting awareness campaigns for children and young people about the importance of these insects.

Good Agricultural Practices

Some ecological farms have opted to minimize pesticide use, implement vegetative barriers, and promote biological corridors that help preserve safe habitats for native species, including May beetles.

Citizen Participation

Spotting May beetles has become a community activity in certain regions. Citizens are using apps like iNaturalist to record and report sightings, contributing to databases that help scientists track their presence and evolution.

What Can We Do as Individuals?

• Reduce unnecessary outdoor lighting from April to June.
• Avoid the use of broad-spectrum insecticides in gardens and homes.
• Participate in citizen science projects that monitor biodiversity.
• Plant native species in gardens and green spaces to provide habitat and food.
• Educate others about their importance and promote a culture of respect for insects and their role in ecosystems.

Conclusion

The decline of May beetles is not an isolated event, but a warning sign about the health of our ecosystems. These insects, though small and often overlooked, are essential to the natural functioning of Costa Rica’s environment.

Protecting them means protecting biodiversity, soil balance, and the country’s ecological heritage. From individual actions to public and corporate policies, every effort counts.

Costa Rica, internationally recognized for its leadership in conservation, now has the opportunity to also lead in the protection of small but vital species such as May beetles.