May beetles

When the first rain showers of the year begin, the May beetles appear. These insects from the Phyllophaga genre emerge from the ground to mate and reproduce.

There are around 70 species of May beetles in Costa Rica. In general terms, they have longer legs that make them look clumsy when they walk outside of their natural habitat.
Most of these beetles measure between 1 and 1,5 centimeters in length.

People talk about May beetles mostly in the Central Valley and the North Pacific area of Costa Rica, because that’s the month when rain showers begin. In the South Pacific, these beetles emerge earlier in April, while in the Atlantic, since it rains constantly, there is not such a strong link between their life cycle and the weather.

When the first rain showers occur, the adult beetles come out of the ground to mate and reproduce. The female beetles stay on leaves or tree branches, while the males flutter around them, attracted by fermones (chemical active substances) that the females emit.

On occasions, it is possible to see thousands of beetles flying simultaneously 60 or 70 centimeters above the ground.

Once copulation takes place, the female buries herself in the ground and lays her eggs in the already humid soil. A few days later, the larva comes out and starts to feed mostly on plant roots.

Towards the end of the rainy season, these larvae turn into pupas and then into adults. These adults remain inactive under the ground, inside a cell, until it starts to rain again.

Source: Ángel Solís, biologist at INBio