Researchers Discover Unknown Beetle Species Just Steps From Their Lab

A newly discovered beetle on campus has led to the first major update in Japanese ladybird classification in 50 years.

A routine look at a campus pine tree has led to an unexpected scientific discovery. At Kyushu University in Japan, researchers have identified a previously unknown species of ladybird beetle living in plain sight, underscoring how much biodiversity can still go unnoticed, even in familiar places.

The species, named Parastethorus pinicola, was found on Japanese black pine trees at the university’s Hakozaki Satellite campus. Despite decades of insect research in Japan, this tiny beetle had escaped attention until now.

The finding, reported in Acta Entomologica Musei Nationalis Pragae, emerged from a three-year investigation focused on revising the classification of the tribe Stethorini, a group of very small ladybirds that feed on spider mites. This work represents the first comprehensive update of this group in Japan in more than 50 years.

“I knew that this group of ladybirds often inhabits pine trees. Since there are Japanese black pines growing at the Hakozaki Satellite, I decided to look there, and that is where I found the new species,” explains Ryōta Seki, a PhD student at the Entomological Laboratory, Graduate School of Bioresource and Bioenvironment Sciences, and the first author of the study. “Normally, insect collectors do not pay much attention to pine trees, which is perhaps why scientists have overlooked this species for so long.”

The species, Parastethorus pinicola, takes its name from its association with pine habitats and is extremely small. The beetle measures just over one millimeter in length and appears as a tiny black insect that can be easily missed in the field.

Researchers at Kyushu University discovered a new ladybird beetle species, Parastethorus pinicola, on a pine tree at their Hakozaki Satellite. The finding was part of a major taxonomic review of the tribe Stethorini in Japan involving 1,700 specimens. The study describes two new species and corrects long-standing classification errors, proving that unknown biodiversity can still be found in the middle of a city—even on a university campus. Credit: Kyushu University/ Alfredo Javier (Pidot)

Discovery drives classification overhaul

“Small black ladybirds like these have not been studied much because they are incredibly difficult to identify,” says Seki. “They are barely larger than a grain of sand, and they all look identical. You cannot tell the species apart without dissecting them and examining their reproductive organs under a microscope. Because of this difficulty, there were many misidentifications in past records.”

In order to address these classification challenges, the researchers analyzed around 1,700 specimens. Their detailed examination revealed that the species commonly referred to in Japan as Stethorus japonicus is in fact the same as Stethorus siphonulus, a species found across a wide geographic range from China to Southeast Asia.

Microscopic traits obscure species boundaries

During the course of the review, the team also identified another previously unrecognized species from Hokkaido, which they named Stethorus takakoae. Seki chose this name in honor of his grandmother, Takako Ōtsuki, acknowledging her long-standing encouragement of his interest in entomology.

“Standardizing these names is important because it allows us to share data and research with other countries in Asia,” Seki notes. “It clarifies that this is a widespread species found from the tropics to temperate Japan.”

Hidden biodiversity reshapes understanding

For Associate Professor Munetoshi Maruyama of the Kyushu University Museum, who supervised the research, the findings point to how much remains undiscovered even in everyday environments.

“People rarely notice such small insects. But as our study showed, even in a city or on a university campus, there are unknown species living right beside us,” says Maruyama. “These ‘minor’ insects support our ecosystems. I hope this discovery makes people interested in the diverse and fascinating world that exists unnoticed at our feet.”

Reference: “Review of the genera Stethorus and Parastethorus from Japan (Coleoptera: Coccinellidae)” by Ryota Seki, Munetoshi Maruyama, 7 November 2025, Acta Entomologica Musei Nationalis Pragae.
DOI: 10.37520/aemnp.2025.021

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