First Beetles Emerge from 145 Larvae in Liepijų Forest

The first protected hermit beetles have emerged from specially installed nest boxes in Liepijų Forest, marking the first visible result since 145 larvae were moved there a year ago.

The larvae were raised by specialists at the Lithuanian Zoo before being transferred to the artificial habitats in Žemaitija National Park in Lithuania. Their emergence shows that conditions inside the boxes allowed at least some of them to complete their development and reach adulthood.

However, the announcement published by Lithuania’s State Service for Protected Areas does not say how many adult beetles have been recorded. It therefore remains unclear what proportion of the 145 larvae survived, emerged or are still developing.

Prepared by the infoerdve.lt editorial team using information from Žemaitija National Park. Published on 27 July 2026.

A single generation of the hermit beetle takes three to four years to develop. The insect spends most of its life as a larva, while an adult survives for only a few weeks during the summer.

This long life cycle means the project cannot be assessed on the basis of one season or the first adults to appear. Some of the transferred larvae may not yet have reached adulthood because individual development times can vary.

Even so, the emerging beetles provide direct evidence that at least part of the transferred group completed the larval stage successfully. Each adult could contribute to the species’ recovery, but only if the beetles find suitable natural habitat and reproduce.

The appearance of the first adults should therefore be viewed as an intermediate milestone rather than confirmation that a self-sustaining population has been established.

The conservation method used in Liepijų Forest is known as ex situ breeding. It involves breeding or raising a species outside its natural habitat and later transferring individuals into an environment where they may be able to survive independently.

The work forms part of the project “The Old Oak Route for the Hermit Beetle in Lithuania and Latvia.” The nest boxes give larvae a place to develop in the forest while suitable natural habitats are available nearby. They act as a transition between specialist-supervised rearing and life in the wild.

The objective is not to keep the beetles permanently in artificial boxes. The project is intended to help adults move into natural habitats, mate and produce another generation without human assistance.

Liepijų Forest was chosen because it contains many mature, hollow oak trees. Decaying wood accumulates inside these trees, creating the natural material in which hermit beetle larvae develop.

The protected species is regarded as an indicator of the condition of old broadleaf forests and habitats containing mature trees. Its presence is associated with environments where old trees, cavities, natural wood decay and biological diversity have been retained.

The project’s longer-term significance therefore depends on more than the number of beetles emerging from the boxes. The crucial question is whether the natural structure of Liepijų Forest can support their descendants.

The first adults confirm that the transfer produced a biological result. Their appearance alone, however, is not enough to demonstrate that a viable new population has formed. The beetles must still find appropriate hollow trees, reproduce and leave a new generation behind.

Because larval development can take up to four years, the forest’s potential as a permanent habitat will become clearer gradually. The strongest future evidence of success would not simply be more adults emerging from artificial boxes, but a new generation of larvae developing naturally inside the cavities of Liepijų Forest’s old oaks.

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