Male Japanese stick insects have stopped participating in reproduction; females now handle everything on their own.

In order to reproduce, most animals require both a male and a female; however, there are more eccentric methods as well. For instance, parthenogenesis means that a female essentially clones herself. This already sounds strange, but it can get even weirder.

For example, the Japanese stick insect Ramulus mikado reproduces through parthenogenesis, yet males also exist in this species. A study published in 2025 in the journal Ecology aims to take a closer look at these insects and understand what is really happening with them.

Researchers are aware that the female of this species lays eggs that produce genetically nearly identical offspring. However, in some cases, males are born instead of females. Although this species is the most common stick insect in Japan, scientists have found only about a dozen males during their observations (which is almost like encountering a unicorn).

The advantage of parthenogenesis is evident in the short term—there's no need to search for partners, and a species can quickly increase its population. However, in the long term, this leads to the accumulation of harmful mutations and can even result in extinction due to an inability to adapt flexibly to new conditions. Therefore, the rare genetic anomalies that lead to the emergence of males could serve as an evolutionary "safety valve" that allows for gene exchange.

However, in the case of Ramulus mikado, it seems there are no chances for that. After finding a single live male, scientists introduced him to females and observed that he displayed typical courtship behavior and even attempted to mate. However, no DNA from the male was found in the offspring.

Upon conducting a detailed examination of six deceased males, researchers noted that some possessed a fully developed reproductive system, but no mature sperm was produced. In another specimen, signs of ovaries with eggs were discovered, which could indicate hermaphroditism.

The study of females also revealed that they have a fully developed but atrophied reproductive system. Thus, even in the case of successful mating, there would be no offspring at all.

Since there are no closely related species of R. mikado in Japan, and with a lack of fresh gene influx and the inability to reproduce with members of their own species, females are now left to bear the responsibility for the species' survival in their fragile hands. Moreover, it appears that the species has already lost too many genes, making a return to sexual reproduction highly unlikely. Therefore, it can be said that the species is in an evolutionary dead end from which there is no way back.

Regarding the males, scientists lean towards the idea that they appear due to some sort of "glitch" or random mutations. However, the possibility that this is an evolutionary remnant that will eventually disappear on its own has not been ruled out.

Interestingly, the species has managed to survive for hundreds of thousands of years, even in such a state. It seems that "life finds a way" despite all the challenges.

As previously reported, parthenogenesis has been observed in hammerhead sharks. At least one female was able to produce offspring while being completely alone in an aquarium.