Why do hydras reproduce sexually just before the onset of cold weather?

Hydras can reproduce sexually and asexually. Asexual reproduction is typical for hydras only in the warm season, that is, in favorable conditions. Hydras switch to sexual reproduction at the onset of cold times. When cold weather sets in, hydras die, and their fertilized eggs sink to the bottom and easily tolerate cold and lack of light there. And with the onset of heat, the process of egg development starts, and new hydras appear, which are also capable of asexual and sexual reproduction.