Explain why before cold weather hydra reproduces sexually.

In many primitive animals, sexual reproduction occurs in stressful situations. This is due to the fact that during such reproduction, the offspring will carry the characteristics of both parents at once, which will increase the chances of preserving the gene pool. In addition, there is a chance that combinative variability will result in individuals that are more resilient, which, again, will increase the chances of passing these genes to future generations.

Cold is stressful for hydra. Eggs laid after breeding will hatch into larvae when conditions are favorable.