Zillions of mosquito wrigglers

Brief return to the SW Woods today to collect some drowned earthworms..mostly gone now. I will have to remember to collect them soon as I see them after the next flood. In the shallow pools I checked, there were dense clusters of hundreds of mosquito wrigglers. They look near ready for pupation and emergence. Interesting that they cluster together in a group the size of an orange. What is the benefit of grouping together - escape from predators? I saw no dragonflies or other predators and I am afraid these mosquitoes are just about on the home stretch of their development to become adults. Just a few adults around now.. too few to be a bother.