Why do earthworms surface after a rain?
It looks like certain species of earthworms need to surface because they have higher oxygen consumption, while other species do not need to surface because of their lower consumption.

In particular, specimens of Amynthas gracilis were found to have low water tolerance, hence they


  crawl out of the waterlogged soil, especially at night when their oxygen consumption increases


while Pontoscolex corethrurus 


  survived longer under water and was never observed to crawl out of the
  soil after heavy rain




Role of diurnal rhythm of oxygen consumption in emergence from soil at night after heavy rain by earthworms