After any rain received, the Earthworms will be sending their annoying little soil casts up onto the surface of your lawns as the root zone gets a little soggy for them to move about in.
The more rain we get = the more worm casts as the soil water to air ratio reduces to favour the rain. Earthworms need to breathe and thus clean their burrows.
CastClear is the solution to lawn worm casts as the worms do not like the taste of this barrier product when applied to the lawn and are encouraged to stay deeper in the soil profile and not cast on the surface. Repeat after 20 days at 1/3rd the initial dose rate. The worms are unharmed by this nutrient based product.
You can get some online from The Lawn Shop