They will most certainly be Mason bees. The good news is that they are solitary bees and don't sting or swarm. As for your lawn you will just have lots holes in the area they are burrowing in but they are so small it will hopefully make no difference. Hope it helped.

If I remember correctly, there are rules of protection towards bees, which i think is espcially due to the rapid decline.

Everything should be fine. You never know they may be good lodgers and pay the rent on time. :o)

I have Mason bee boxes and renew them every year, when they are filling the tubes with their young the bee goes away to collect earth that is damp, to plug the hole, this might be what your bees are doing or they might be nesting, if so, they only lay their young in the hole and seal it up, then fly away. The young take a year to mature and will fly out next April and start the process over again. These bees are wonderful and they do not harm, let them be, they are the ones that pollinate our fruit and flowers. Our grandson stands and watches our boxes, he is facinated by them.