Tomato eating bug

[Nobby]

Hello all. I have three tomato plants in my greenhouse, one has grown in a 12 inch pot which is placed on a bench well above the ground area. The other two are in grow bags on the soil at floor level. The fruits have been doing very well. Unfortunately some of the produce has been attacked by what I can only describe as tiny woodlice, they are approximately 2 mm in length and have a very light grey covering, only the ripening ones seem to be affected, they have made channels approximately an 1/8" deep. The one on the bench seems to be un-affected. My question is; could they be woodlice? If so, is there any way I can eradicate the problem.

This is my first year of gardening and not really acquainted with the bugs I may have to contend with in the future.
Hope you can help. Many thanks. Nobby