I think they are just collecting wood-pieces which they chew and mix with salivary-gland-secretions and then use this micture to close their nests in wholes or such. If its social wasps they use it to make the "paper" 4 their nests. Well, i think they dont eat it anymore, if you use some impregnation 4 wood like special oils or such things (u ca buy that stuff usually in hardware stores and those kinds of shops). That should help. I dont know if theres any "natural" solutions for that, maybe try google 4 that.