for the first one i would say that he uses spear for nettle because if you touch the nettle it hurts and starts to itch very much which could be for example of spears (painful)
for the second one regiment of spite would be like group of nastiness means that the nettles are nasty or mean when they touch you ,that the boy might of thought that it was angry at him because if the story says so he was touched by them very much or stung him very much
