The elm sawfly larvae can be found in a variety of colours from this lemon yellow, to a pale yellow, salmon pink, light green, and shades in between. They get much bigger than this little one. As adults they look like large wasps but they are not, nor can they sting: https://pbase.com/laroseforest/image/106079624 Sawflies belong to the same order as bees and wasps and are in essence a sort of primitive wasp with no ability to sting.