Most markedly, Helophilus trivittatus has black and yellow stripes on its thorax that run front-to-back, similar to Helophilus pendulus.
This hoverfly is larger and longer than other hoverflies, so usually stands out even to a casual observer. Its abdominal side patches are lemon yellow in appearance. The central stripe on its face is also lemon yellow. Its hind tibia is two-thirds dark, rather than the more typical one-third dark that ones sees with other hoverflies.
This is another of our important pollinators.