This name refer to the preference of these insects for moist areas and to the fact that they carry three stripes on the breast shield.

For terms see Morphology of Diptera Helophilus trivittatus has a wing length of 10.25–12.25 millimetres (0.404–0.482 in).

[12] These hoverflies inhabit wetland, river margins, seasonally flooded grassland and salt-marsh.

Adults feed on various flowers, including umbellifers, yellow composites, Armeria, Aster, Cakile, Centaurea, Chrysanthemum, Cirsium, Crataegus, Chamaenerion angustifolium, Eryngium, Eupatorium, Euphorbia, Ligustrum, Lychnis, Lythrum, Mentha, Menyanthes, Origanum, Plumbago, Polygonum persicaria, Potentilla, Ranunculus, Rubus fruticosus, Salix and Sorbus.

[14] The larva is a detritivore associated with decaying rhizomes of Typha latifolia and with beds of Glyceria maxima.