Breeding occurs from March to May. The eggs are deposited in a cocoon. In the Delta area the pelagic larvae are found in February-June and August-October. Before spawning it sometimes swims close to the water surface.  

 In the western Wadden Sea E. longa appears to be relatively tolerant to low winter temperatures. The species crawls on the surface or in the upper centimetres of the sediment. Many phyllodocids are predatory carnivores, catching their prey with their muscular pharynx. E. longa feeds on spionids, e.g. Spio filicornis and Scolelepis squamata, and on a variety of small metazoans. Cannibalism is widespread (Hartmann-Schröder, 1971; Wolff, 1973; Beukema, 1979; Fauchald & Jumars, 1979).