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Unlike many of the medusae, siphonophores feed while drifting motionless, creating a “curtain of death” with their extended tentacles. Prey must blunder into the “curtain” for siphonophores to feed. Most calycophorans and physonects spread their tentacles for short bouts of swimming (Figure 3.33) followed by longer periods of drift, usually several minutes in larger species. The frequency of swimming episodes for the purpose of tentacle‐reset scales roughly inversely with size, with the larger physonects swimming every few minutes and smaller calycophorans every minute or less. Species with large siphosomes, e.g. Apolemia at 20 m or greater, assume a horizontal position with the tentacles hanging down in a curtain. Swimming is less important for spreading the tentacles in the longer species (Mackie et al. 1987). Changes in the tentacle net happen gradually as structures sort themselves by density, sinking or rising with time. In some physonects, prey are tempted by periodic contractions of tentilla, mimicking the motion of zooplankters. In some cases, structures on the tentacle such as nematocyst batteries resemble “prey of the prey” and bring unwary prey species within the kill zone.