Maritime ringlet butterflies (Coenonympha tullia nipisiquit McDunnough) are rare, endangered salt marsh butterflies with larvae that survive periodic tidal submergence. Only six disjunct populations are known to exist. First-instar larvae were released and monitored in seven microhabitats within a salt marsh in Bathurst, New Brunswick, Canada. From resighting data, microhabitat-specific daily death rates were estimated with maximum likelihood. The survival of the larvae released in groups was compared by calculating minimum number of larvae known to be alive (MNKA). Death rates were low in microhabitats with the larval host plant, salt meadow cordgrass (Spartina patens (Aiton) Muhl.) and the major nectar source, sea lavender (Limonium carolinianum (Walter) Britton), a habitat with a moderate frequency of flooding. Because microhabitats have a large effect on the survival rate of young larvae, use of microhabitat profiles in salt marshes as habitat-quality indices is recommended in critical-habitat assessment and reintroduction efforts.