Feeding Ecology

Hermit crab mouthparts, from top to bottom: mandible, maxillule, maxilla, maxilliped 1, maxilliped 2 and maxilliped 3. Ilustration: Storm Martin 2012, adapted with modification from Kunze and Anderson 1979

Hermit crabs are generally considered to be omnivorous detritivores (Ingle and Christiansen 2004). They may filter feed, scavenge and are also opportunistic predators (Lancaster 1988). For hermit crabs, taste is more important than vision when finding food. Chemoreceptors (taste and smell receptors) are predominantly based in the aesthetascs of the antennules but are also present in the setae of the mouthparts, pereopods (walking legs) and the inner edge of the chelae (Lancaster 1988). A common mechanism of feeding observed in hermit crabs is direct scooping of sediment towards the mouth by either the maxillipeds or the smaller of the chelipeds (Ingle and Christiansen 2004). Sediment is then processed by the maxillipeds and maxillules before ingestion. The brushes of setae covering these appendages scrub the sediment, extracting detritus and discarding unwanted material. Similarly, when filter feeding, a current created by the beating of the maxillipeds, draws in particles which are trapped by setae (Brightwell 1951). Both techniques were observed of D. megistos at Heron Island. As well as scooping sediment, the chelae may be used to pick or scrape food, such as algae, from a surface (Lancaster 1988).

As predators, hermit crabs opportunistically exploit a range of other invertebrates; brittle-stars (ophiuroids), bivalves, amphipods, small shrimp, barnacles, polychaete worms and heart urchins have all been documented as being taken on occasion, by various species (Brightwell 1951, Lancaster 1988). Cannibalism is common for many species (Hazlett 1971) and hermit crabs have even been known to eat their own appendages when crushed, damaged or removed (Brightwell 1951). Larger species such as D. megistos will likewise feed on other smaller species; at Heron Island this potentially includes D. lagopodes and Calcinus gaimardii. Being large and attractively coloured, D. megistos is not uncommon from the aquarium trade, though it is considered a destructive species by many and has a reputation for opportunistically predating upon almost anything housed within the same tank of equal or smaller size. This reportedly includes a variety of invertebrates but also fishes, including toxic boxfish.

Heron Island is a nesting site for green turtles (Chelonia mydas) and hermit crabs have been reported to opportunistically prey on hatchlings from the Great Barrier Reef (Booth and Peters 1972). Such reports usually concern land hermit crabs (Coenobitidae) and littoral species, presumably species such as D. megistos rarely come into contact with turtle hatchlings.

The mouthparts of Dardanus lagopodes, a sympatric and morphologically very similar species to D. megistos. Photo: Storm Martin, Heron Island, 2012