Feeding Behaviour and Prey Choice in Macroperipatus torquatus (Onychophora)

V. M. St J. Read, R. N. Hughes


Macroperipatus torquatus feeds nocturnally on crickets and a few other invertebrates on the floor of the Trinidadian rain forest. Prey are inspected by gentle application of the antennae and, if suitable, are captured by entangling them in proteinaceous glue squirted from the oral papillae. Entangled prey are bitten through an arthrodial membrane and immobilized by injected saliva, which may also partly digest the flesh. Ingestion of the flesh takes several hours, comprising some 90% of total handling time, and normally only one prey item is eaten per night. The deplected carcass is discarded. Fully charged glue reserves amount to about 11% of body mass and after exhaustion are replenished in about 24 days. The quantity of glue used in an attack increases up to about 80% of reserve capacity for larger prey. Glue adhering to the prey is ingested, but some attached to the substratum is always lost. Squirting glue may therefore be costly for two reasons. Firstly, depleted glue reserves render peripatus less capable of attacking further prey or of defending themselves; secondly, unrecovered glue together with the metabolic cost of glue secretion will detract from the energetic yield of the prey. Small prey will scarcely repay the cost of glue used whereas larger ones are more likely to escape; consequently the energetically optimal prey are relatively large, but somewhat smaller than those potentially available. Accordingly, adult peripatus preferred larger prey and grew better when fed on them in the laboratory, whereas juveniles grew better on smaller prey. The size distribution of prey in the forest was heavily biased towards smaller types and it seemed likely that the productivity of large peripatus would be limited by the availability of profitable prey.