Ingestion and assimilation rates in six species of tropical millipede (Diplopoda: Spirostreptidae) from southern Africa are estimated for the first time and were found to vary both within and between species. A proportion of this variability was attributable to variation in body size effects as individuals ranged from 0.2 to 2.9 g dry mass. Mean ingestion rates for each species were 17,30, 34.32 and 75 mg dry leaf litter per day (7.6 to 2.6% of body mass). Within species, ingestion rates explained between 35 and 53% of the variation in assimilation. Large size did not necessarily enhance assimilation efficiencies, which were between 7 and 26%) and comparable to assimilation efficiencies reported for temperate species, but did result in greater absolute ingestion and assimilation of organic material per individual.