On the status of Arcitalitrus dorrieni (Crustacea: Amphipoda) on the island of Colonsay,Inner Hebrides

The presence of the landhopper Arcitalitrus dorrieni (Hunt) is reported on the island of Colonsay, Inner Hebrides. It is widely distributed there amongst deciduous leaf litter in forested areas but also occurs in bracken litter and scrub grassland. The species is an introduction from Australia, doubtless transported inadvertently among plants brought to the gardens at Colonsay House. It is, however, not restricted to the ornamental plantings but has colonized native woodland. Maximum population density recorded under leaf litter was 680 m². Amphipods avoid waterlogged or dry situations preferring to burrow in moist soil under litter from deciduous trees. Coniferous woodlands are more sparsely colonized. Rate of spread (minimum) from the original locus is calculated at c. 25 m/year. Arcitalitrus may prefer to eat sycamore leaves (cf. oak, beech). Ovigerous females are reported for May but no evidence exists for a release of young any earlier in the year. Immature amphipods seem to live more covert lives in the soil beneath the superficial litter layer. Eggs are relatively large and few in number. Amphipods may avoid ants but may have a mite living in phoretic or ectoparasitic association.