Fróðskaparrit - 01.01.1992, Side 48

52
THE EXOTIC LAND PLANARIAN .. .
Figure legend
Figure 1. Faroese potato fields as an ideal habitat for
earthworms and the predator land planarian A. triangu-
lata
The special reimavelta technique involves the follow-
ing sequence: (a) the intact grass sward in the infield;
(b) the grass sward is cut into altemate narrow and wide
strips of turf; (c) seed potatoes plus a little fertiliser are
placed on top of the narrow strip of turf; d) the wide
strip of turf is cut free and folded over the adjacent nar-
row strip, so covering the potatoes during the growing
season; (e) after harvest, the turves are returned to their
former position so re-establishing the grass sward.
(After Joensen, 1980). Stages (d) and (e) promote
favourable habitat conditions for high density popula-
tions of earthworms and subsequently A. triangulata.
beneath the turves (>50 individuals per turf
on average), including several species such
as Dendrodrilus rubidus, Dendrobaena
octaedra, Lumbricus rubellus and
Aporrectodea caliginosa. Also obvious
were the entrance holes of numerous earth-
worm burrows. There was no sign of the
land planarian.
The pattem emerging for those potato
fields examined was clear and consistent:
when land planarians were present, earth-
worms were absent, and visa versa.
4) The arboretum in Tórshavn
The arboretum in Tórshavn obtained its
present site in 1977, the conservator’s gar-
den nearby being used prior to this for the
cultivation of plant material originating
from various countries in both the northem
and southem hemispheres (T.G. Leivsson,
pers.comm.). There had been no previous
reports of the land planarian at the arbore-
tum.
A search of the area in November 1992,
however, revealed several egg capsules in
the north-eastem comer of the arboretum,
though there was no sign of the planarian in
the nursery area. The egg capsules were
found under stones which were the remains
of a stone wall surrounding an old, well-
established garden with non-native plants.
Earthworms and other soil invertebrates
were also observed in the arboretum.
Laboratory observations
During sampling, it was noted that many
inactive individuals of A. triangulata
became active when disturbed. In the labo-
ratory, the land planarians were observed to
move rapidly when held in large plastic
containers; crawling activity incorporated a
characteristic lifting with a sideways move-
ment of the anterior end.
Examination of random samples of egg
capsules revealed different stages of devel-
opment per sampling site, egg capsule con-
tents ranging from a milky fluid to devel-
oped juveniles. It was also observed that
several egg capsules hatched within 24
hours at room temperature. Dissection of a
random selection of egg capsules (repre-