A Danger?

David Hall

Dendrobatid frogs have been a passion of mine for over 15 years and the obsession of keeping these animals has opened my eyes to other delights such as orchids, ferns, small creepers (vines) exotic carnivorous plants and mosses.

I have managed to get hold of a tropical moss, often offered on websites on the 'net that will grow slowly on cocoa panels or tree-fern slabs if kept moist.  It can handle temperatures up to 26°C. I use native mosses for the floor of the vivaria and this provides live-food in the form of springtails, small flies, worms, moths and beetles, but also problems in the form of slugs, big spiders and in particular, a flatworm... (here the author mentions New Zealand in relation to the flatworm, either intentionally or unintentionally - see notes and pictures below).

These are not the huge monsters that suck the life out of our native earthworms but a small, 10-20mm species, beige and chocolate brown in colour, around 2-3mm in diameter.  It moves in a snake-like fashion and reproduces within itself. Its head narrows to a shear point and it feels its way along until it comes across its prey.

I have seen these worms in my vivaria for some years now and the frogs do not seem to eat them. However, I became concerned when I saw one devour a cricket 2-3mm long.  Since then I have been removing them from the vivarium whenever I can.

The question is....  Do the worms pose any threat to the frogs?

Editor's Notes:
I did a quick search on the internet, and came up with the following notes on the (now) well documented pest of earthworms.  You may like to visit

http://www.csl.gov.uk/resdev/environ/alien/flatworm/project/index.htm

New Zealand Flatworm
Arthurdendyus triangulatus (formerly Artioposthia triangulata)
The New Zealand flatworm is not native to the United Kingdom. It was first recorded in Belfast (1963) and shortly afterwards in Edinburgh (1965).  Although apparently widespread over Northern Ireland, it seems to prefer the cooler, wetter climate of the west of Scotland. On the drier, eastern side there have been fewer sightings. In its native New Zealand, the flatworm is found in shady, wooded areas and only on the cooler South Island. Open, sunny pasture land is too hot and dry; temperatures over 20°C are lethal to this creature.It has also been identified at isolated points throughout the UK. A major survey in spring 1995, has shown that this pest has a much wider spread than was assumed.

Description
The photograph left shows a flatworm in its native habitat in New Zealand, near the sea at Ngawi, the southern-most tip of North Island (picture by John Skillcorn).  Here it was very common underneath rocks and rotting wood.  

When resting, worms will be coiled and covered in mucus. They are very distinctive and look nothing like earth worms. The upper surface is dark, purplish brown with a narrow, pale buff edge. The underside is also pale buff. They are pointed at both ends, and ribbon-flat. A mature flatworm at rest is about 1cm wide and 6cm long. When extended, it can be up to 30cm long, and proportionally narrower. Flatworm `eggs' or capsules (right) are shiny black, just under 1 cm long, and like a misshapen blackcurrant. They contain as few as two, or as many as eleven young worms.

How it spreads
Flatworms were probably introduced into the UK via the soil in pot plants sent or brought from New Zealand. They favour dark, damp conditions such as would be found between potting medium and pot, and under the rim of plant trays. Newly bought plants should have the potting medium, and the root ball thoroughly searched before planting.

Feeding requirements
This flatworm seems to eat earthworms exclusively. There is no evidence that it will eat any other soil-dwelling creatures, even when the earthworm population has been reduced to below detectable levels. It has no apparent preference for one particular species, although it is most active near the soil surface. Deeper burrowing earthworms are consequently more likely to survive despite the presence of flatworms.

When an earthworm is located, the flatworm covers it with digestive juices. This dissolves the earthworm which is then sucked up by the predator. Estimates suggest that flatworms consume one or two earthworms per week. When its food supply has been virtually exhausted, a flatworm will shrink and wait until there are sufficient earthworms for feeding to restart. This waiting time can be as long as 12-24 months. It is not yet clear whether flatworms will move long distances to alternative feeding sites.

No need to panic
The presence of New Zealand flatworm in well-maintained gardens does not seem to be quite such a disaster as was first thought. In Northern Ireland, one organic smallholder has co-existed with this creature for about 12 years. He has managed to trap and destroy large numbers of flatworm. This has enabled his earthworm population to re-establish itself. Regular additions of large quantities of organic material have created such a healthy soil that a temporary reduction in earthworm population has been tolerable.

There are several botanic gardens in which flatworms have been found. The staff employ identical methods of control and care as the smallholder, and their gardens show no sign of any problems associated with lack of earthworm activity.

The situation is less straightforward for farmers managing pasture land. Fields which are unploughed have become waterlogged without the regular burrowing activity of earthworms to aerate the soil.

Check your garden
The New Zealand flatworm prefers undisturbed resting sites. Look underneath large plant pots, garden ornaments and big stones. If you find one flatworm, there are probably more. Eggs are usually found between June and September. A trap can be set by weighing down a plastic sack in a damp area of the garden. Inspect the underside regularly for coiled flatworms.

What to do now you have found a New Zealand flatworm
Please place the specimen (alive if possible) in a solid container, such as a photographic film container, with some wet moss or kitchen roll and send to one of the following people.

Scotland
Dr Brian Boag
Scottish Crop Research Institute
Invergowrie
Dundee
Telephone: 01382 562731
bboag@scri.sari.ac.uk

Northern Ireland
Mr J.P.Moore
DARDNI
Newforge Lane
Belfast
BT9 5PX
Telephone: 01232 255288
paul.j.moore@dardni.gov.uk

England and Wales
Dr Mike Lole
Plant Clinic
ADAS
Woodthorne
Wergs Road
Wolverhampton
WV6 8TQ
Tel: 01902 693305
Fax: 01902 693304
Mike_Lole@adas.co.uk

Controls
Birds have eaten flatworms, with no ill effects, but the natural habitat of the pest is usually under cover, concealed from searching beaks. Recent research has revealed that the larvae of native ground and rove beetles prey on adult flat worms. Beetles, larvae and flatworms all inhabit the same environment. No chemical controls exist which will not also harm earthworms. If found, flatworms should be destroyed by squashing burning or immersing in salty water.