Legless in the Yukon

Over the last few years, while conducting field work in the northern Yukon, Bruce Bennett has turned up some unexpected bits of wildlife -- a few small worms wriggling through the damp, shallow soil of the tundra.

By Claire Eamer

Over the last few years, while conducting field work in the northern Yukon, Bruce Bennett has turned up some unexpected bits of wildlife—a few small worms wriggling through the damp, shallow soil of the tundra.

Bennett, a Yukon government biologist, was surprised to find “earthworms” so far north.

However, worm expert Valin Marshal of Victoria says at least one of the tiny worms isn’t an earthworm at all. It belongs to a related group, the enchytraeids, which are also called iceworms or potworms.

Another of Bennett’s finds, from the Peel River valley, is indeed an earthworm, or lumbricid. Ontario expert John Reynolds recently confirmed the identification based on Bennett’s photograph of the little animal.

The photo wasn’t enough to determine the worm’s species, but it’s still an extremely rare find. Most worms found in the Arctic are potworms, not earthworms, Marshal says.

It’s not easy to tell the difference between earthworms and potworms. Potworms are generally smaller than earthworms, but some large potworms could easily be mistaken for earthworms, says Marshal. Potworms like wet habitats, but so do some earthworms.

The most obvious external difference is that earthworms have pigment that gives their bodies some kind of colouring. Enchytraeids are translucent. The other differences are generally too small to see without magnification, or they’re internal.

“There are not too many people in Canada who can tell these things apart,” says Marshal.

Both lumbricids and enchytraeids live in the Yukon, but we have only a broad idea of which worms are present, where they live, and where they came from.

We do know that a lot of the earthworms are fairly recent immigrants. A limited worm survey by Syracuse University graduate student Chelsea Teale a couple of years ago turned up four earthworm species in gardens and parks in Whitehorse. Two of them arrived in composting material discarded by Whitehorse in 2004.

Others have been introduced by residents doing their own composting or trying to improve their garden soil. Sometimes worms arrive along with soil or plants imported from other locations.

“At least seven earthworm species are known from the Yukon,” says Marshal. “Most of these earthworms were likely spread through human activity during the last century.”

However, a couple of species could have survived in the Arctic right through the last glacial period. Both Bimastos parvus and Eisenia nordenskioldi have been found in Russia, in terrain and climate much like the Yukon’s. The little worm from the Peel River might be one of these two species.

Bimastos parvus has been spotted in the Yukon before, on the east shore of Kluane Lake and in the Sheep Mountain area. Marshal says Eisenia nordenskioldi could be in the Yukon too. It’s widespread in northeastern Siberia and Wrangel Island, just across the Bering Strait from Alaska and the Yukon.

“Many of these earthworm species are very widely distributed, if you look in the right place.”

Potworms, on the other hand, are fairly common in arctic regions. They like wet conditions, Marshal says, so you find them on seashores, in sewage sludge, and even in habitat that is more water than land.

They are more tolerant of cold than earthworms, and they have a reproduction strategy that suits northern conditions. Both earthworms and potworms deposit both sperm and eggs in cocoons. Baby worms develop and grow in the cocoons.

However, the cocoons can stay dormant for a long time, even through an arctic winter, until conditions are suitable for young worms to hatch out. Enchytraeids increase their reproduction odds even more by producing lots of cocoons in a season.

“These animals are pretty resourceful,” says Marshal.

We have a lot to learn about worms, but few people are studying them in Canada. Marshal, one of a handful of experts in Western Canada, retired recently, and he says not many people are entering the field.

“It’s not a very well-paying profession currently.”

Worm experts are needed if we’re to understand ecological processes and how they are changing, but it’s hard to attract students and funding.

And it’s hard to find the worms, especially in places like the Yukon, where pockets of worm habitat are scattered across a huge area.

“You need experts to scour the place and know where to look and how to identify them. Then you have to collect the worms properly in order to work with them.”

Both the taxonomy and ecology of worms are wide open fields for future biology students, he says.

For more information about earthworms in Canada, go to the website of the Worm Watch Program at www.frogwatch.ca/english/wormwatch.

This column is co-ordinated by the Northern Research Institute at Yukon College with financial support from Environment Yukon and Yukon College. The articles are archived

at www.taiga.net/yourYukon.