For the past couple of summers, Environment Canada biologist Syd Cannings has led expeditions into the wilds of the Yukon’s sand dunes in search of a rare beast – a fly.
A fly? Surely we have plenty of flies. But this, Cannings explains, is the dune tachinid fly, a speedy little creature that has been found so far in only a few widely-separated places around the world. It’s about as big as a medium-sized house fly and looks black when you glimpse it zipping by. Up close – preferably magnified – it has translucent wings and pale grey patterns on its body.
The dune tachinid fly is so rare that Monty Wood, the Agriculture Canada scientist who first spotted the fly in the Carcross Desert in the 1980s, thought it might be a new species found only in the Yukon. He
searched sand dunes in Alaska and northern Canada without turning up another specimen.
Later, the fly he collected from the Carcross dunes was compared with specimens in Europe and identified as Germaria angustata, found previously at a few coastal dune sites in Europe and inland in central
Asia. It was collected only once in 60 years in England and once in Siberia, although there are more sightings from Mongolia.
The Yukon, however, is a relative treasure-trove of dune tachinid flies. “If you go out in late June or early July, you can find a bunch of them,” says Cannings.
And they’re not just in the Carcross Desert. Cannings and his team found the flies in sand dunes along the Takhini River, in a large area of dunes at the junction of the Kaskawulsh and Alsek rivers, at the north
end of Sekulmun Lake, and even in patches of wind-blown sand at the top of Whitehorse’s clay cliffs.
They were particularly numerous at the Alsek site, he says. “We could catch 40 in a couple of hours.”
Dune tachinid flies may be more plentiful than anyone thought, but we still don’t know much about them. However, we can make some good guesses, based on other tachinid flies.
Tachinid flies always parasitize other insects, Cannings says. They lay their eggs where the newly hatched larva will find the right kind of caterpillar, usually a moth caterpillar, and the fly larva burrows in. It
lives inside its host, feeding off it as the caterpillar goes about its business. When the fly larva finishes growing, it digs its way out of the caterpillar.
“It’s like the movie Alien,” says Cannings. “You’ve got this one thing living inside you, and when it emerges, it kills you.”
Both Cannings and Wood suspect that the fully grown fly larva transforms into a pupa (the next stage in its development) beneath the sand’s surface and overwinters in that form.
“Then it emerges in mid-June, finds a mate and lays its eggs on the grass, the larva hatches to attack the already large-ish moth caterpillar, and then pupates,” says Cannings.
That’s its probable life cycle, but nobody really knows for sure. Because the fly is so rare in Europe – and had never been found in North America until it turned up in the Yukon – very little research has been
done on it.
Monty Wood suspects the larvae might parasitize the cutworm caterpillars of a moth called the Coast Dart. They burrow into the sand by day and come out at night to eat grass. The moths have been found in
the same places where the flies are found, but the link between the two has not yet been established.
The relative abundance of dune tachinid flies in the Yukon means that could change, says Cannings.
“We’re in the position of answering a lot of these questions, if we just got out there and spent time with a shovel!”
In fact, we may be in a position to answer even more questions. After two summers of field work, Cannings and his crew have found the dune tachinid fly at 12 sites in eight different areas. They’ve also found a
couple of dozen other species of tachinid fly, some of them possibly new to science, and several species of moths and other insects.
Some of these tiny creatures may be survivors from the days of Beringia, when ice age giants roamed open grasslands in the Yukon, Alaska, and Siberia, cut off by the glaciers from the rest of North America.
“The lions and mammoths may be gone,” says Cannings, “but many of the plants and smaller animals special to Beringia are still here, creating unique communities.”
For more information about the ecology of the Carcross Desert, see Your Yukon column #191 at www.taiga.net/yourYukon/col191.html.
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.