Caution! Butterfly!

Taiwan has shut a highway lane to traffic, lowered the speed limit and put up protective nets to help a butterfly species cross the road during an annual migration.

From mid-March and for about a month, thousands of Purple Crow butterflies fly over a section of freeway in central Taiwan as they move northwards to breed after spending winter in the island's warmer south.

Before the Taiwan Area National Freeway Bureau took protective measures in 2007, many butterflies were hit on the highways or killed by wind from speeding vehicles.

"More than 10,000 butterflies will spread their wings to fly high, bravely crossing the highway, on a different kind of life-or-death journey," the bureau said in a statement, calling the migration "one of a kind".

The roadkill rate of butterflies has fallen to 0.3 percent last year from 3 percent before the highway department took action, the bureau said.

The conservation project has cost T$ 2.8 million ($83,000) over the past three years.

The protective measures include a driving speed limit at 60 km per hour (37 mph), a 3 km (2 mile) road blockage when butterfly numbers exceed 500 per minute, and a 4-metre (13-foot) high protective net guiding the insects to fly above traffic.

Trees have also been planted along the side of freeway to provide a longer-term, natural net.

 YUNLIN COUNTY, Taiwan, April 2 (Reuters Life!)