We sat in a forest in the highlands of central Mexico, our gaze transfixed by strange dark clusters in the treetops. We were waiting for a miracle.

As independent travellers planning a rough itinerary we had read about the Monarch butterflies. For half a year they live in Canada, but in Michoacán state grows the milkweed, a plant on which they and their larva like to feed. Every October millions migrate here for the winter to reproduce before returning north in April. "500 million - they have counted them," said Hernán, our truck driver.

During these months they cluster together in the tall conifers until touched by the warmth of the morning sun. Then their wings unfold and all at once they descend to the ground, turning the whole world orange.

Hernán's truck chugged for 45 minutes just to cover six miles up a bone-shaking road that climbed from 2,800m to 3,100m, each bend revealing another breathtaking view. Groups of school children passed us on the way down - every day they walk the whole way to and from the village from outlying farms.

Hernán left us at the bottom of the steep path leading to the sanctuary, reminding us to walk slowly because of the altitude. The path wound upwards, deep into the woods. Dead and sleeping butterflies littered the trail, our obligatory guide frequently stooping to lift one gently to safety. Sadly, our meagre Spanish could not cope with his chatter; there were many questions we would have liked to ask. At last he stopped and pointed up into the tallest trees. The tops were almost obscured by clumps of what appeared to be a kind of parasite - massive, pendulous growths, clinging to the trunks and hung from every branch.

That figure of 500 million no longer seemed fanciful. We could hardly believe we were seeing nothing but butterflies.

So began our long vigil in that still, lonely forest. We lost track of time as we sat staring up into the trees, watching the clouds chase across the sky and willing the sun to break through. We tried to ask how soon the butterflies would fly, and gradually it dawned on us what the guide was trying to tell us: that if the cloud persisted all day they might not waken at all.

No-one had prepared us for this awful possibility. We’d come so far. How long could we stay? How long would Hernán wait? I could have wept with frustration and disappointment.

Then at last, just after noon, the miracle happened. The sun suddenly burst forth and slowly those dark brown clusters began to change colour to bronze... chestnut... orange... it was autumn speeded up. A gentle pattering sound like rain could be heard as thousands of tiny wings started to flutter and then to fly. They filled the glade and swirled through the trees, and they were all around us, a snowstorm of dancing orange butterflies.

Too soon we had to descend to the real world. But for a while the enchantment went with us. As the sun’s rays moved down the hillside they touched each tree in turn, and one by one they released their burden to join in the shimmering dance.

By now other people were straggling up the hill. We were glad we had come early, when the magic had been ours alone.

By Joan Bennett.

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