The hardy travellers can fly for 3,000 miles from the north-east US and Canada to roost in their millions in Mexico
Imagine your body was the weight of a raisin, supported by just a pair of flimsy, gossamer wings. Now imagine that you had to fly for 3,000 miles, avoiding storms, highways and predators, to ensure your species continued.
Could you do it? Unless you’re a monarch butterfly, fortunately you won’t have to face such a challenge.
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