It's been a great spring for butterfly watchers in Hamilton.

Thanks to the warm weather butterflies have migrated across Eastern Canada in unprecedented numbers.

"It's probably the most exciting year for butterflies that Canada has ever seen," said Jeremy Kerr, a professor of biology at the University of Ottawa.

Kerr said estimates from the field suggest there are 300 million red admiral butterflies from Windsor to New Brunswick —  more than 10 times what would be seen in a typical year. Numerous other butterfly species have also arrived or appeared in greater numbers.

People in Hamilton should already be seeing more butterflies than usual.

"Anytime I turn around there are red admirals out there," said Victoria MacPhail, director of publicity and outreach with Pollination Guelph.

MacPhail said the red admiral butterflies are fairly common and "look like a Monarch but the patterns are quite different".


What are red admirals?

Red admiral butterflies, Vanessa atalanta, are found throughout North America.

Smaller than a monarch, their black, orange (some say red) and white wings are between about 4.5 and 5.7 centimetres wide. Red admirals are extremely adaptable and can sip nectar from almost any kind of flower.

They are often seen in gardens.

The explosion in butterfly populations is mostly due to the warm weather this winter throughout North America. It caused butterflies to emerge from their overwintering forms in places like Texas and Florida sooner, and then improved their survival rates as they headed north.

The first local butterflies (ones that winter in Canada) were seen as early as March — which Kerr said was "damned peculiar" — and southern Ontario was hit by its first big wave of migratory butterflies in mid-April, thanks in part to strong winds.

The red admirals moved so far north so early that they flew into areas with snow, something that normally wouldn't happen. They were also joined by the painted lady, a closely related butterfly.

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A second wave arrived in early May, boosting the diversity in southern Ontario, especially from Windsor to Toronto. Kerr said one enthusiast recorded 22 different species in a single Windsor park.

Macphail says the five species people in Hamilton are most likely to see are red admirals, American painted ladies, question marks, morning cloaks and azures.

Looking for a good spot in Hamilton to butterfly watch? Sabrina Hall, manager of customer programs for the Royal Botanical Garden's suggests Cootes Paradise, the lilac dell in the arboretum at the Royal Botanical Gardens and "any meadow with lots of flowers on a sunny day."