Boom in raising monarch butterflies in Thunder Bay leads to rising demand for milkweed

An expert on monarch butterflies in northwestern Ontario says a shortage of milkweed in Thunder Bay is becoming a regular occurrence due to the popularity of raising the caterpillars.

Dan Fulton said many people are just getting into raising monarchs and don't realize one milkweed plant won't last long. He said even a large, adult milkweed will be stripped quickly by just a few caterpillars.

Fulton said the small milkweed plants often sold at greenhouses don't have the size to provide much caterpillar nourishment.

"We have so many new people getting involved with the monarchs and raising the caterpillars," said Fulton. "And unfortunately, they just don't realize how much these little guys can eat. They're ferocious eaters and for 12 days they're just building up their nutrition in bulk."

Fulton said part of the issue is that the survival of outside caterpillars is low, just three per cent. Yet when people bring them indoors the survival rate jumps to 90 percent and they run out of milkweed. Fulton also said that this year the monarchs came two weeks earlier than normal, so the milkweed plants and leaves were very small. He said the lack of mature plants for sale created some alarm.

"Common milkweed has a huge taproot, so you can't buy a three-year-old common milkweed plant," he said. "You can only get the smaller plants that are one year old. Common milkweed is preferred because there's huge leaves bigger than your hand. The other plants you can get are the swamp milkweed locally, which have a small, narrow leaf."

According to the Monarch Joint Venture (MJV) organization, female monarch butterflies typically lay 300 to 500 eggs on different species of milkweed plants but they've been known to lay more than 1,100 eggs in captivity. However, many of the eggs are eaten by spiders and stink bugs. The MJV said from the egg emerges a small, striped caterpillar or larva. As the monarch caterpillars grow, they become too big and replace the outer layer five times. The period between each molt is called an instar. At the end of the larva stage, the caterpillar finds a place to hang from so it can transition into a butterfly. Once attached, the caterpillar sheds its skin to reveal a jade-green chrysalis. After eight to 15 days, the monarch butterfly emerges.

 Fulton said the best strategy for people what want to raise monarchs is to plant a large number of milkweed this year, so they will be of a larger size next year. He said a three-year-old plant has the larger leaves that provide the most food.

Fulton said he has offered 12,000 milkweed plants up for sale over the last three years, with a portion of the money going to maintenance of the Adelaide Monarch Garden in Thunder Bay, which is privately funded and staffed by volunteers. He said the more milkweed people who raise monarchs can get into the ground, the better.

"I always say there's no no such thing as enough milkweed," he said. "But you really have to plan. Like if you've got X amount of plants, only bring in so many caterpillars. I know everybody wants to save every last one of them, but it just isn't feasible until you have enough plants."

Fulton said he expects there will be at least two more generations of caterpillars this summer before the last monarch butterflies leave the northwest, bound for Mexico.