Monarch Butterflies Mating At Lower Reesor Pond In Toronto

What a sad summer it was here in Toronto, Ontario in 2014, because Monarch Butterflies (Danaus plexippus) were conspicuous by their absence. Bob and I had been monitoring sightings posted by nature lovers on Facebook, and websites such as The Insects and Arachnids of Ontario, The Weather Network, and Butterflies and Moths of North America. We were not the only people discouraged by the poor showing of these beautiful insects so far this year.

We were heartened, however, on a visit to Lower Reesor Pond in Northeast Toronto because, as Bob and I hiked along the pond, we saw no less than half a dozen of these iconic orange butterflies. We were not able to get close enough to most of them for a photograph, but they were all in different areas of the overgrown meadow near the pond, so we feel confident in stating that each one was a different individual from the other.

These Monarch Butterflies mating , were in a stationary position on a small tree which is what made it possible for me to get some snapshots.

Only moments before, one of these butterflies was perched on a young Chokecherry Tree, and as I approached, it took flight. I thought my chances were gone, but the next thing you know, another Monarch flew in from the opposite direction and the two paired up.

The fact that these Monarch butterflies were mating does not guarantee that they will produce eggs. Only about thirty percent of such attempts will result in copulation. Whenever Bob and I come across a patch of Milkweed, we check the leaves for evidence of Monarch Butterfly eggs and caterpillars or larvae.

Only once, earlier this summer, did we find one egg on one leaf of one milkweed plant. Similar reports from such places as Wye Marsh Wildlife Centre near Midland, Ontario, have come up with equally as poor results. On July 15, the Program Coordinator at the Centre was successful in finding only two Monarch caterpillars, a number way less than usual.

The vegetation around Lower Reesor Pond does include a fair amount of the necessary Milkweed plants upon which Monarch Butterflies lay their eggs, and a good variety of wildflowers spot the grassy knolls and fields nearby, but what was disturbing was the swath of Dog-Strangling Vine growing along the fringe of the wetland on the west side. The spread of this vine is rapid and aggressive. It trails along the ground or wraps itself around trees and other plants, and patches of these plants are so dense that they choke out native plants and young trees.

I used to think that there were three major reasons for the decreasing numbers of Monarch Butterflies: loss of milkweed plants due to use of herbicides by agricultural corporations; Genetically Modified Corn that is bred to produce a bacterial toxin to protect against corn pests, the pollen of which, when it coats nearby milkweed plants, leads to the deaths of the Monarch larvae;

and the illegal logging of the Oyamel trees in Mexico upon which the Butterflies winter.

I recently learned, however, that there is another troubling threat to Monarch Butterflies that is flourishing in our own neighborhoods, and that is the spread of the dreaded Dog-Strangling Vine. There are two species of these non-native plants, both of which are relatives of our native milkweeds. Therein lies the problem. Monarch Butterflies are confused by this vine and lay their eggs on it, but once the eggs hatch, the toxicity of the leaves poisons the caterpillars so they die before they are able to complete their life cycle.

Given the timing of our sighting of this pair of Monarch Butterflies, I would say they were members of the second generation descended from their ancestors that left Mexico in February or March. Their eggs will result in the third generation, from which the next set of eggs will produce the fourth and final generation of butterflies this season. Each of these first three generations lives for only 2-6 weeks from the egg, through the larval stage to the adult. The final generation is different, however, and will live for 6-8 months during which time the Butterflies will return to Mexico, wait out the winter and then begin the return trip to Ontario.

The final generation of this season’s Butterflies are born to fly. The declining hours of sunshine and cooler temperatures of late summer will signal to them that they must ready themselves for their long journey. They will depart Ontario in September or early October, before the cold weather threatens their survival, to undertake their incredible 3,000-mile (4,828-kilometre) flight back to Mexico. Let’s hope they make it home safely.

If you find dog-strangling vine or other invasive species in the wild in Ontario, you can contact the Invading Species Hot line at 1-800-563-7711 or by email at info@invadingspecies.com

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