Missing Monarchs

Nature Notes for July 26, 2013

Monarch butterflies have been much in the news recently because of their scarcity. They had a hard winter in their wintering grounds in the mountains of Mexico. Very few have been seen in Ontario this year. Despite a large stand of common milkweed, their larval food plant, I have seen only one so far in my garden. In total I have seen only five or six Monarchs this year.

 Fritillary and Monarch on Swamp Milkweed

© Rod Lee

The butterfly stage is the adult stage of this insect. Many butterflies lay their eggs on a specific food plant. These eggs hatch into larvae (or caterpillars) which must feed, shed their skins several times to grow and then pupate. Although gardeners sometimes object to the larvae feeding on plants, without them, we would not have butterflies.

Like the Monarch, several other butterfly species migrate regularly into our area. In the spring of 2012, I wrote about a huge flight of Red Admiral butterflies, which was noticed by people who do not usually pay attention to natural phenomena. So far this year, I have seen only one Red Admiral.

The weather conditions in the spring of 2012 were hot and dry with lots of south winds. These conditions helped the migrant butterflies. Spring 2013 was cold and wet, and not conducive to butterfly migration. The species which migrate regularly into Ontario cannot tolerate cold winter temperatures so they must recolonize the province every summer.

Other butterfly species winter over in the larval or pupa stage and emerge with spring warmth. The Mourning Cloak, on the other hand, overwinters as an adult so can be found flying quite early in the season.

Each butterfly species has a particular flight season. At this latitude some have two flights per season, some only one. Further south they may have more flight seasons.

Although many adult butterflies live only a few weeks, some like the Monarch and the Mourning Cloak are quite long-lived. Mourning Cloaks that emerge in September can overwinter as adults and may have a life-span of almost 10 months. Compton Tortoiseshell adults emerge in July, overwinter as adults, and fly again from April to June. Some of these butterflies can become very faded and tattered, but can still fly and reproduce.

Most school children are taught that the Monarch larval food plant in only milkweed. Many other species are just as fussy. The Baltimore Checkerspot feeds only on turtlehead. Columbine Duskywing feeds only on columbine plants. The Karner Blue butterfly feeds only on wild blue lupines (but not on the cultivars grown in gardens) and has been extirpated in Ontario due to the scarcity of their food plant. Because of these species specific food requirements, they occur in local colonies. These colonies can easily be destroyed if the area is disturbed. Other species feed on a wider variety of plants so are less vulnerable to disturbance.

Migratory butterflies are strong fliers, but many butterflies do not fly strongly. These species do not disperse very far from their larval food plants.

Last Sunday (July 21), a butterfly focused outing of Willow Beach Field Naturalists turned up 22 species of butterflies along a local roadside. This area offered a variety of habitats – wet, dry, wooded, open field. The most exciting find was the number of Baltimore Checkerspots – several nectaring on each bloom of swamp milkweed or Joe Pye Weed. 

Baltimore Checkerspot on Swamp Milkweed

© Rod Lee

We only saw one Monarch. It will be interesting to see what the fall migration of Monarchs brings.