By CPCA Environment Committee

This report describes the arrival of a new species to the biodiversity gardens along Pontiac Street in Champlain Park. A few years ago, a block of Pontiac Street was closed and de-paved to create a continuous green space between the City Park and the Ottawa River Pathway. As some residents will remember, the area was in deplorable state with broken fences, invasive buckthorn trees and abandoned gravel parking spaces. Volunteers with the Champlain Park Community Association environment committee cleaned up the site, dug out the gravel, and brought in soil for garden beds which were planted almost exclusively with over 100 species of native trees, shrubs and herbs including several considered “at risk”. Several gardens were created: a Mini forest of native trees, a pollinator garden, a Carolinian (warm climate) forest, native herb garden and ethnobotanical garden.

The new species that arrived for the first time this year (June 2025) is the giant swallowtail butterfly (Fig 1). These very large (14- 19 cm wingspan) butterflies with yellow and black markings have not been seen in the biodiversity gardens in Champlain Park previously. Why are they here now? They were attracted to their host plant and preferred food, the hop tree.

We planted hop trees (Fig 2) in one area of the biodiversity gardens along with other Carolinian trees from southern Ontario, in order to have plants adapted for warming in Ottawa predicted by climate models. Hop tree is a member of the Citrus family of trees and shrubs and has a lemony smell that attracts the butterfly. In southern Ontario, it grows along the shore of Lake Erie. The hop tree is a listed in Ontario as a species at risk which is “of special concern” because of habitat loss. Two small trees were planted here three years ago and are now thriving. An adult female butterfly was seen laying eggs on the hop trees by Catherine Shearer. Soon after, the eggs hatched to produce a very hungry caterpillar which grew quickly. The caterpillar has a digestive enzyme that detoxifies an insect feeding deterrent (furanocoumarins) produced in the leaves, giving this caterpillar access to food that it doesn’t have to share with any other insects. The caterpillars become large and are potentially food for birds but protect themselves by their great camouflage which makes them look like bird or animal droppings (Fig 3).

You may see the giant swallowtail butterflies feeding and pollinating flowers anywhere in the gardens this summer, although the larvae are now gone. However, other interesting insects and birds are also there (Figure 4).

We planted three species of milkweed, and sure enough their specialist insect, the monarch arrived. The adults feed on nectar from many plants in the pollinator garden and lay their eggs exclusively on the milkweeds. Red admiral, tiger swallowtail, cabbage butterfly and many smaller butterflies and moths are now common. You may also see their caterpillars like the colourful banded black swallowtail larva. The many flowering plants attract a wide variety of other insect pollinators including native bumble bees, solitary bees, sweat bees, wasps etc. Notable among them is the great black wasp which is also a recent arrival to this area in the last few years. Hummingbirds are attracted to tubular flowers in the garden, and we have seen ruby throated hummingbird visiting foxglove penstemon, red cardinal flower, obedient plants and blue lobelia.

You can visit the biodiversity gardens at the north end of Champlain Park along the unpaved section of Pontiac. More information is available by consulting the QR codes on posts at each site.