BUTTERFLIES AND MOTHS
(Lepidoptera)
J.D. Lafontaine
RECENT CHANGES IN DISTRIBUTION
Recent changes in Lepidoptera distribution involve both expanding ranges and contracting ranges. Natural changes in distribution can be difficult to detect because they tend to be slower and more subtle than the dramatic changes caused by man. Unfortunately, most expanding ranges involve introduced species and most contracting ranges relate to the destruction of natural habitats.
Probably the most dramatic range changes involve introduced species. Two of these are butterflies: the European Skipper (Thymelicus lineola), introduced at London, Ontario about 1910 has become a major pest of Timothy Grass and is now abundant through much of eastern North America as far south as South Carolina and parts of the west; the Cabbage White (Pieris rapae), introduced at Quebec City about 1860 has spread throughout most of North America. More recently, the cutworm Noctua pronuba was introduced at Halifax, Nova Scotia about 1979. It reached Ontario in 1992 and has now spread west to Wisconsin and south to Maryland. Infestations of the Gypsy Moth (Lymantriidae: Lymantria dispar) in the Ecozone have had an impact on other Lepidoptera both through changes to the forest through defoliation and the effects on non-target Lepidoptera of the spraying program to control the caterpillars.
About ten of the approximately 40 introduced species in the Ecozone are household pests. These include cloths moths (e.g. Tineidae: Tinea pellionella and Tineola bisselliella), and meal moths (Pyralidae: Plodia interpunctella and Pyralis farinalis).
The introduction of foreign species continues. Five of the ten introduced cutworm species in the Ecozone have arrived in the area only in the past ten years.
Changes in distribution among native species is usually more difficult to document because it requires the use of negative evidence. For example, if a species has moved in to an area, or has withdrawn from an area, these can only be demonstrated if the lack of collections can be taken as valid evidence that the species is, or was, indeed absent. Five species of butterflies were believed to be extirpated from the Ecozone. Two of these, the Southern Hairstreak (Satyrium favonius) and Gorgone Checkerspot (Chlosyna gorgone), had not been seen in Ontario since 1919 and 1891 respectively (Campbell et al., 1990). In 1996 five colonies of Gorgone Checkerspot were discovered in Eastern Ontario and it is possible that the Southern Hairstreak still persists in the province. The Karner Blue (Lycaeides melissa), Frosted Elfin (Callophrys irus) and Persius Skipper (Erynnis persius) have disappeared from the Ecozone only in the past ten years, yet it is less likely that these species still occur there. This is because these three species were restricted to areas of native Lupine and the decline and disappearance of these butterfly species was well documented in the few suitable areas available. The lack of recent collections of moths associated with endangered plants or habitats is difficult to use as evidence that the species have been extirpated.
There is also evidence of native butterflies and moths expanding their ranges in recent years. Two Carolinian zone cutworms, Xestia dolosa and Feltia tricosa, were long known to occur in southern Ontario and in eastern Ontario in the Thousand Islands area. Both species expanded their ranges into the Ottawa area and western Quebec in the mid-1970's. Since these species were never collected in the Ottawa area in many years of collecting and are now seen in numbers every year throughout the area, we accept the previous negative evidence and current positive evidence as documenting the northward movement of these species. The situation with the Pearl Crescent butterfly is more difficult to interpret. This species has recently been divided into two species with the "true" Pearl Crescent (Phyciodes tharos) occurring from southern Ontario southward, flying mainly from July to October, and the Northern Crescent (Phyciodes cocyta) occurring throughout Ontario flying mainly in June. A search for tharos in the Ottawa area in 1995 turned up more than 40 colonies, yet there are no tharos among the several hundred cocyta in the Canadian National Collection collected in Ottawa over the past 100 years. It is possible, though it seems unlikely, that the Pearl Crescent has simply been overlooked in Ottawa all these years because it flies later in the season that the much more abundant Northern Crescent. The Olympia Marble (Euchloe olympia) is primarily a prairie species that occurred east to Manitoulin Island; in the past 30 years this butterfly has expanded its range through eastern Ontario and into western Quebec. It is now common in specific sites near Ottawa which had been well studied in earlier years without this species being found. The Common Ringlet (Coenonympha tullia) (Fig. LEP-13) is a boreal zone butterfly that has been expanding its range southwards. It occurred in the Gatineau Hills north of Ottawa but expanded its range into the Ottawa area in the 1950's. In the past forty years it has continued to move southwards and has now reached southern Ontario and southern New England.
