One special invertebrate that calls Waterton Lakes National Park home is the endangered half-moon hairstreak butterfly.

An aerial image of a section of Waterton Lakes National Park with a graphic overlay showing the Blakiston Fan grassland area with reference to the Park Gate, Entrance Road, Red Rock Parkway and Prince of Wales hotel
Location: Blakiston Fan

This small, brown butterfly is known to exist in nine locations in Canada: eight in British Columbia and only one in Alberta, in Waterton Lakes National Park on a grassland area known as the Blakiston Fan.

This butterfly has black spots with white rings around them on its wings. Male half-moon hairstreaks have a wingspan of approximately 25 mm (about the size of a loonie). Females have larger and paler wings than the males.

The half-moon hairstreak's eggs are greenish white, and the caterpillar is light green with whitish lateral chevrons and a dark brown head.

Fun facts
  • The half-moon hairstreak that calls Waterton Lakes National Park home is unlike many other species of hairstreaks, it has no “tail” on the hindwing.
  • Butterflies are important to the ecosystem, both as a prey species and a pollinator. A diverse population of butterflies can indicate that an ecosystem is healthy and flourishing.

Why the half-moon hairstreak matters

A scientist on the Blakiston Fan with a butterfly net
Waterton Lakes National Park is the only location where this butterfly is known to live in Alberta

Species at risk

In 2006, the half-moon hairstreak butterfly was listed as an endangered species under the Species at Risk Act (SARA). This means that Parks Canada gives it special attention in Waterton Lakes National Park.

The Blakiston Fan, the butterfly's only known home in Alberta, was listed as Critical Habitat in 2016. This habitat is an alluvial fan consisting of dry grasslands on soils that drain quickly. The area is subject to flooding.

Species at risk in Waterton Lakes National Park

A 2018 survey indicated the Waterton Lakes population of the half-moon hairstreak butterfly has experienced a serious decline.

This decline may be due to habitat destruction caused by invasive plants like spotted knapweed. The population of half-moon hairstreaks in Waterton Lakes is threatened by these invasive plants that compete with native plants, necessary for the butterfly’s survival.

Natural disasters such as floods and fires can also be devastating to this isolated population.

Wild about wildflowers

A half-moon hairstreak butterfly on a flower
Waterton's wildflowers are vital to the half-moon hairstreak’s survival

Wildflowers are important to all stages of the half-moon hairstreak's life.

Silky and silvery lupine wildflower species are essential for breeding. Half-moon hairstreaks lay eggs on lupines in the summer months. When the caterpillars hatch the following spring, their main food source is that same lupine.

Nectar from plants such as yellow buckwheat and Missouri goldenrod are other important food sources.

Caterpillars transform once again to emerge as adult butterflies. Adults only live for six to 14 days. Males are more active than females, searching for a mate and patrolling and defending high shrubs in their environment.

What Parks Canada is doing to help the half-moon hairstreak

A Calgary Zoo expert monitoring a half-moon hairstreak butterfly in Waterton Lakes National Park
Parks Canada and the Calgary Zoo are working together on a program to conserve and restore the half-moon hairstreak

Parks Canada is working with the Calgary Zoo to understand this small insect and what will best help it survive. They are sharing knowledge and conservation techniques to help protect and restore the amazing half-moon hairstreak butterfly.

This program will greatly improve understanding of the secretive life history of the half-moon hairstreak. Researchers and Parks Canada want to better understand the butterfly’s different life stages, survival rates, behaviour and how they interact with other species. This will help determine conservation actions and management practices.

Other conservation actions include assessing and restoring the butterfly’s habitat, and managing invasive plants.

How you can help
Parks Canada and Calgary Zoo staff monitoring butterflies on grasslands in in Waterton Lakes National Park
Volunteering is a great way to help protect the half-moon hairstreak butterfly
Play Clean Go
Clean equipment such as boots, bikes, canoes, kayaks, paddleboards and also pets before arriving in the park, to prevent the spread of invasive plants and animals.
Leave No Trace
Stay on roads, paths and marked trails when hiking, and take extra care to not crush or pick any plants.
Become a habitat hero! Volunteer to remove harmful invasive plants from the park.