Satyrium semiluna

Half-Moon Hairstreak Butterfly

The half-moon hairstreak butterfly is a small grassland butterfly found in Western North America. There is a lot that we do not know about this species, so much of our work is about unravelling those mysteries.

The situation

What is threatening the hairstreak?

The only population of the half-moon hairstreak in Alberta is found on the Blakiston Fan in Waterton Lakes National Park, more than 450 kilometres from other populations. The presence of spotted knapweed (Centaurea stoebe), an invasive plant species, is thought to be a threat to the butterfly as it competes with native vegetation that the half-moon hairstreak relies on for food. Natural disasters such as flooding, or fires could also be detrimental to this population. The Waterton population suffered a severe decline in 2018, which was caused by the 2017 Kenow wildfire that burned more than 50% of the half-moon’s habitat.

Our work

Working with our partners, we are monitoring the half-moon hairstreak population and exploring conservation actions. Future recovery strategies could include conservation breeding, restoring habitat, and managing invasive plants. We are working to better understand the life history of this butterfly, its behaviours, interactions with other species, and survival rates.

Our conservation impact

By gaining more insight about this sensitive species, we aim to enhance the population of half-moon hairstreak in Waterton Lakes National Park and to contribute useful information for better management planning.

Did you know?

The half-moon hairstreak has several lookalikes such as the Melissa blue and the Boisduval blue butterflies, but it can be distinguished, while at rest, as it does not open and close its wings when perched on a plant.

The half-moon hairstreak, like many Lycaenid butterflies, has a special relationship with ants. The butterfly larvae will secrete a sugary substance that will attract and feed the ant and in return, the ant will protect the larvae from other predators.


We are grateful for the collaboration and support of the following partners in helping conserve the half-moon hairstreak in Alberta.

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