Grasshopper Glacier, Ancient glacier in Beartooth Mountains, Montana.

Grasshopper Glacier is a glacier in the Beartooth Mountains of Custer National Forest, Montana, within the Absaroka-Beartooth Wilderness. It begins above 11,300 feet (3,400 m) and measures about 0.20 miles (0.32 km) long and 0.25 miles (0.40 km) wide. Since 2007 it has consisted of several smaller glaciers, each in a north-facing cirque. Its ice holds layers of white and pale blue-green, with bands of sediment and compressed ice.

A geologist discovered the ice mass in the early 1900s and recognized frozen insects within it. Since then, scientists have examined this glacier to learn about insect species that once lived in this mountain region.

The name refers to the tens of millions of grasshoppers entombed in the ice, some hundreds or thousands of years old. Early researchers sent specimens to entomologists, who identified the extinct Rocky Mountain locust (Melanoplus spretus). The insects are thought to have been caught in severe storms. Since the late 1980s, lower snowfall and higher temperatures have melted many specimens before they can be retrieved.

Access requires a high-clearance vehicle for the initial route and then additional hiking beyond that point. The access road is closed for most of the year and only open during the brief summer season.

Millions of grasshoppers have been frozen within the ice over the centuries, making it a natural archive of insects. These preserved specimens come from a time when a specific locust species was common in the region.