Mammals
Northern Grasshopper Mouse
Onychomys leucogaster · also called scorpion mouse
Somewhere on the shortgrass prairie at night, a mouse stands on its hind legs, tips its head back, and howls. Then it goes hunting for scorpions. The northern grasshopper mouse is one of the few rodents that is a predator first and a mouse second.
Overview
Onychomys leucogaster lives in the grasslands, sagebrush, and deserts of central and western North America. Around 90 percent of its diet is animal matter — grasshoppers, beetles, scorpions, centipedes, and other rodents — killed with a fast bite to the head. It is stocky, short-tailed, and strong-jawed, built more like a small carnivore than a mouse.
The howl
It rears up, points its nose skyward, and gives a long, thin whistle that carries across open ground, used to defend a large territory — often several hectares held by a monogamous pair.
Scorpion eater
It hunts the Arizona bark scorpion, one of North America’s most venomous. A modified pain channel in its nerves means the venom acts as a painkiller instead of causing pain, so the mouse can take repeated stings and keep eating.
Status
Least Concern and widespread, but always at low density because each pair needs a big hunting territory. Rather than dig, it usually takes over another animal’s burrow.
Northern Grasshopper Mouse: common questions
Does the grasshopper mouse really howl?
Yes, though howl is a loose description of a small, high sound. The mouse rears onto its hind feet, throws its head back, opens its mouth wide, and emits a sustained, almost bird-like whistle lasting a second or more, at a frequency people can just hear. Recordings and lab studies show it functions like the howl of a wolf or the song of a gibbon, as a long-distance signal that announces the caller's presence and marks its territory, often given before or after a hunt and answered by neighbours. For an animal the size of a house mouse to broadcast a territorial call across open desert is genuinely unusual.
How can it eat a bark scorpion without being hurt?
The Arizona bark scorpion's venom normally causes intense, radiating pain by forcing open sodium channels on pain-sensing nerves. In the grasshopper mouse, one of those channels is shaped slightly differently, so the venom toxin binds to it and blocks it instead of activating it. The effect is that a sting briefly numbs the mouse rather than hurting it. In tests, grasshopper mice injected with bark scorpion venom licked the site for a moment and then behaved normally, and could be stung several times during a fight and still kill and eat the scorpion. The mouse typically bites off or disables the stinger early in the attack anyway.
Is it dangerous to have grasshopper mice around, or are they pests?
They are not household pests and are not a problem for people. Grasshopper mice live in open natural country, not in buildings, they occur at low densities because of their large territories, and they do not hoard grain or gnaw structures the way house mice and rats do. If anything they are beneficial, since a large part of their diet is insects that damage rangeland and crops, along with other rodents. They are difficult to keep in captivity and are not kept as pets, partly because of the specialised live-prey diet and the territorial, aggressive temperament.
What is the difference between the northern and southern grasshopper mouse?
They are two closely related species that divide the arid interior of North America between them. The northern grasshopper mouse is the larger and more northerly, found from the Canadian prairies down through the Great Plains and Great Basin, in cooler grassland and shrub-steppe. The southern grasshopper mouse is smaller and occupies hotter, lower deserts of the southwestern United States and Mexico, including the range of the Arizona bark scorpion, and it is the one most studied for venom resistance. Both are carnivorous, both howl, and both take over other animals' burrows; where their ranges meet they tend to sort out by habitat.