Grasshopper mice are rodents of the North American genus Onychomys. Grasshopper mice feed on insects and other arthropods.
Biology
The three species in this genus of New World mice are only distantly related to the common house mouse, Mus musculus. They are endemic to the United States and Mexico. The southern grasshopper mouse has around a long body and a tail that is generally long. Its behavior is rather distinct from other mice. It is a carnivorous rodent, dining on insects, worms, spiders, centipedes, scorpions, snakes, and even other mice. It also stalks its prey in the manner of a cat, sneaking up quietly, and defends its territory by "howling" like a small wolf. The grasshopper mouse is known to be immune to various venoms released by its prey. Grasshopper mice are nocturnal and avoid exposure to bright light.
Ecology
Diet
Grasshopper mice prey on highly venomous arthropods. One example is centipedes that normally kill mice by injecting deadly toxin through their venomous forcipules. Grasshopper mice move swiftly, while centipedes can only inject their toxin if their prey is held by the centipede's needle-sharp claws. The mouse remains out of reach of the centipede, and attacks it by repeatedly biting through its hard exoskeleton. Each attack on the centipede damages its central nervous system, until the centipede is paralyzed and the grasshopper mouse can eat it safely. Another example of a venomous arthropod is the bark scorpion. The grasshopper mouse survives in the deserts of southwest United States by feeding on the bark scorpion, which are plentiful, due to other resources being less common. Their aggressive nature extends beyond their hunting habits: when held in captivity with other mice, they will often kill and eat those other mice. However, they have a disadvantage when it involves capturing in open areas because of their short legs and wide bodies. Fortunately, due to their ability to maneuver well, they are able to move quickly in narrow areas allowing them to capture their prey more efficiently.
Physiology
Pain Intolerance
The bark scorpion and the grasshopper mouse have been coevolving with each other so closely that it has affected their physiology. The scorpion uses its stinger to inject toxins into the nervous and muscle tissues which causes disruption in the animals sensory system. However, as the scorpions stinger evolves to become more toxic, the mice evolve in order to cope with the toxins. Therefore, the grasshopper mice have sensory neurons that have evolved which reject the toxins and prevents pain signals. Researchers now know that the grasshopper mouse barely notices the intensifying sting due to a mutation in the cellular pathway that controls their pain response. Compared to the normal house mouse, the grasshopper mouse has one more amino acid in the protein making up the sodium channel Na+ nav1.8. This change prevents the mouse from processing Na+ currents when injected with the scorpion's venom, which blocks action potential and prevents analgesia. By having a better understanding of the grasshopper mouses's cellular mutation, scientists can conduct more research and eventually develop a pain relieving drug.
Communication
Onychomys have six different vocalization types. They have a wide range of calls that can distinguish them between species, sex, and individuals. For example, the larger mice tend to have deeper voices. When they feel attacked, they will let out a rapid screech/bark.
