Temporal range: Early Pliocene - Present
|A grasshopper mouse eating a beetle|
Grasshopper mice are rodents of the North American genus Onychomys. Grasshopper mice feed on insects and other arthropods.
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 3.5 to 5.0 inches (8.9–12.7 cm) long body and a tail that is generally 1.0 to 2.5 inches (2.5–6.4 cm) long. Its behavior is rather distinct from other mice.
It is a carnivorous rodent, dining on insects (such as grasshoppers), 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 (scorpions, snakes, etc.). Grasshopper mice do not like bright lights so they generally try to prevent exposure to light; this has allowed for this genus to become nocturnal.
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 (Centruroides sculpturatus). The bark scorpion and the grasshopper mice demonstrate the arms race by coevolving with one another. 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.
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 (which reduces their speed). 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.
Onychomys have six different vocalization types (two neotal and four adult). 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.
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Grasshopper mice tend to have low population densities. They live either alone or in pairs, one male with one female. Very territorial, their average territory size may equal their home range size of about 28 acres.
- Mearns's grasshopper mouse or Chihuahuan grasshopper mouse Onychomys arenicola
- Northern grasshopper mouse, Onychomys leucogaster
- Southern grasshopper mouse, Onychomys torridus
- "Mearns' Grasshopper Mouse (Onychomys Arenicola)." Mearns' Grasshopper Mouse (Onychomys Arenicola). The Mammals of Texas- Online Edition, n.d. Web. 10 Apr. 2013.
- Onychomys: Tiny Terror of the Western Deserts
- Bailey, Vernon; Sperry, Charles (November 1929). "Life History And Habits Of Grasshopper Mice, Genus Onychomys". google scholar. United States Department of Agriculture.
- Rowe, Ashlee H.; Rowe, Matthew P. (November 2, 2015). "Predatory grasshopper mice" (PDF). Current Biology. 25 (21): R1023–R1026. doi:10.1016/j.cub.2015.07.054. ISSN 0960-9822. PMID 26528738 – via CORE.
- Hafner, Mark; Hafner, David (20 February 1979). "Vocalizations of Grasshopper Mice (Genus Onychomys)". Journal of Mammalogy. 60 (1): 85–94. doi:10.2307/1379761. JSTOR 1379761.