Southern grasshopper mouse

In the arid regions inhabited by the southern grasshopper mouse, the Arizona bark scorpion is plentiful and avoided by most predators because of the very painful sting it can inflict. The grasshopper mouse can feed on this scorpion with impunity even when the scorpion stings it repeatedly in the face. Researchers have found that a neural mechanism is involved that blocks the sending of pain messages to the brain. This mouse can normally feel pain from other sources, but can be temporarily insensitive to these stimuli after a dose of venom from a bark scorpion. This pain modulation is activated soon after the scorpion sting; the mouse does briefly feel pain from the sting, but the scorpion venom binds to the transmembrane channel otNav1.8. Specifically, the venom binds to a glutamic acid residue located within the channel protein, thus preventing neuron action potentials from firing and acting as a type of temporary anesthetic and pain reliever for the mouse. When this glutamic acid was replaced with hydrophilic glutamine residue, the venom did not bind with the protein, and the pain modulation ability was lost.

Females are able to produce several litters in a year, but their reproductive life does not usually last into their second year. The average litter size is 2.6 (range 1 to 5), produced after an average gestation period of 29 days. The young are born naked, with pink translucent skin. One day later the pigment is developing on the dorsal surface and by day ten, hairs 3 millimetres (0.12 in) long are present on the back. The eyes open on day 15 and solid food is being consumed by day 19. The females give birth to their first litter when four or five months old.

Southern grasshopper mice are unique among other North American rodents in the family Cricetidae in that their diet consists mostly of arthropods. They are usually found in areas with lower population densities. Several studies have demonstrated that the reproductive attributes of this species allows them to be naturally maintained at lower population densities. Females tend to be sexually active only during one breeding season, which is due to their rapid reproductive aging following their first year. Moreover, males' unique pauses in their testicular activity during the breeding season might also contribute to the lower population densities in which they live.

The natural habitat of southern grasshopper mice include hot, arid valleys, and scrub deserts. A male and female along with their offspring occupy a larger home range for burrowing compared to males and females alone. On average, males have a home range of 7.8 acres, while females occupy an area of 5.9 acres. They tend to maintain a specific place of residency for a longer period of time compared to other mammals. The home ranges between southern grasshopper mice are not too far from each other, with an average maximum distance of 118.4± 8.0 meters. However, adults males tend to be very territorial and their efficient spacing is facilitated by vocalizations they make at night.

In a study done by Denise H. Frank and Edward J. Heske, the home range of southern grasshopper mice in the Chihuahuan Desert were observed. The home range of males during the non-breeding season were found to be smaller than those held by males during the breeding season. In contrast, there was not a significant difference between the home ranges of females during the breeding and non-breeding seasons. Male ranges during the reproductive season were some two to three times larger than those of adult females during the reproductive season.

There are no currently known conservation issues associated with southern grasshopper mice, largely due to its wide distribution and tolerance for disturbances caused by arthropods. However, some disturbances have been observed in their low density populations. Many more population studies will need to be performed in order to gain further insight into the conservation status of this species.