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Oddity Ark #78 (258) Southern Grasshopper Mouse

As we near the end of November we come to the request of @arctika, one that shows even the cutest of creatures are able to be monsters. And if you want to request an issue on an amazing animal, fabulous fungus, perplexing plant or awesome paleofauna, don’t hesitate to leave a request in the comments.


Oddity Ark #78 (#258)


Domain: Eukaryota

Kingdom: Animalia

Phylum: Chordata

Class: Mammalia

Order: Rodentia

Family: Cricetidae

Genus: Onychomys

Species: torridus

Related Species: The southern grasshopper mouse is one of the three species within the genus Onychomys, a group known colloquially as ‘howling wolf mice’.

Range: Southern grasshopper mice lives in arid and semi-arid habitats throughout Mexico and the south-western United States.

IUCN Status: The southern grasshopper mouse is currently classified as ‘Least Concern’ by the International Union for Conservation of Nature (IUCN).

Wolf in Mouses Clothing

The southern grasshopper mouse is a small mouse, growing up to 16cm in length and weigh up to 50 grams in weight, with female grasshopper mice larger and heavier than males. Southern grasshopper mice are territorial, with males establishing a territory of 7.8 acres (31565m2) while females establish a territory of 5.9 acres (23876m2) (2). Male southern grasshopper mice are territorial and advertise their presence to other males by howling at night, thus leading to the colloquial name for this species as ‘howling wolf mice’. Southern grasshopper mice have lower population densities then rodents of comparable size, in part due to their territorial nature, and due to the rapid aging of the reproductive system of the species.


The three grasshopper mice species are all obligate carnivores, typically predating upon arthropods, although larger specimens predate upon other rodent species such as the western harvest mouse (Reithrodontomys megalotis). Prey is ambushed from behind and disabled with a quick bite to the neck, although more armoured prey such as the Texan red head centipede (Scolopendra heros) and the Arizona bark scorpion (Centruroides sculpturatus) are typically eaten alive while still striking at their attacker. The neurons of the southern grasshopper mice contain glutamic acid, a chemical that binds with chlorotoxin (C158H249N53O47S11), preventing the rapid firing of the neurons, acting almost akin to an anaesthetic, nullifying the pain from the venom and the struggling of its prey (3). Southern grasshopper mice are predated upon by grey foxes (Urocyon cinereoargentus), western diamondback rattlesnakes (Crotalus atrox) and elf owls (Micrathene whitneyi).


Southern grasshopper mice reach sexual maturity at five months, with gestation lasting approximately forty days. During gestation and when the young have been born, the male gathers food for the female and generally defends his brood. The amount of young born are low in comparison to other similar sized rodents, with a brood of one to five babies being born. Born hairless, by the time they reach twenty days in age, the young are haired, have their eyes open and able to eat solid food. While southern grasshopper mice can live for up to two years, their reproductive systems rapidly age during the first year, with females generally unable to breed in their second year while males go through periods of dormancy in their testicular development.

Ecology 101: A brief guide to Environmental Mechanics #28 - Evolution of Toxin Resistance

A surprising diversity of animals have evolved toxin resistance independently from each other in response to the evolutionary arms race between predator and prey. Toxin resistance comes from chemical immunity within either the nervous system or the circulatory system, depending on which groups of toxins the species is having to be resistant too. Morphological immunities, such as those found in the secretary bird (Sagittarius serpentarius) in the form of hardened scales in the feet, thick plumage and reduced vascular tissue reducing uptake of venom when bitten on the foot while hunting, are not features that grant toxin resistance, but are common features of birds who feed on venomous prey (4).


Animals with toxin resistance fall into four categories; those that feed on venomous prey, those that are predated on by venomous predators, those that engage in toxin scavenging and those that have autoimmunity to their own venom. These categories may overlap, for example Indian cobras (Naja naja), do not only possess an autoimmunity to their own venom, but also resist the venom of other true cobra species (Naja species) and have some resistance to the venom of one their major predators, the king cobra (Ophidiophagus hannah).

Where pit vipers are the most dominant snakes in an environment, animals predated by these snakes, or that predate on them typically have enzymes that denature snake venom metalloproteinases (5), a zinc dependent protein compound within the venom, within their blood streams. These inhibitors denature the metalloproteinases, preventing them from attacking the red blood cells, and causing them to decay within the blood vessels. Examples of species with these enzymes include rock squirrels (Otospermophilus variegatus), European hedgehogs (Erinaceus europeaus) and indigo snakes (Drymarchon couperi); species that are either predated upon by vipers, or in the case of the second two species, actively predate on vipers. These species, even the two mammal species are unrelated and evolved the ability to produce these venom neutralising enzymes independently.

European hedgehog about to predate on a northern viper [5]
European hedgehog about to predate on a northern viper [5]

Neurotoxins contain an array of chemicals including three-finger toxins and a-neurotoxins that target the neurons, which target the sodium and calcium channels causing them to fire continuously, causing pain eventually causing the organs to shut down. Species with resistance to a-neurotoxins typically have the a-1 muscle-type nicotine acetylcholine within their neurons that neutralize the toxins. Animals that make use of neurotoxins are typically more common than hemotoxins, and a wider range of species have resistance to this toxin group including the mongoose family, central bearded dragon (Pogona vitticeps), honey badger (Mellivora capensis) and even fish such as the three spined stickleback (Gasterosteus aculeatus). The later species appears to have developed this resistance to endure chemical release by cyanobacteria blooms (6).


Toxin resistance is a trait that can be lost if the animal that possesses it does not require the protection from the venom. Genetic studies of the northern viper (Viper berus) shows that the species has reversed its immunity to a-neurotoxins. This is generally because, throughout its range, the northern viper does not compete with snakes that have neurotoxic venom and as such the need for protection is not required (7). Toxin resistance is costly to maintain and without the pressure of venomous predation or targeting venomous prey, and without this pressure it more costly to keep the resistance then losing it.



2. Frank, D. H., & Heske, E. J. (1992). Seasonal changes in space use patterns in the southern grasshopper mouse, Onychomys torridus torridus. Journal of Mammalogy, 73(2), 292-298.

3. Thompson, Bemjamin (2018). "The Grasshopper Mouse and Bark Scorpion: Evolutionary Biology Meets Pain Modulation and Selective Receptor Inactivation" (PDF). Journal of Undergraduate Neuroscience Education. p. R51-R53

4. Portugal, S. J. , Murn, C. P. , Sparkes, E. L. & Daley, M. A. (2016). The fast and forceful kicking strike of the secretary bird. Current Biology 26, 58–59

5. Ferraz, C. R. , Arrahman, A. , Xie, C. , Casewell, N. R. , Lewis, R. J. , Kool, J. & Cardoso, F. C. (2019). Multifunctional toxins in snake venoms and therapeutic implications: from pain to hemorrhage and necrosis. Frontiers in Ecology and Evolution 7, 1–19.

6. Aráoz, R. , Molgó, J. & Tandeau de Marsac, N. (2010). Neurotoxic cyanobacterial toxins. Toxicon 56, 813–828.

7. Khan, M. A. , Dashevsky, D. , Kerkkamp, H. , Kordis, D. , de Bakker, M. A. G. , Wouters, R. , van Thiel, J. , Op den Brouw, B. , Vonk, F. , Kini, R. M. , Nazir, J. , Fry, B. G. & Richardson, M. K. (2020). Widespread evolution of molecular resistance to snake venom alpha‐neurotoxins in vertebrates. Toxins 12, 1–20.

Picture Credits

1. 5984f008155e0.image.jpg (1200×817) (

2. GrasshopperMouse-BDTAY7.jpg (2400×1601) (

3. rowe4.jpg (1374×917) (

4. R.e5d97e69cb3eb8e2bd3e692d47c5f539 (739×924) (

5. ffa4536163b020e8860e3491e29355aa--hedgehogs-snakes.jpg (736×482) (

6. full (2048×1365) (

Next week we have something that morphs and shifts into multiple forms as it grows and mutates. And if you want to see more amazing animals and plants, please check out the Oddity Arkive or past issues. And if you want even more animals, please check out dearly departed Impurest Cheese’s Guide to Animals which can be found here, or on the blog of the lycanthrope @ficopedia

If you want a chance to choose the topic of the last issue of the year, click here to vote in a poll regarding this year’s Seasonal Special

If you still have a yearning for learning, please check out the master list of Mr Monster’s Martial Arts Journey.