Smeringurus mesaensis, the dune scorpion, is native to the Nearctic region. It is a common scorpion species in the southwestern United States in the southern half of California and Arizona. It is also present in Mexico, particularly in Baja California. (Haradon, 1983)
The scorpion body can be divided into the front cephalothorax and the abdomen. The cephalothorax is covered dorsally by the carapace. A pair of median eyes can be found in the front center of the carapace and lateral eyes are found on each side of the carapace. The pedipalps are modified into large structures ending in claws, one of the more significant scorpion features. They have four pairs of legs. The abdomen can be divided into the anterior mesosoma, and the posterior metasoma, or tail. The mesosoma has 7 segments, each covered dorsally by a plate. The metasoma consists of 5 segments, ending in the stinger. Pectines, comb-like sensory structures, are found on the ventral side near the middle of the body. Smeringurus mesaensis is a sandy beige color, so light that it often appears slightly translucent. The dorsal plates are a darker brownish-grey, and the joints and portions of the pedipalps may be darker. On average, dune scorpions are 72 mm in length and weigh 2 g. In this species, females are usually larger than males, although males have larger pedipalps and older males have longer pectines than females. (Hjelle, 1990; Polis and Farley, 1979; Polis and Sissom, 1990; Polis, 1980)
After eggs are fertilized during mating, they develop internally in females for 10 to 14 months. Live births take place between July and September. After birth, Smeringurus mesaensis offspring climb aboard the back of their mother, until their first molt, which occurs about 12 days later. The juveniles then disperse and undergo 6 molts over the next 19 to 24 months. After their final molt, they reach adulthood. (Polis and Sissom, 1990)
Mating takes place in August and September, usually on moonless nights. Smeringurus mesaensis has a long courtship dance. During mating season, males become erratic and spend a significantly increased amount of time on the surface, out of their burrows. They travel long distances, become skittish, and feed less. Vibrations are used to find mates, as receptive females can detect the vibrations of nearby males. In this species, females also produce pheromones to attract mates and they initiate courtship. A female approaches a male and “attacks” him repeatedly by quickly approaching him and clubbing him with her tail, with the stinger tucked away. They both back away and the male “judders” by rocking back and forth rapidly with his legs and pectines spread out. Juddering may be a way for the female to identify the male as a conspecific. The female attacks again and the sequence repeats, again and again, until the male grasps the female for the mating dance. His pedipalps grip her pedipalps, and he leads her in search of a substrate to deposit the spermatophore. This promenade can last from 5 to 35 minutes, and the pair can move a few meters or as far as 25 meters. During this time, the male massages the female's chelicerae with his own chelicerae. The female becomes more cooperative and less aggressive during the massage. The male's pectines are spread throughout this time, likely aiding chemoreception and pheromone detection. When the male finds a suitable spot, he scrapes the sand with his legs, maybe clearing a spot, and secretes the spermatophore upon a surface such as a stick. The spermatophore stands upright, and he pulls the female over it. She lowers herself and her operculum opens, taking up the sperm. After a few seconds, sperm transfer is complete, and she does a “handstand”, by tilting forward. As soon as this is done, the male abruptly disengages, usually by stabbing the female with his metasoma, and tries to make a quick getaway. Sometimes, he manages to run free, while the female stands and sways, likely aiding sperm travel in her reproductive system. Other times, however, the female catches the male, envenomates him with her sting, and cannibalizes him. Males may perform behaviors such as the cheliceral massage to calm the female, due to the threat of cannibalism. If the male survives, he is able to mate again with other females. (Polis and Farley, 1979; Polis and Sissom, 1990; Warburg and Polis, 1990)
Dune scorpions are viviparous, so after mating, the fertilized eggs are carried internally by the female for 10 to 14 months. Embryonic development does not proceed while females are inactive during winter months. Births occur between July and September, and are very synchronized from year to year. The female takes cover to give birth, usually in her burrow. She elevates the front of her body, arches her metasoma, flexes her palps, and flexes her legs underneath her body to form a "birth basket". The genital operculum opens, and the young emerge one at a time and fall into the "basket". This species is born covered in a membrane and must wriggle free. When they are free, they climb up the legs of the female and onto her back. They remain there until their first molt, in about two weeks. On average, the litter size is about 33, but can by anywhere from 9 to 53 individuals. Smeringurus mesaensis reaches maturity in 19 to 24 months. This species is iteroparous, and have been observed producing at least two litters, each a year apart. (Polis and Sissom, 1990; Polis, 1980)
Females exhibit significant parental care. The female's ova contain yolk to provide nourishment for the offspring, and they receive additional nourishment from the mother during gestation. At birth, the female loses 43% of her body weight, emphasizing the extent of her investment. Once the young are born, they climb onto her back and remain there until their first molt, which occurs about 12 days later. During this time, the young do not feed, but they do uptake water from their mother. This post-birth association has been shown to be necessary, as young scorpions that are taken away from their mother do not survive. The bond is maintained by chemoreception, as the young are able to identify conspecific female scorpions. After the first molt, the young disperse, and all maternal behavior stops. The female may even act predatory towards her young if they do not leave at this time. (Polis and Sissom, 1990)
Smeringurus mesaensis is fossorial and spends much of its time in burrows that it digs. It is estimated that 92 to 97% of its life is spent in these burrows. The burrow keeps it safe from predators and provides a consistent environment, away from the harsh extremes and dry conditions of the desert. Dune scorpions emerge from their burrows to hunt and mate. They are nocturnal and emerge around dusk, spending an average of 4 hours on the surface. Adults are active earlier in the evening, while younger scorpions are active later in the evening. Activity on the surface is also seasonal, as dune scorpions are more active during mating season and during times of high prey availability. Males are especially active during mating season, moving large distances while searching for mates. Adults are solitary in their burrows, but young instars may aggregate shortly after dispersing from their mother's burrow. Smeringurus mesaensis is very aggressive, especially towards other scorpions and cannibalism is common. These scorpions become inactive during the winter. (McCormick and Polis, 1990; Polis and McCormick, 1987; Polis and Sissom, 1990; Polis, 1990; Warburg and Polis, 1990)
Dune scorpions spend much of their time in burrows. At night, they come to the surface to hunt. These scorpions have remarkably good homing behavior. They have been spotted relatively long distances from their burrow, up to 8 meters away, only to return to the same burrow that night. Because of this, they largely remain in the same general area. However, during mating season, males are much more active, moving large distances every night, as much as 100 meters, essentially becoming nomadic during this time period. (Polis and Sissom, 1990; Polis, 1990)
Dune scorpions gain most of their information about the environment by detecting vibrations in the sand and substrate. They have slit sensilla in their legs, as well as sensory hairs on their tarsi. These mechanoreceptors allow them to determine the direction and distance of the vibration's source, as well as whether the source is above or below ground. These scorpions assume a stance with all 8 legs arranged in a circle, with each tarsi perpendicular to the substrate, and are able to detect vibrations from up to 50 cm away. In response to a vibration, they quickly turn and orient themselves in the direction of the source. This allows them to find prey and mates. Females also use pheromones to attract mates. Pectines are comb-like structures located on the ventral side of the abdomen that function as chemoreceptors. During the courtship dance, male's pectines are usually spread out and continually sweep the surrounding substrate. A tactile connection is maintained between the male and the female throughout most of the courtship dance and mating, as the male holds onto the female and leads her, massaging her chelicerae. Chemoreception is used by recently birthed young to identify conspecific adult females. Vision is weak, as Smeringurus mesaensis is nocturnal, but it likely does use vision to orient itself at night by using stones or shadows, allowing it to travel several meters away from its burrow and find its way back. It can also likely use polarized light to orient itself as well. Increasing amounts of light as morning approaches is a visual cue for the scorpion to burrow for the day. (Brownell and Farley, 1979; Brownell, 2001; Hill, 2009; Hjelle, 1990; Polis and Sissom, 1990; Polis, 1990; Warburg and Polis, 1990)
Smeringurus mesaensis is carnivorous, and primarily feeds upon insects and other arthropods. It has a huge variety of prey items, with over 125 prey species recorded. It is a sit and wait predator, and sits motionless in the mouth of its burrow, waiting for a prey item to move past. When it catches the prey, it stings the prey and paralyzes it with venom, at which point the scorpion can easily feed. It feeds on arachnids, millipedes, centipedes, terrestrial isopods, solifuges, and a large variety of insects. These scorpions cannibalize smaller adults and young instars, likewise, females often cannibalize males after mating. Smeringurus mesaensis may also prey on other scorpion species. Larger dune scorpions have been observed feeding on small snakes such as <<Leptotyphlops humilis, and likely feed on other small or juvenile reptiles. (McCormick and Polis, 1990; Polis, 1980; Warburg and Polis, 1990)
Predators of Smeringurus mesaensis include small mammals such as grasshopper mice and birds including owls, as well as lizards, frogs, toads, snakes, arachnids, centipedes, and some insects, mainly ants. Cannibalism and intraguild predation are also a large threat for dune scorpions. To defend itself against predators, S. mesaensis spends much of its time safely in its burrows. They also have a venomous sting, which may be used for defense, though it is primarily used to paralyze prey. The thick and powerful pedipalps, primarily used for digging, can also be used as defense. Young instars that have recently dispersed from their mother's care are most susceptible to predation and often aggregate to appear larger and more threatening. (McCormick and Polis, 1990; Polis and Farley, 1979; Polis, 1980; Polis, 1990)
Smeringurus mesaensis is often the most dominant scorpion species in the areas it inhabits, with densities as high as 1,300 to 4,000 individuals/ha. At such high densities, they can be significant predators, with their predation effecting other populations. Intraguild predation and cannibalism are very common for dune scorpions. Removing Smeringurus mesaensis from an area often leads to other scorpion populations increasing as a result. Smeringurus mesaensis is prey to a variety of desert animals including small mammals, birds, lizards, snakes, spiders, and other scorpions. It can also host the ectoparasitic mite, Pimeliaphilus joshuae. (McCormick and Polis, 1990; Polis and McCormick, 1987)
Dune scorpions can be kept as pets. They should be kept in an enclosure like an aquarium, with a burrowing substrate, and can be fed insects. It is strongly advised that dune scorpions are kept alone in their enclosure. ("Smeringurus mesaensis care", 2008)
Smeringurus mesaensis is venomous, and uses the venom in its tail to sting and paralyze prey. The venomous sting can also be used for defense, and may sting humans when threatened or disturbed. Those that keep dune scorpions as pets are advised not to handle them, and owners have compared the scorpion stings to hornet stings. ("Smeringurus mesaensis care", 2008; McCormick and Polis, 1990)
Smeringurus mesaensis has no special conservation status.
Smeringurus mesaensis is also known as Paruroctonus mesaensis. Smeringurus is a relatively new genus and much of the literature concerning this species can be found under Paruroctonus. All scorpions including dune scorpions fluoresce under UV light. This is an easy way to find and observe them at night when they are active. (Brownell and Polis, 2001; Haradon, 1983)
Angela Miner (author), Animal Diversity Web Staff, Leila Siciliano Martina (editor), Animal Diversity Web Staff.
living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
an animal that mainly eats meat
uses smells or other chemicals to communicate
in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
parental care is carried out by females
union of egg and spermatozoan
Referring to a burrowing life-style or behavior, specialized for digging or burrowing.
having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.
the state that some animals enter during winter in which normal physiological processes are significantly reduced, thus lowering the animal's energy requirements. The act or condition of passing winter in a torpid or resting state, typically involving the abandonment of homoiothermy in mammals.
An animal that eats mainly insects or spiders.
fertilization takes place within the female's body
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.
having the capacity to move from one place to another.
the area in which the animal is naturally found, the region in which it is endemic.
active during the night
the business of buying and selling animals for people to keep in their homes as pets.
chemicals released into air or water that are detected by and responded to by other animals of the same species
light waves that are oriented in particular direction. For example, light reflected off of water has waves vibrating horizontally. Some animals, such as bees, can detect which way light is polarized and use that information. People cannot, unless they use special equipment.
breeding is confined to a particular season
remains in the same area
reproduction that includes combining the genetic contribution of two individuals, a male and a female
uses touch to communicate
that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).
Living on the ground.
an animal which has an organ capable of injecting a poisonous substance into a wound (for example, scorpions, jellyfish, and rattlesnakes).
movements of a hard surface that are produced by animals as signals to others
uses sight to communicate
reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.
2008. "Smeringurus mesaensis care" (On-line). ScorpionForum. Accessed January 03, 2014 at http://www.scorpion-forum.com/t911-smeringurus-mesaensis-care.
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Brownell, P., R. Farley. 1979. Detection of Vibrations in Sand by Tarsal Sense Organs of the Nocturnal Scorpion, Paruroctonus mesaensis. Journal of Comparative Physiology, 131: 23-30.
Brownell, P., G. Polis. 2001. Introduction. Pp. 3-12 in P Brownell, G Polis, eds. Scorpion Biology and Research. New York, New York: Oxford University Press.
Gefen, E. 2008. Sexual dimorphism in desiccation responses of the sand scorpion Smeringurus mesaensis (Vaejovidae). Journal of Insect Physiology, 54/5: 798-805.
Haradon, R. 1983. Smeringurus, a New Subgenus of Paruroctonus Werner (Scorpiones, Vaejovidae). Journal of Arachnology, 11/2: 251-270.
Hill, P. 2009. How do animals use substrate-borne vibrations as an information source?. Naturwissenschaften, 96/12: 1355-1371.
Hjelle, J. 1990. Anatomy and Morphology. Pp. 9-63 in G Polis, ed. The Biology of Scorpions. Stanford, California: Stanford University Press.
McCormick, S., G. Polis. 1990. Prey, Predators, and Parasites. Pp. 294-320 in G Polis, ed. The Biology of Scorpions. Stanford, California: Stanford University Press.
Polis, G. 1980. The effect of cannibalism on the demography and activity of a natural population of desert scorpions. Behavioral Ecology and Sociobiology, 7/1: 25-35.
Polis, G. 1990. Ecology. Pp. 247-293 in G Polis, ed. The Biology of Scorpions. Stanford, California: Stanford University Press.
Polis, G., R. Farley. 1979. Behavior and Ecology of Mating in the Cannibalistic Scorpion, Paruroctonus mesaensis Stahnke (Scorpionida: Vaejovidae). Journal of Arachnology, 7/1: 33-46.
Polis, G., S. McCormick. 1987. Intraguild Predation and Competition among Desert Scorpions. Ecology, 68/2: 332-343.
Polis, G., W. Sissom. 1990. Life History. Pp. 161-223 in G Polis, ed. The Biology of Scorpions. Stanford, California: Stanford University Press.
Warburg, M., G. Polis. 1990. Behavioral responses, rhythms, and activity patterns. Pp. 224-246 in G Polis, ed. The Biology of Scorpions. Stanford, California: Stanford University Press.