Distribution

Centruroides spp.: southern USA to Mexico and Central America, including the Caribbean, and parts of northern South America. Largest variety of species in Mexico.

Medically important species:

1. Mexico: Guerrero, Jalisco, Nayarit, Oaxaca, Michoacan, Las Tres Marias Islands, Sinaloa;
2. USA: Arizona, western New Mexico, southern California along the Colorado river (further spread to the area of Los Angeles is feared), southern Nevada (coastal region of Lake Mead); Mexico: Baja California, Sonora;
3. Mexico: Aguascalientes, Colima, Guanajuato, Jalisco, Michoacan, Oaxaca, Sinaloa, Veracruz;
4. Mexico: C. l. limpidus: Guerrero, Michoacan, Mexico, Morelos, Oaxaca, Puebla; C. l. tecomanus: Colima, Jalisco;
5. Mexico: Nayarit, Jalisco and southern Sinaloa;
6. Mexico: Sinaloa, Sonora; 
7. Mexico: Durango, Zacatecas.

Fig. 4.35 Centruroides noxius

Map 3. Distribution of Centruroides species with medical significance.

Biology

Slender pincers and narrow tail. Body length of C. exilicauda approx. 5–7 cm, C. suffusus 8–9 cm, C. noxius barely more than 5 cm, C. elegans up to 8 cm, C. limpidus up to 7 cm. Several other species up to more than 10 cm. Colouring variable, from light shades of yellow or brown to red-brown and dark-brown. Sometimes dorsal body markings in the form of two dark longitudinal stripes.

Nocturnal. As the name "Bark scorpions" suggests, these scorpions like to live under loose bark or in crevices in trees or fence posts. They do not burrow into the ground as many other scorpions do. The fact that they live above ground may be a reason why Centruroides species are closely associated with the living areas of humans in many regions in which they are found. They are known to hide themselves outside houses in woodpiles or under planks of wood or rubbish. They also often enter houses, where at night they hunt prey on the walls and ceilings and during the day hides themselves wherever they can find dark, narrow niches.

Risk

Within this genus there are great differences with regard to the dangerousness of individual species. Besides the medically most significant members listed here, there are several other species whose stings barely cause more than local symptoms. An example of this is the widespread species C. vittatus. In the USA, where this species is found in the southern states of Texas and Florida, no serious accidents due to scorpions have been documented in these areas. The only dangerous species that can lead to serious accidents in the USA is C. exilicauda (Stahnke 1972, Russell and Madon 1984). However most accidents caused by this species are minor and generally only children under 5 years are at serious risk (Likes et al. 1984).

In Mexico scorpion stings are a major medical problem. Cases of serious envenoming are almost always caused by members of the genus Centruroides. Although the mortality rate has decreased dramatically from the 1940s to the present, through better medical care and increased use of antivenom, the incidence of scorpion envenoming is still high, with an estimated 250,000 cases each year (Alagon et al. 1999). Most accidents occur in living quarters in regional areas, but some species also cause large numbers of stings in various cities.

Compiled data from Mazzotti and Bravo-Becherelle (1963) document an average fatality rate for Mexico of 1,775 per year (7.9 per 100,000 inhabitants) between 1940 and 1949. In the years 1957 and 1958, this rate did undergo a marked decrease, with 1,495 and 1,107 deaths, respectively (4.7 and 3.4 per 100,000 inhabitants, respectively), but these data still indicate a serious problem. 81.7% of the fatalities were children under 5 years, and a further 12.6% were children between 5 and 9 years. The most severley affected regions were Colima, Nayarit, Guerrero and Morelos, with an average annual mortality rate of 83.7, 41.6, 41.5 and 37.3 per 100,000 inhabitants, respectively. In the same periods of 1940–1949 and 1957–1958 around 10 times fewer people died of snakebites in Mexico. In the Mexican Red Cross Hospital in Leon (Guanajuato), 38,068 people were admitted with scorpion envenoming between 1981 and 1986. C. infamatus infamatus was considered responsible for the great majority of these cases. Not a single patient died, which can be attributed to the prompt administration of antivenom in the severe cases (Dehesa-Davila 1989).

There are no known cases of serious scorpion envenoming from Central America. Accidents due to C. margaritatus are not uncommon in Colombia, but it appears that these stings barely cause more than local symptoms (Marinkelle and Stahnke 1965, cited in Keegan 1980). According to more recent investigations in Colombia, C. gracilis, along with several Tityus species, has been held responsible for cases of moderate to severe, life-threatening envenoming (Gomez and Otero 2007).

Literature (biological)

Fet et al. 2000, Keegan 1980, Stahnke 1972, 1978, Stahnke and Calos 1977, Najera 1975, Sissom 1990, Franke and Stockwell 1987, Baerg 1961

The Scorpion Files

The Scorpion Fauna

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