Scorpions (Scorpiones): Taxonomy & Venomous Species

Chapter 23
Scorpions (Scorpiones)
Gary R. Mullen
1
and W. David Sissom
2
1
Department of Entomology and Plant Pathology, Auburn University, Auburn, AL, United States;
2
Department of Life, Earth and Environmental
Sciences, West Texas A&M University, Canyon, TX, United States
Scorpions represent an ancient group of arachnids that
first appeared in the Silurian Period in the fossil record.
They are believed by many arachnologists to be related
to the now-extinct eurypterids, large chelicerates that
lived in estuaries and coastal lagoons from the Ordovician
Period through the Permian Period. Except for their
smaller size, scorpions are notably similar in appearance
to fossilized marine scorpions of the Silurian and
Devonian. They probably first crawled onto land as air-
breathing arachnids during the late Devonian and early
Carboniferous 325e350 million years ago. Throughout
recorded history scorpions have intrigued human cultures,
being revered and attributed special powers by some
and feared as sinister and ominous by others. Scorpion
images appear as religious symbols; on seals, magical
tablets, amulets, and boundary stones; and in the origin
stories of ancient civilizations such as the Chaldeans
and Egyptians. They also figured prominently in Greek
mythology and as one of the 12 constellations or signs of
the Zodiac.
Despite the many superstitions and misconceptions
about scorpions that persist to this day, their reputation as
dangerously venomous arthropods is generally overstated.
Most scorpions are not aggressive and inflict only minor,
transient pain and discomfort when they do sting, typically
to defend themselves when threatened. There are, however,
40e50 species worldwide that pose significant health
problems. About 25 species are considered to be capable of
causing human deaths. Most of them occur in the Tropics
and Subtropics or in arid regions of temperate zones.
TAXONOMY
Scorpion taxonomy has been unstable since the turn of
this century. In his review of scorpion classification,
Sissom (1990) listed 1,077 species, 117 genera, and nine
families. During the 1990s, many new families were
proposed that helped to create a clearer picture of phylo-
genetic relationships among the genera of scorpions. In
their catalog of the scorpions of the world, Fet et al. (2000)
listed 16 families, 154 genera, and 1,252 species of extant
scorpions.
A phylogenetic study by Soleglad and Fet (2003)
resulted in a widely debated revision of the higher classi-
fication of scorpions, which seemed to increase taxonomic
instability rather than improve it. This arrangement was
questioned by Prendini and Wheeler (2005), who chal-
lenged most of the changes made by Soleglad and Fet
(2003) and essentially returned scorpion taxonomy to its
pre-2003 state. The classification provided here follows that
of Prendini and Wheeler (2005), with modifications of the
included genera. For a listing of most of the valid genera,
see the Conspectus Genericus Scorpionorum of Dupré
(2007). The most recent estimate of scorpion taxonomic
diversity is 19 families, 213 genera, and 2,363 species
(modified from Rein, 2017, to follow Prendini and
Wheeler, 2005); it should be noted that in the past 20 years
more than 1,000 scorpion species have been described.
At least 106 species belonging to 21 genera and five
families are known to occur in the continental United
States; eight of these species are polytypic. A single species
(Paruroctonus boreus) occurs in the extreme southern
portions of British Columbia, Alberta, and Saskatchewan,
Canada. Mexico, with the highest scorpion diversity of any
country in the world, is home to 289 species spread among
37 genera and seven families.
The catalog by Fet et al. (2000), although now outdated,
remains an invaluable resource. The production of a new
catalog is in progress, with two parts already published
(Kova rík, 2009; Kova rík and Onjanguran Affilastro, 2013).
A partial key to the North American families is provided by
Ponce et al. (2016). Generic identifications of North
American scorpions are more problematic, as there is no
single reference that can be used; some sources that may be
Medical and Veterinary Entomology. https://doi.org/10.1016/B978-0-12-814043-7.00023-6
Copyright ©2019 Elsevier Inc. All rights reserved.
489

consulted include Soleglad and Fet (2006, 2008), Gonzalez
and Prendini (2013), and Ponce et al. (2016). For species
identification of the North American fauna, see the
following regional works: Nevada (Gertsch and Allred,
1965), Utah (Johnson and Allred, 1972), Idaho (Anderson,
1975), California (Hjelle, 1972; Williams, 1976); Baja
California, Mexico (Williams, 1980), Florida (Muma,
1967), and mainland Mexico (Ponce et al., 2016).
Buthidae
This is the largest and most widespread scorpion family,
with 90 currently recognized genera and more than 1,127
valid species. Buthids are found throughout the world with
their greatest diversity in the Old World, especially the
Afrotropical Region and the southern Palaearctic Region.
Most of the scorpions that are dangerously venomous
to humans and other animals belong to this family
(Table 23.1). The important genera in this respect are
Androctonus, Buthus, and Leiurus in northern Africa and
western Asia, Hottentotta in Asia and India, Parabuthus in
southern Africa, Centruroides in North America, and
Tityus in South America. Numerous other genera may
contain members of minor medical importance. Members
of this scorpion family are commonly encountered by
people and pets, making their status as venomous pests all
the more important. The only buthid genus that naturally
occurs in North America is Centruroides. Members of this
genus are crevice dwellers that commonly enter homes.
Five species occur in the United States. Centruroides
hentzi is found throughout Florida and adjoining portions
of Alabama and Georgia. Centruroides guanensis is
common on the islands of the Bahamas and Cuba but
is also found in the southernmost part of the Florida
Peninsula and the Florida Keys. Centruroides gracilis is
native to Central America and Mexico but has been
introduced to many other tropical areas including Florida.
Centruroides vittatus (Fig. 23.1) is the most widespread
species of scorpion in the United States, with a range that
extends from the Rio Grande River in the west to the
Mississippi River in the east. This species has been
collected as far north as southernmost Nebraska. It is
found throughout Texas and Oklahoma and in adjoining
parts of New Mexico, Colorado, Kansas, Illinois, Mis-
souri, Arkansas, and Louisiana. Centruroides sculpturatus
is found in most of Arizona, as well as adjoining parts
of New Mexico, Utah, Nevada, and California. All
species of Centruroides can deliver extremely painful
stings that can be accompanied by systemic symptoms.
However, only C. sculpturatus is considered dangerous,
but only to small children and the elderly. The only other
buthid occurring in the United States is the cosmotropical
species Isometrus maculatus, an Asian species that has
been introduced to tropical port cities around the world.
This species is common on the island of Oahu in Hawaii.
TABLE 23.1 Dangerous Species of Scorpions Based
on the Toxicity of Their Venoms
Species
Lethal
Dose (LD
50
)
Geographic
Occurrence
Leiurus
quinquestriatus
0.25 Turkey, Israel, Egypt,
Algeria, Libya, Sudan
Androctonus
mauretanicus
0.31 Morocco
Androctonus
australis
0.32 Morocco, Algeria,
Libya, Tunisia, Egypt
Androctonus
crassicauda
0.40 Turkey, Israel, Iraq,
Arabian Peninsula
Tityus
serrulatus
0.43 Brazil
Centruroides
limpidus
0.69 Mexico
Androctonus
amoreuxi
0.75 Middle East
Buthus
occitanus
0.90 Morocco, Algeria,
Jordan, southern
Europe
Centruroides
sculpuratus
1.12 United States, north-
ern Mexico
Parabuthus
transvaalicus
4.25 Southern Africa
The lethal dose is expressed as mg/kg of venom required to kill 50%
of mice (LD
50
) following subcutaneous injection. The lower the LD
50
,
the more potent is the venom. All of the scorpions listed are members
of the family Buthidae. (Compiled from multiple sources.)
FIGURE 23.1 Centruroides vittatus (Buthidae). A common scorpion in
the south central United States and northern Mexico. Photograph by W.
David Sissom.
490 Medical and Veterinary Entomology

Pseudochactidae
This recently described family contains one genus with two
species from Uzbeckistan, Tajikstan, and Afghanistan and
two genera with four species from Laos and Vietnam.
Members exhibit an unusual trichobothrial pattern similar
to that of the Buthidae.
Chaerilidae
This family is represented by the single genus, Chaerilus,
with 42 described species, none of which are dangerously
venomous. These scorpions are unique in many ways, but
they share some characteristics with the Buthidae. They
occur in the Old World in India, Sri Lanka, Nepal,
Bangladesh, Myanmar, Malaysia, Singapore, and many
islands of the Philippines and Indonesia.
Chactidae
This family contains 14 genera and approximately 199
species. None are known to be dangerous. Most of the
chactid species are found in South America (Colombia,
Venezuela, Trinidad and Tobago, Guyana, French Guiana,
Suriname, Ecuador, Peru, and Brazil). A few species are
found as far north as Panama and Costa Rica. One peculiar
species, Nullibrotheas alleni, is endemic to Baja California
Sur (Mexico). Anuroctonus, a genus of enigmatic phylo-
genetic position from California, Nevada, and Utah in
the United States and Baja California del Norte in Mexico,
is considered by some researchers to be a chactid.
Anuroctonus constructs permanent burrows in a variety of
habitats throughout its range and is associated with can-
yons, ravines, and hillsides.
Euscorpiidae
This small family shares many characteristics with the
Chactidae, of which it was once considered a subfamily.
Recent work on this family has resulted in a large number
of new species. Additionally, the members of the family
Scorpiopidae were transferred to this family (Soleglad
and Sissom, 2001), along with the genus Chactopsis, which
was formerly placed in the family Chactidae. There
are currently 12 genera and 137 species. One genus,
Euscorpius, with 59 species, is found throughout southern
(Mediterranean) Europe and has been variously divided
into four subgenera and numerous subspecies. Seven
genera of the former Scorpiopidae (now Scorpiopinae) may
be found at relatively high altitudes throughout their range.
They are native to parts of Afghanistan, Pakistan, India,
Sikkim, Nepal, China, Bangladesh, Myanmar, Thailand,
Laos, Vietnam, Malaysia, Indonesia, and Bhutan. None of
them are regarded as dangerous. Chactopsis is native to
South America (Peru, Venezuela, and Brazil). The other
genera in this family are found in eastern Mexico and
Guatemala. Megacormus and Plesiochactas are closely
related ground-dwelling (epigean) forms. The two species
of Troglocormus (Scorpiopinae) are troglobitic, having lost
the median eyes, and are found only in caves.
Superstitioniidae
This monotypic family was previously regarded as a
subfamily in the Chactidae. It shares few characters with
the Chactidae but instead is closely related to the Typhlo-
chactidae. Superstitioniidae contains the single species of
the genus Superstitionia.Superstitionia donensis is found
throughout much of the southwestern United States,
including Arizona, Nevada, California, and southwestern
New Mexico, as well as adjacent parts of northern Mexico.
It is a small, uncommon scorpion and is not known to be
medically important.
Typhlochactidae
The Typhlochactidae includes four genera and 11 species
known mostly from caves in Mexico; two species are
associated with leaf-litter habitats. All species lack both
median and lateral eyes and have reduced or no pigmen-
tation; some have attenuated appendages. They are gener-
ally small in size. At 9 mm total length, Typhlochactas
mitchelli is one of the smallest species of scorpion in the
world. The one exception in the family is Alacran tartarus,
which measures up to 70 mm in length.
Troglotayosicidae
The two genera in this family were formerly placed in
the Superstitioniidae. Both are poorly known, and their
relationships remain uncertain. These species burrow
underground (endogean) or live just beneath the ground
surface (hypogean), and they possess lateral eyes but no
median eyes. The four species of Troglotayosicus are
known from Ecuador and Colombia. Belisarius xambeui,
from caves in the eastern Pyrenees of Spain and
France, was traditionally grouped with Euscorpius, with
which it bears a superficial resemblance; however, this
species, and a second one recently described from southern
Spain, share a number of significant features with
Troglotayosicus.
Akravidae
This family is based on a single troglobitic species
described in 2007. The family is of dubious validity, and
Scorpions (Scorpiones) Chapter | 23 491

phenetic comparisons place it near the Superstitioniidae and
Typhlochactidae (Soleglad and Fet, 2011).
Iuridae
This interesting but small group of scorpions is restricted to
south central Eurasia. None of them are considered
dangerous. There are four genera and approximately 14
species. The genera Iurus,Calchas,Neocalchas, and
Protoiurus are closely related, relatively large, and found in
Turkey, Greece (including Samos, Crete, and other
islands), Iraq, and possibly Syria.
Caraboctonidae
The Caraboctonidae is a New World family with four
genera and 32 species. The genera Caraboctonus (one
species) and Hadruroides (22 species) are found in western
South America. Caraboctonus is found in Chile and Peru;
Hadruroides is distributed through Ecuador (including
the Galapagos Islands), Bolivia, Peru, and Chile. There
are seven species in the genus Hadrurus that occur in
desert areas of Oregon, Idaho, California, Nevada,
Utah, Colorado, and Arizona (USA), as well as
Sonora, Baja California Norte, and Baja California Sur
(Mexico). Additionally, two species from south central
Mexico formally contained in Hadrurus were recently
placed in their own genus, Hoffmannihadrurus (Fet et al.,
2004).
Vaejovidae
This family is composed of 26 described genera and
approximately 214 species that are restricted mostly to
North America. Species of Vaejovidae are found in
every conceivable habitat in nearly every state of Mexico
and much of the United States, especially the west
(Washington, Oregon, Idaho, Montana, Wyoming, Cali-
fornia, Nevada, Utah, Colorado, North Dakota, South
Dakota, Nebraska, Arizona, New Mexico, and Texas).
One species ranges south into Guatemala, while another
species can be found in Canada. Vaejovis carolinianus
occurs in wooded, mountainous areas of the eastern
United States (parts of Kentucky, Tennessee, Virginia,
North Carolina, South Carolina, Georgia, Alabama, Mis-
sissippi, and Louisiana). It is a small (about 2.4 cm), dark
scorpion that readily enters homes throughout its range.
Other species also may occur indoors, such as members of
the genera Pseudouroctonus and Uroctonus that
commonly enter homes in California. No members of this
family pose any appreciable health threat, but stings from
these species are more likely to cause minor localized
discoloration, swelling, and necrosis than are the more
painful stings of buthid scorpions.
Bothriuridae
This family of 17 genera and 154 species exhibits a
Gondwanan distribution. One genus, Cercophonius, with
seven described species, is distributed throughout Australia
but is also found on New Caledonia and in northern India;
the latter species is considered by most researchers to be of
dubious validity. Two genera, Lisposoma, with two spe-
cies, and Brandbergia, with one species, are endemic to
Namibia. The remaining genera are distributed throughout
western and southern South America (Ecuador, Peru,
Brazil, Bolivia, Paraguay, Chile, Argentina, Uruguay).
None of the bothriurids are considered medically important.
Hormuridae
Formerly known as Ischnuridae and Liochelidae, or
considered a subfamily of the Scorpionidae, the hormurids
are now regarded as a separate family. They range in size
from small to very large and typically have a flattened body
shape. The claws are massive in comparison to the body,
but the metasoma is unusually thin and feeble-looking.
Sometimes the metasoma is so short that it cannot reach to
the front of the animal. Though capable of burrowing, most
of these species are associated with crevice habitats in
rocky areas, on trees, under debris, on man-made structures
such as stone walls and wooden bridges, etc. The most
impressive of the family is Hadogenes troglodytes from
South Africa, the males of which can attain a body length
up to 21 cm.
The family contains 11 genera and 88 species. Repre-
sentatives are widely distributed throughout the tropics. In
the Caribbean they are found in Haiti and Dominican Re-
public; in Central America: Panama and Cocos Island
(Costa Rica); in South America: Peru, Colombia,
Venezuela, French Guiana, Brazil; in central and southern
Africa: Cameroon, Democratic Republic of Congo, Gabon,
Congo, Malawi, Uganda, Ethiopia, Kenya, Tanzania,
Angola, Namibia, Botswana, Zimbabwe, Mozambique,
South Africa, Lesotho, Swaziland, Mauritius, Round Is-
land, Seychelles, Zanzibar, Madagascar; in Asia: China,
Korea, Japan, India, Aru Islands, Bangladesh, Myanmar,
Thailand, Cambodia, Laos, Vietnam, Malaysia, Indonesia,
Philippines, Papua New Guinea; in Oceania: Federated
States of Micronesia, Fiji, French Polynesia, Key Islands,
Kiribati, Mariana Islands, Marshal Islands, New Caledonia,
Palau, Ponape, Tuvalu, Samoa, Solomon Islands, Tonga,
Vanuatu; and, of course, Australia. As a group, they are
considered relatively harmless. In the case of stings by
the giant Hadogenes scorpions, the effect may be so slight
as to be barely felt. Other species, such as Opisthacanthus
lepturus in Panama, can deliver a sting that causes soreness
in joints, as well as mild, localized discoloration, swelling,
and necrosis.
492 Medical and Veterinary Entomology

Heteroscorpionidae
This is a tiny family with one genus (Heteroscorpion) and
six species that are endemic to Madagascar. This genus was
formerly placed among the Ischnuridae, with which they
share many characteristics. Their medical importance is not
known.
Hemiscorpiidae
Members of this family superficially resemble members of
the Hormuridae, being flattened and possessing a thin,
delicate postabdomen. They are crevice dwellers like many
of the hormurids. In the past, they have been variously
placed in the Hormuridae or the Scorpionidae. There is a
total of 16 species in this group. All are considered to
belong to a single genus, Hemiscorpius, although some
authors still recognize the validity of the monotypic genus
Habibiella. These species are found in Somalia, Eritrea,
Saudi Arabia, Yemen, Oman, United Arab Emirates, Iraq,
Iran, and Pakistan. Hemiscorpius lepturus in Iran is the
only nonbuthid species of scorpion reported to cause sig-
nificant mortality in humans. The venom contains a potent
cytotoxin that causes severe tissue damage and necrosis
near the sting site, as well as severe systemic symptoms.
The medical importance of the other species of Hemi-
scorpius is not known; however, it is safe to assume that
they have venom that, at the very least, causes soreness in
joints, as well as mild, localized discoloration, swelling,
and necrosis, as in their close relatives, the Hormuridae and
Scorpionidae.
Urodacidae
This family, often considered a subfamily of Scorpionidae,
contains two genera, Urodacus and Aops, which are
endemic to Australia. There are 21 described species of
Urodacus and a single species of Aops.Aops oncodactylus
is troglobitic. None are known to be dangerous.
Diplocentridae
This is another comparatively small family with 10 genera
and 130 described species that occur primarily in the New
World. Exceptions are the genera Nebo, found in Syria,
Jordan, Lebanon, Israel, Egypt (Sinai), Saudi Arabia,
Yemen, and Oman, and two species of Heteronebo,both
known from the island of Abd-el-Kuri (Yemen). Oddly, the
other 17 species of Heteronebo are found on various islands
in the Caribbean, along with the genera Oiclus,Cazierius,
Cryptoiclus, and most of the species in the genus Didymo-
centrus. The latter genus is also represented in Honduras,
El Salvador, Nicaragua, and Costa Rica. Another genus,
Tarsoporosus, is found in Venezuela and Colombia. The
genus Bioculus is endemic to Baja California Sur (Mexico)
and its associated islands. Widespread through Honduras,
Guatemala, Belize, and Mexico, Diplocentrus,with64
described species, is the largest genus in the family
(Fig. 23.2). Five species occur in the southern parts of
Arizona, New Mexico, and Texas (USA). Two species of
Kolotl occur in southern Mexico. Diplocentrids are not
generally considered dangerous. However, stings from the
Middle Eastern species Nebo hierichonticus may cause mild,
local hemorrhages and slight necrosis.
Scorpionidae
As the oldest recognized scorpion family, this group once
included all known scorpions. Over the years, its scope
has been reduced. Currently, the family is compact and
homogeneous, with nine genera and 157 species, and
includes some of the world’s largest and most formidable-
looking scorpions. All are heavy-bodied with large,
powerful pedipalps. Some members of the Asian genus
Heterometrus reach lengths of 16 cm or more. Pandinus
imperator from West Africa is often cited as one of the
largest scorpions, occasionally attaining a body length of
18 cm and weighing up to 32 g as nongravid females
(Fig. 23.3). This large, black scorpion is commonly sold in
pet stores. The 17 species of Scorpio are distributed across
northern Africa (Senegal, Mauritania, Morocco, Algeria,
Tunisia, Libya, Egypt) and the Middle East (Turkey,
Lebanon, Syria, Iraq, Kuwait, Iran, Israel, Jordan, Saudi
Arabia, Qatar, Yemen). The former genus Pandinus,
containing the large African emperor scorpions, is now
subdivided into four genera: Pandinus, Pandinurus,
FIGURE 23.2 Diplocentrus diablo (Diplocentridae). Lower Rio Grande
Valley in Texas (USA) and adjacent Mexico. Photograph by W. David
Sissom.
Scorpions (Scorpiones) Chapter | 23 493