General Household Pests: Scorpions

Contents


Introduction

Scorpions have long been of interest to humans primarily
because of their ability to give painful and sometimes
life threatening stings. Scorpions are also an
important and beneficial component of many ecosystems
and they are one of the oldest known terrestrial
arthropods. Fossil scorpions found in Paleozoic strata
430 million years old appear very similar to present
day species.

Scorpions are venomous arthropods in the class
Arachnida, relatives of spiders, mites, ticks, solpugids,
pseudoscorpions and others. There are currently 1400
recognized species of scorpions worldwide. Scorpions
have an elongated body and a segmented tail that
is tipped with a venomous stinger. They have four
pairs of legs and pedipalps with plier-like pincers on
the end, which are used for grasping.

Range and Habitat

Scorpions are commonly thought of as desert animals,
but in fact, they occur in many other habitats,
including grasslands and savannahs, deciduous forests,
montane pine forests, intertidal zones, rain forest
and caves. Scorpions have even been found under
snow-covered rocks at elevations of over 12,000 feet in
the Himalayas of Asia.

Description

As arachnids, scorpions have mouthparts called chelicerae,
a pair of pedipalps, and four pairs of legs. The
pincer-like pedipalps are used primarily for prey capture
and defense, but are also covered with various
types of sensory hairs. The body is divided into two
main regions, a cephalothorax and an abdomen.

The cephalothorax is covered above by a carapace (or head
shield) that usually bears a pair of median eyes and 2
to 5 pairs of lateral eyes at its front corners (a few cave
and litter-dwelling scorpions are completely eyeless).
The abdomen consists of 12 distinct segments, with
the last five forming the metasoma what most people
refer to as the “tail”. At the end of the abdomen is the
telson, which is a bulb-shaped structure containing
the venom glands and a sharp, curved stinger to deliver
venom.

On its underside, the scorpion bears a pair of unique
comb-like sense organs called the pectines; these are
usually larger and bear more teeth in the male and are
used to sense the texture and vibration of surfaces. They
also serve as chemoreceptors (chemical sensors) to detect
pheromones (communication chemicals).

The “long-tailed” African Scorpion (Hadogenes troglodytes)
reaches a length of over 8 inches, and is probably
the longest scorpion in the world. Some of the
African and Asian Emperor Scorpions routinely reach
(and probably exceed) 7 inches. The largest scorpions
in the United States are members of the genus Hadrurus
(giant desert hairy scorpions), obtaining a length of
about 5 inches.

Desert hairy scorpion

Desert hairy scorpion



Behavior

Scorpions are nocturnal or diurnal, predatory animals
that feed on a variety of insects, spiders, centipedes,
and other scorpions. The larger scorpions occasionally
feed on vertebrates, such as small lizards,
snakes, and mice. Prey is detected primarily by sensing
vibrations with the pectine organs. The pedipalps
have an array of fine sensory hairs that sense air-borne
vibrations; the tips of the legs have small organs that
detect vibrations in the ground. Most scorpions are
ambush predators who detect prey when it comes
within reach.

The surfaces of the legs, pedipalps, and body are
also covered with thicker hairs (setae) that are sensitive
to direct touch. Although they are equipped with
venom for defense and prey acquisition, scorpions
themselves fall prey to many types of creatures, such
as centipedes, tarantulas, lizards, snakes,
birds (especially owls), and mammals (including
shrews, grasshopper mice, and bats).

As with many predators, scorpions tend to forage in
distinct and separate territories, returning to the same
area each night. They may enter homes and buildings
when their territory has been disrupted by construction,
tree removal or floods, etc.
Scorpions have many adaptations for desert living.
They have extra layers of lipids (fats) on their exoskeleton
(external skeleton) that minimizes water loss. Most
are active at night, and spend their days where it is
cool and moist under rocks, wood, tree bark or in burrows.
Although scorpions have been seen drinking
directly from water reservoirs, they derive most of their
water from their food (although this varies by species).
As with most arthropods their activity is linked to
temperature. Generally speaking, scorpions are active
if nighttime temperatures are above 70oF. They tend to
be less active during winter and the hottest part of the
summer during daylight hours.

Life Cycle

Scorpions have a complex mating ritual in which
the male uses his pedipalps to grasp the female’s pedipalps.
The male then leads her in a “courtship dance”.
The details of courtship vary from species to species,
with some even exhibiting a deliberate and prolonged
“sexual sting” by the male. The sperm from the male is
contained within a structure called a spermatophore,
which is deposited by the male on a surface over which
the female is pulled. The male sweeps his pectines
over the ground surface to help locate a suitable place
to deposit his spermatophore. The female draws the
sperm into her genital pore, which is located near the
front ventral (under) side of her abdomen.

Female bark scorpion with young on her back

Female bark scorpion with young on her back

Scorpions have a long gestation period (from several
months to over a year, depending on species) in which
the young develop as embryos in the female ovariuterus
or in specialized diverticula that branch from the
ovariuterus. The young are born live and climb to their
mother’s back. She assists them by making a “birth
basket” with her folded legs to catch them as they are
born and to provide them with a means to climb to her
back. A few Old World species do not form birth baskets.

On average, a female gives birth to about 25-35 young.
They remain on her back until they molt for the first
time. The white colored young have been seen to climb
down off the mothers back, molt then return to the mothers
back for another 4-5 days before leaving for good,
usually within one to three weeks after birth. Once
they climb down, they assume an independent existence,
and periodically molt to reach adulthood. Typically
five or six molts over two to six years are required
for the scorpion to reach maturity.
The average scorpion probably lives three to five
years, but some species may live up to 25 years. A few
scorpions exhibit social behaviors beyond the mother young
association, such as forming over-wintering aggregations,
colonial burrowing, and perhaps even living
in extended family groups that share burrows and
food.

Scorpion Venom

The venom of scorpions is used for both prey capture,
defense and possibly to subdue mates. All scorpions
do possess venom and can sting, but their natural
tendencies are to hide and escape. Scorpions can control
the venom flow, so some sting incidents are
venomless. Scorpion venoms are complex mixtures of neurotoxins (toxins which
affect the victim’s nervous system) and other substances;
each species has a unique mixture.

Despite their bad reputation, only one species in the western
U.S. (the bark scorpion, Centruroides exilicauda) and
about 25 others worldwide have venom potent enough
to be considered dangerous to humans.
The world’s most dangerous scorpions live in North
Africa and the Middle East (species in the genera
Androctonus, Buthus, Hottentotta, Leiurus), South America
(Tityus), India (Mesobuthus), and Mexico (Centruroides).
In some of these areas, scorpion stings may be a significant
cause of death, but reliable data on human
mortality are not readily available. Some studies suggest
typical mortality rates up to about 4% in hospital
cases, with children and the elderly being most susceptible.
Death by scorpion sting, if it occurs, is the
result of heart or respiratory failure some hours after
the incident. During the 1980’s Mexico averaged about
800 deaths each year. In the past 20 years
there have been no reported fatalities in the United States due to
scorpion stings.

Management of Scorpions

High numbers of scorpions can become a problem
under some circumstances. If a reduced population is
desirable several steps can be taken.
Scorpions are difficult to control with insecticides
alone. Therefore, the first control strategy is to modify the area surrounding a house or structure:

  • Remove all harborages such as: trash, logs, boards, stones, bricks and other objects from around the building
  • Keep grass closely mowed near the home
  • Prune bushes and overhanging tree branches away from the structure
  • Tree branches can provide a path to the roof for scorpions
  • Minimize low growing ground cover vegetation
  • Store garbage containers in a frame that allows them to rest above ground level
  • Never bring firewood inside the building unless it is placed directly on the fire
  • Install weather-stripping around loose fitting doors and windows
  • Plug weep holes in brick veneer with steel wool, pieces of nylon scouring pad or small squares of screen wire
  • Caulk around roof eaves, pipes and any other cracks into the building
  • Keep window screens in good repair, make sure they fit tightly in the window frame
  • By managing the scorpion food source, you can manage the scorpion population

Blacklighting

Bark scorpion viewed under U.V. light

Bark scorpion viewed under U.V. light

Scorpions fluoresce or glow under ultra-violate light
so they are easy to find in some areas with high populations with the aid of a black light during the night. Nighttime scorpion hunting is a lot
of fun but make sure that you wear high-top boots and
have long tongs if you want to capture the scorpions to
move them.

Be sure scorpion populations are high in your area before you go through the expense of constructing one of the following light systems. Many states do not have population densities that would make this activity enjoyable!

Using black light bulbs you can construct your own portable
U.V. light. Homeowners wishing to construct an
inexpensive black light should purchase a 6-volt camping
lantern with a 6-inch fluorescent tube, from a camping
supply store or department store. The tube can
then be replaced with an ultraviolet bulb available at
many lighting stores. This kind of light will show scorpions
1-2 feet from the light.

Bark scorpion viewed under normal daylight

Bark scorpion viewed under normal daylight

The approximate cost of constructing the 6 volt blacklight will be $30. Another option is to obtain a 12 volt fluorescent fixture, such as
an emergency auto lighting stick and a 12 volt rechargeable
battery pack available at electronics supply stores.
Replace the bulb with a 12 volt, 8 watt ultraviolet bulb
from a lighting store. This is a more powerful system
and will cost more to construct, but will allow nighttime
viewing of scorpions from 4-5 feet away. The approximate
cost of constructing the 12 volt blacklight will be $200.

Once located, collect the scorpions using long forceps
or tongs and keep them in a sealable, sturdy container.
As these wonderful creatures are such a benefit
to our environment please consider collecting and releasing
the scorpions into the area they were collected rather than
killing them. If collected scorpions are to be destroyed,
crush the individuals then use a flyswatter or long forceps
to remove the bodies. Chemical spraying during
the day is largely ineffectual.

Scorpion-like Creatures

Besides true scorpions, there are a number of other
arachnids that look similar and at first glance may be
confused with scorpions.

Pseudoscorpion

Pseudoscorpion

Pseudoscorpions are arachnids with a body length
of approximately 1/8th inch. The pedipalps give them
a strong resemblance to true scorpions. Natural habitats
for pseudoscorpions include under leaf litter and
mulch, in moss, under stones and beneath tree bark.
They have also been reported in bird nests and between
siding boards of buildings. Pseudoscorpions are predaceous
and can inflict a venomous bite.

Solpugids

Solpugids

Solpugids are pale-tan arachnids. The body can be
up to an inch and a half in length, with a pair of heavy
pinchers dominating the front end. They have four
pairs of long legs and pedipalps in front that are used
in touching and smelling. They run fast and climb
well. Solpugids subdue their prey with their pinchers,
which lack poison glands.

Whipscorpions

Whipscorpions

Whipscorpions are found in the southeastern oak
zone of Arizona eastwards across the southern U.S. to
Florida. They have a substantial but flat body 2-3
inches in length, with large spined, arm-like pedipalps
in front. They are arachnids but have no venom.
Whipscorpions are predators, active at night. The
whip-like tail is used in defense and individuals can
squirt acetic acid (vinegar) produced from a rear gland.

Tailless whipscorpions

Tailless whipscorpions

The front of this animal is similar to the
whipscorpion, with heavily spined, grasping arms.
They also have a pair of very long and limber front
legs, which are used to touch and smell. Tailless
whipscorpions are dark brown in color and the width
across it’s very flattened body can exceed an inch. They
are predators and have no venom. As their name implies
they lack a tail.

Pseudoscorpions, solpugids, whipscorpions and
tailless whipscorpions do not sting like scorpions, control
is unnecessary and they provide excellent control
of cockroaches. Do not intentionally handle them as
they are delicate creatures.

Tips for Professionals

  • Wettable powder formulations provide better residual control for crawling pests when applying perimeter sprays.
  • Daytime spraying is largely ineffective. In areas with large populations the most effective scorpion management method is nighttime blacklight collecting.
  • When using insecticides labeled for scorpion control, be sure to use the highest permissible label rate.
  • Apply pesticides around the foundation of the building and up to 1 foot above ground level on the exterior walls. Also apply pesticides around doors, window eaves and other potential points of entry.
  • Always follow label directions on the package for dosage, mixing and application methods.

Authors of this publication: Dawn Gouge, Kirk Smith, Carl Olson and Paul Baker of the University of Arizona.