Schizocosa stridulans
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''Schizocosa stridulans'' is a sibling species of '' S. ocreata'' and ''S. rovneri'' and is part of the wolf spider family. The name of the genus comes from the epigynum structure (external female genitalia) being
lycosid Wolf spiders are members of the family Lycosidae (). They are robust and agile hunters with excellent eyesight. They live mostly in solitude, hunt alone, and do not spin webs. Some are opportunistic hunters, pouncing upon prey as they find it or ...
and having a split T excavation. This spider is well-known for its specific leg ornamentation and courtship rituals and that is how it has been differentiated from its related species. The ''S. stridulans'' take systematic steps during its courtship ritual, which involves two independent signals. More specifically, female spiders will leave silk and pheromones to communicate that they are ready to mate.


Physical and anatomical characteristics


Appearance

These are medium to large wolf spiders with strong legs and a sharp vision. Their body size ranges from less than 10 mm to about 35 mm. Wolf spiders have eight eyes present in 3 rows, with 4 small eyes in the bottom row, 2 large eyes in the middle, and 2 medium-sized eyes at the top. The '' Schizocosa'' genus is known for striking light and dark bands seen on the spider’s carapace (upper section of the exoskeleton) and abdomen. It was initially thought that this species was a hybrid of the ''S. ocreata'' and the ''S. rovneri'', however studies conducted to compare behaviors of hybrids and ''S. stridulans'' emphasized that they are indeed separate species. ''S. stridulans'' males lack the bristles on the first leg pair when matured, however there are regions of dark pigmentation on the
tibia The tibia (; ), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outside of the tibia); it connects ...
,
patella The patella, also known as the kneecap, is a flat, rounded triangular bone which articulates with the femur (thigh bone) and covers and protects the anterior articular surface of the knee joint. The patella is found in many tetrapods, such as ...
, and distal area of the
femur The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates wit ...
. This species is also smaller in size compared to the sisters ''S. ocreata'' and ''S. rovneri''. There are only minor differences in the appearances of the male and female, so there does not seem to be pronounced sexual dimorphism. The ornamental marking on the forelegs are important for courtship. Males have a brown carapace with a pale middle band and yellow brown
sternum The sternum or breastbone is a long flat bone located in the central part of the chest. It connects to the ribs via cartilage and forms the front of the rib cage, thus helping to protect the heart, lungs, and major blood vessels from injury. Sha ...
; the margins are smooth and there is a narrowing in the posterior third region of the carapace. The brown
chelicerae The chelicerae () are the mouthparts of the subphylum Chelicerata, an arthropod group that includes arachnids, horseshoe crabs, and sea spiders. Commonly referred to as " jaws", chelicerae may be shaped as either articulated fangs, or similarl ...
appendages ar
setaceous
and they consist of three uneven teeth on the promargin and three even teeth on the retromargin of the fang furrow. The legs are usually yellow with dark streaks on the femur and tibia, and leg I commonly has black pigmentation of the
tibia The tibia (; ), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outside of the tibia); it connects ...
and
patella The patella, also known as the kneecap, is a flat, rounded triangular bone which articulates with the femur (thigh bone) and covers and protects the anterior articular surface of the knee joint. The patella is found in many tetrapods, such as ...
, also known as
“five-o-clock shadow”
On the tibia, there are short black hairs present and the abdomen has a heart mark in most specimens. There is a median apophysis which is undulating and convex, and a thickened margin terminal apophysis. Females have comparable coloration to the males of these species, the appearance of the sexes differing mainly in bands and excavations. The
chelicerae The chelicerae () are the mouthparts of the subphylum Chelicerata, an arthropod group that includes arachnids, horseshoe crabs, and sea spiders. Commonly referred to as " jaws", chelicerae may be shaped as either articulated fangs, or similarl ...
(mouthparts) match those observed in the males. On the
prosoma The cephalothorax, also called prosoma in some groups, is a tagma of various arthropods, comprising the head and the thorax fused together, as distinct from the abdomen behind. (The terms ''prosoma'' and ''opisthosoma'' are equivalent to ''cepha ...
(cephalothorax), they display a pale median band behind the eyes. The transverse piece has marked paired excavations which meet at the midline and these excavation distances vary from nearly no space to about the width of one excavation.


Speciation

''Schizocosa stridulans'' and their sister species ''S. ocreata'' and ''S. rovneri'' are thought to be ethospecies that are distinctive in behavior but not easily distinguished morphologically. Since these sympatric pairs differ in courtship behaviors, they were provided with the status of being separate species from the results of interbreeding studies. Their speciation is thought to have originated due to allochrony.


Distribution


Habitat

This species shares the geographic distribution of its sister species ''S. rovneri'' and ''S. ocreata''. Their general habitat is humid, moist areas in leaf litters, usually in oak or oak hickory forests. There is sometimes co-occurrence of ''S. stridulans'' with its sister species, otherwise most of the time the populations are found alone. It is usually courting behavior that allows for clear distinction between ''S. stridulans'' and ''S. ocreata'' and ''S. rovneri'' when the populations intermingle.


Burrows

Wolf spiders do not spin webs, rather they create burrows in which they live. In order to move in and out of the burrows, silken doors are developed at the entrance to the burrows. During heavy rains, these spiders uses pebbles, turrets, and twigs to prevent flood water from entering their well built burrows. The distribution of ''S. stridulans'' in their range depends on the type of habitat and the level of disturbance. The intraspecific densities vary to some extent between post oak woodlands and disturbed habitats, however ''S. stridulans'' is less affected by these discrepancies compared to its sister species ''S. rovneri'' and ''S. ocreata''.


Range

The genus ''Schizocosa'' has been spotted in most continents including North America, South America, Asia, and Africa. ''S. stridulans'' have been found in southeast and midwest US, specifically in the states of Missouri, Ohio, Kentucky, Tennessee, Mississippi, and Alabama.


Diet

Spiderlings and adults generally share the same diet. Based on the type of prey available, their foraging behavior is adapted accordingly and most spiders have diverse diets and consume a variety of prey types. Some of the common prey are ''
Collembola Springtails (Collembola) form the largest of the three lineages of modern hexapods that are no longer considered insects (the other two are the Protura and Diplura). Although the three orders are sometimes grouped together in a class called Ento ...
'', '' Diptera'', and ''Ensifer''. ''S. stridulans'' has to balance its time and energy to forage based on availability of prey and predation frequency. Even during
overwintering Overwintering is the process by which some organisms pass through or wait out the winter season, or pass through that period of the year when "winter" conditions (cold or sub-zero temperatures, ice, snow, limited food supplies) make normal activi ...
for both juveniles and adults, there is regular feeding. Something interesting about ''S. stridulans'' is that they consume the more abundant dietary resource at a lower rate and they focus more energy on foraging the less abundant prey.


Hunting behavior

Wolf spiders typically are solitary dwellers and hunt for prey alone as well, usually not aggressively. At times, they are opportunistic in hunting and pounce on their desired prey, and they may even chase their prey depending on availability. It is also common for spiders to wait for prey to pass near the entrance of their burrow and then lure them in to eat them. High availability of prey reduces cannibalism rates, otherwise a hungry female will end up eating her male. This gives the female a dietary resource during times of less abundant prey, and also prevents that male of fertilizing other females’ eggs.


Reproductive behaviors


Courtship and mating success

The male courtship behavior of ''S. stridulans'' varies a lot from ''S. ocreata'' and ''S. roverni''. ''S. stridulans'' males have a courtship ritual involving movements of the palp and first leg pair. This begins when mature females leave silk and pheromones to indicate to the mature males in the area and they are ready to mate. The two components of this ritual are revs and idles which are independent signals; the revs involve flexing the pedipalp and trembling of the abdomen, while the idles are percussive foreleg tapping sounds. Most of the time, the male spiders tend to alternate between
stridulation Stridulation is the act of producing sound by rubbing together certain body parts. This behavior is mostly associated with insects, but other animals are known to do this as well, such as a number of species of fish, snakes and spiders. The mech ...
(make noise by rubbing body parts together) and audibly tapping the forelegs. In the courtship display, the seismic courtship signal, which is based on the surrounding environment, is seen to prevail over the visual aspect in order for mating success. Visual signals have a significantly greater importance in the absence of a seismic signal, and this was concluded from experiments using video playbacks of the courtship signals. When there is visual signaling, the detectability of a male is significantly increased, and females are naturally more attracted to ornate displays along with the seismic signals. Another factor observed to be affecting female choice is diet, and it was shown that high diet females usually mated more with high diet males, whereas low diet females did not differentiate much. In addition, one unique behavior of ''S. stridulans'' is that whenever courtship rates become especially high, females actively choose to mate with less ornate males because it is correlated to less aggression from the males. Females are more picky when there are high numbers of males available and missing out on copulations is not an issue. The attractive males have a strong advantage when courtship rates are low since they can quickly impress and mate with the female. The tap frequency and the volume of the pulses increases as mounting and copulation is about to happen. In some cases after mating, the female kills and eats her mate, otherwise the males survive to mate with other available females. Males of this species do not try to attract ''S. ocreata'' or ''S. rovneri'' females and likewise, females do not allow for courting from males from the sister species.


Reproduction

The courtship period can range from 3 minutes and 45 seconds to over 43 minutes, as observed in studies. In order to demonstrate receptivity to the male, the female lowers her
prosoma The cephalothorax, also called prosoma in some groups, is a tagma of various arthropods, comprising the head and the thorax fused together, as distinct from the abdomen behind. (The terms ''prosoma'' and ''opisthosoma'' are equivalent to ''cepha ...
(head and thorax), rotates at least 90 degrees, and shakes her forelegs, walking away from and then back toward the male. In the copulation, the male inserts in his palp several times on one side and then continues inserting on the opposite side. The stridulation sounds of ''S. stridulans'' can be qualitatively distinguished from the bounces of ''S. rovneri'' and active jerky pulses of the ''S. ocreata''. For ''S. stridulans'', ''S. ocreata'', and ''S. rovneri'', the female behavior shares the common components of pivot, turn, and settle.


Parental care

There is generally little parental care in these wolf spiders because their lifespan is of about 1 year, and parents tend to die within 1–2 months of their offsprings’ birth. These wolf spiders lay their 100 or so eggs in a safe and isolated location. During the short parental care time, female spiders carry around their spherical egg sacs on their
spinneret A spinneret is a silk-spinning organ of a spider or the larva of an insect. Some adult insects also have spinnerets, such as those borne on the forelegs of Embioptera. Spinnerets are usually on the underside of a spider's opisthosoma, and a ...
s (organs that produce silk) so they protect them as much as possible. They prevent the egg sac from touching the ground while they move around to hunt by maintaining a raised position of their abdomen. At hatching time, the females rip open their egg sacs and the spiderlings swarm over the female’s body, specifically at the dorsal abdomen. After the spiderlings emerge from the eggs, they stay with their mother only for a few weeks, then they move on to live independently from their parents. '' Schizocosa'' and other wolf spiders do not carry spiderlings on their back at any point.“Wolf Spider Life Cycle - Eggs, Babies & Adults.” Orkin.com, www.orkin.com/other/spiders/wolf-spiders/life-cycle.


Interspecies interactions


Enemies

The main predators of wolf spiders are wasps, amphibians, small reptiles, shrews, coyotes, and some spider-eating birds. Several wasp species utilize wolf spiders as a means to incubate their eggs. Wasp mothers paralyze spiders with their stingers for some time and inject their eggs inside and once the larvae develop inside, they consume the spider inside-out. Shrews require constant dietary intake so even though wolf spiders are small meals, they are known to consume many such small spiders just like coyotes. In addition, wolf spiders are susceptible when they venture out alone to hunt, and can be attacked by birds during that time.


Protective coloration and defense

They depend on camouflage for protection from predators, so their coloration is meant to match the leaf litter in their habitat. This is why the body coloration is dull and there is little flashy ornamentation to unnecessarily attract attention toward itself. ''S. stridulans'' is known for its agility and this helps them in escaping from predators. If they are attacked aggressively by predators or other competitors, then wolf spiders typically use their strong large jaws to bite. In a life or death situation, a wolf spider might let its leg get bitten off for survival at the moment, though it reduces their quickness and makes them susceptible to attack later on.


Physiology

Wolf spiders are known for their large eyes which give them an advantage with their keen vision. They also have an abundance of sensitive sensory hairs all over the legs and bodies, adding to their strong sense of touch. Another special aspect of wolf spiders is their grate shaped tapetum lucidum, a reflective tissue present in their four secondary eyes, giving them a visible glow.


Thermoregulation


Overwintering

''Schizocosa stridulans'' are rather active in the winter and are seen gaining a considerable amount of weight throughout those months. In the studies conducted by Potts, the spiders had less fluctuating protein levels, however their lipid and carbohydrate counts decreased throughout the winter. During that time, ''S. stridulans'' accumulated glycerol and a few other previously known
cryoprotectant A cryoprotectant is a substance used to protect biological tissue from freezing damage (i.e. that due to ice formation). Arctic and Antarctic insects, fish and amphibians create cryoprotectants ( antifreeze compounds and antifreeze proteins) in ...
s. The spiders are more active on the warmer winter days, and are relatively vulnerable in extremely cold conditions.


Bites

''Schizocosa stridulans'' rarely bite and if they do, it is the result of consistent provocation. Other wolf spiders are known to inject venom, however they cause only mild symptoms such as swelling, rashes, and itching. Certain cases of
necrotic Necrosis () is a form of cell injury which results in the premature death of cells in living tissue by autolysis. Necrosis is caused by factors external to the cell or tissue, such as infection, or trauma which result in the unregulated dige ...
bites, those that result in dead tissue, have been seen by South American and Australian spiders but this is infrequent.


Interactions with humans and livestock

Wolf spiders eat a variety of small nuisance insects, and therefore they are essential to the naturally present population control of their prey and are beneficial to farmers and gardeners.


References

{{Taxonbar, from=Q2254293 Lycosidae