Spider cannibalism is the act of a spider consuming all or part of another individual of the same species as food. It is most commonly seen as an example of female sexual cannibalism where a female spider kills and eats a male before, during, or after copulation. Cases of non-sexual cannibalism or male cannibalism of females both occur but are notably rare.
Many cultures, such as South Africa and Slovakia, [1] believe that the male (usually significantly smaller than the female, down to 1% of her size as seen in Tidarren sisyphoides ) is likely to be killed by the female after the coupling, or sometimes even before intercourse has been initiated. This supposed propensity is what gave the black widow spider, Latrodectus mactans, its name. However, the three species of North American black widows do not usually kill the male (although they have been known to do so). Males can sometimes even live in the web of a female for a period without being harmed in any way. The male Australian redback spider Latrodectus hasselti is killed by the female after he inserts his second palpus in the female genital opening; in over 60% of cases the female then eats the male.
Although the male Latrodectus hasselti may sometimes die during mating without the female actually consuming him, this species represents a possible strategy of "male sacrifice". The male redback, while copulating, "somersaults" and twists his abdomen directly onto the fangs of his mate. Approximately 65% of males are consumed at this stage. [2] Males that "sacrifice" themselves gain the benefit of increasing their paternity relative to males who do not get cannibalized. [2]
Despite these examples and many other similar reports, however, the theory of the "sacrificial male" has become greater than the truth. Mating of spiders is not always followed by cannibalism. Indeed, scholars have noted that the "supposed aggressiveness of the female spider towards the male is largely a myth" and that cannibalism only occurs in exceptional cases. [3] [4] Even so, spider cannibalism has been shown to occur in some species more than in others, mainly species belonging to Latrodectus.
There has always been speculation on why this sacrifice of male mates might occur despite the obvious disadvantage to the sacrificial males. One theory is that once the male has mated, he is unlikely to mate again and so any further extension of his life is of lesser evolutionary benefit than his indirectly contributing nutrition to the eggs. Having more offspring would give the male the advantage of having his genes passed on over other males that might avoid being eaten, which is consistent with one hypothesis that old or unfit males get eaten, whilst younger and fitter ones may survive to mate again. [4]
Reversing the traditional roles, species that have males consuming females are relatively unknown; the few that do show a male-biased sexual dimorphism. Examples include Allocosa brasiliensis , Evarcha culicivora , and Argyronetia aquatica. Male water spiders, Argyronetia aquatica, show a predilection for mating with larger females, while cannibalizing females smaller than themselves. [5]
As is the case with Allocosa brasiliensis, males cull older females who are less fertile than their young counterparts.
Juvenile redback spiders live in groups immediately after hatching, and are known to cannibalize siblings during this period. Cannibalism is a heritable trait in these spiders, with some families more prone to it than others. [6]
Some spiders, such as Pholcus phalangioides , will prey on their own kind when food is scarce. Also, females of Phidippus johnsoni have been observed carrying dead males in their fangs. This behavior may be triggered by aggression, where females carry over hostility from their juvenile state and consume males just as they would prey. It has been surmised that non-reproductive cannibalism can occur due to a remnant of an aggression trait in juvenile females. Known as the "aggressive spillover hypothesis", this tendency to unselectively attack anything that moves is cultivated by a positive correlation between hostility, foraging capability, and fecundity. Aggression at a young age leads to an increase in prey consumption and as such, a larger adult size. This behavior "spills over" into adulthood, and shows up as a nonadaptive trait that manifests itself through adult females preying on males of their same species. [7]
Latrodectus is a broadly distributed genus of spiders with several species that are commonly known as the true widows. This group is composed of those often loosely called black widow spiders, brown widow spiders, and similar spiders. However, the diversity of species is much greater. A member of the family Theridiidae, this genus contains 34 species, which include several North American "black widows". Besides these, North America also has the red widow Latrodectus bishopi and the brown widow Latrodectus geometricus, which, in addition to North America, has a much wider geographic distribution. Elsewhere, others include the European black widow, the Australian redback spider and the closely related New Zealand katipō, several different species in Southern Africa that can be called button spiders, and the South American black-widow spiders. Species vary widely in size. In most cases, the females are dark-coloured and can be readily identified by reddish markings on the central underside (ventral) abdomen, which are often hourglass-shaped.
The redback spider, also known as the Australian black widow, is a species of highly venomous spider believed to originate in South Australia or adjacent Western Australian deserts, but now found throughout Australia, Southeast Asia and New Zealand, with colonies elsewhere outside Australia. It is a member of the cosmopolitan genus Latrodectus, the widow spiders. The adult female is easily recognised by her spherical black body with a prominent red stripe on the upper side of her abdomen and an hourglass-shaped red/orange streak on the underside. Females usually have a body length of about 10 millimetres (0.4 in), while the male is much smaller, being only 3–4 mm (0.12–0.16 in) long.
The raft spider, scientific name Dolomedes fimbriatus, is a large semi-aquatic spider of the family Pisauridae found throughout north-western and central Europe. It is one of only two species of the genus Dolomedes found in Europe, the other being the slightly larger Dolomedesplantarius which is endangered in the UK.
Latrodectus hesperus, the western black widow spider or western widow, is a venomous spider species found in western regions of North America. The female's body is 14–16 mm in length and is black, often with an hourglass-shaped red mark on the lower abdomen. This "hourglass" mark can be yellow, and on rare occasions, white. The male of the species is around half this length and generally a tan color with lighter striping on the abdomen. The population was previously described as a subspecies of Latrodectus mactans and it is closely related to the northern species Latrodectus variolus. The species, as with others of the genus, build irregular or "messy" webs: unlike the spiral webs or the tunnel-shaped webs of other spiders, the strands of a Latrodectus web have no apparent organization.
Misumena vatia is a species of crab spider with a holarctic distribution. In North America, it is called the goldenrod crab spider or flower (crab) spider, as it is commonly found hunting in goldenrod sprays and milkweed plants. They are called crab spiders because of their unique ability to walk sideways as well as forwards and backwards. Both males and females of this species progress through several molts before reaching their adult sizes, though females must molt more to reach their larger size. Females can grow up to 10 mm (0.39 in) while males are quite small, reaching 5 mm (0.20 in) at most. Misumena vatia are usually yellow or white or a pattern of these two colors. They may also present with pale green or pink instead of yellow, again, in a pattern with white. They have the ability to change between these colors based on their surroundings through the molting process. They have a complex visual system, with eight eyes, that they rely on for prey capture and for their color-changing abilities. Sometimes, if Misumena vatia consumes colored prey, the spider itself will take on that color.
Spider behavior refers to the range of behaviors and activities performed by spiders. Spiders are air-breathing arthropods that have eight legs and chelicerae with fangs that inject venom. They are the largest order of arachnids and rank seventh in total species diversity among all other groups of organisms which is reflected in their large diversity of behavior.
Cannibalism is the act of consuming another individual of the same species as food. Cannibalism is a common ecological interaction in the animal kingdom and has been recorded in more than 1,500 species. Human cannibalism is well documented, both in ancient and in recent times.
Sexual cannibalism is when an animal, usually the female, cannibalizes its mate prior to, during, or after copulation. It is a trait observed in many arachnid orders, several insect and crustacean clades, gastropods, and some snake species. Several hypotheses to explain this seemingly paradoxical behavior have been proposed. The adaptive foraging hypothesis, aggressive spillover hypothesis and mistaken identity hypothesis are among the proposed hypotheses to explain how sexual cannibalism evolved. This behavior is believed to have evolved as a manifestation of sexual conflict, occurring when the reproductive interests of males and females differ. In many species that exhibit sexual cannibalism, the female consumes the male upon detection. Females of cannibalistic species are generally hostile and unwilling to mate; thus many males of these species have developed adaptive behaviors to counteract female aggression.
Trichonephila plumipes, the Pacific golden orb weaver, is a species of spider found in Australia, Indonesia and some Pacific Islands, which exhibits extreme sexual dimorphism through its sexual cannibalism behavior. It is sometimes called the tiger spider due to its markings which look similar to a tiger. This species was formerly called Nephila plumipes. As with other spiders from the genus Nephila, these spiders have a distinct golden web.
Monogyny is a specialised mating system in which a male can only mate with one female throughout his lifetime, but the female may mate with more than one male. In this system, the males generally provide no paternal care. In many spider species that are monogynous, the males have two copulatory organs, which allows them to mate a maximum of twice throughout their lifetime. As is commonly seen in honeybees, ants and certain spider species, a male may put all his energy into a single copulation, knowing that this will lower his overall fitness. During copulation, monogynous males have adapted to cause self genital damage or even death to increase their chances of paternity.
The six-spotted fishing spider is an arachnid from the nursery web spider family Pisauridae. This species is from the genus Dolomedes, or the fishing spiders. Found in wetland habitats throughout North America, these spiders are usually seen scampering along the surface of ponds and other bodies of water. They are also referred to as dock spiders because they can sometimes be witnessed quickly vanishing through the cracks of boat docks. D. triton gets its scientific name from the Greek mythological god Triton, who is the messenger of the big sea and the son of Poseidon.
Allocosa brasiliensis is a burrowing wolf spider species from southern South America. Long known to science, it remained almost unstudied until its unusual sexual behavior was described in the early 21st century.
Pisaurina mira, also known as the American nursery web spider, is a species of spider in the family Pisauridae. They are often mistaken for wolf spiders (Lycosidae) due to their physical resemblance. P. mira is distinguished by its unique eye arrangement of two rows.
Sexual selection in spiders shows how sexual selection explains the evolution of phenotypic traits in spiders. Male spiders have many complex courtship rituals and have to avoid being eaten by the females, with the males of most species surviving only a few matings and consequently having short life-spans.
Tigrosa helluo is a species of spider belonging to the family Lycosidae, also known as wolf spiders. T. helluo was formerly known as Hogna helluo before differences between dorsal color patterns, habitat preferences, body structures, etc. were discovered. The species is native to the United States, Canada, and Mexico. It can be found across the eastern half of the United States, primarily in the Northeast and New England, and as far west as Nebraska and Kansas. T. helluo can be found in diverse habitats including woods, marshes, fields, and riparian areas. Typically, members of this species prefer to live in wetter areas as opposed to dry environments. Males tend to live for around a year and females will live for close to two years.
Agelenopsis pennsylvanica, commonly known as the Pennsylvania funnel-web spider or the Pennsylvania grass spider, is a species of spider in the family Agelenidae. The common name comes from the place that it was described, Pennsylvania, and the funnel shape of its web. Its closest relative is Agelenopsis potteri.
Maydianne Andrade is a Jamaican-born Canadian ecologist. She is known for her work on the mating habits of spiders, in particular spiders belonging to the Latrodectus species. In 2007, she was named a Canadian Research Chair in Integrative Behavioural Ecology.
Pardosa agrestis is a non-web-building spider in the family Lycosidae, commonly known as wolf spiders.
Latrodectus revivensis, also known as the desert widow, is a species of venomous spider belonging to the Latrodectus genus and located in the Negev desert and the Arava valley (Arabah).
Pardosa pseudoannulata, a member of a group of species referred to as wolf-spiders, is a non-web-building spider belonging to the family Lycosidae. P. pseudoannulata are wandering spiders that track and ambush prey and display sexual cannibalism. They are commonly encountered in farmlands across China and other East Asian countries. Their venom has properties that helps it function as an effective insecticide, and it is, therefore, a crucial pesticide control agent.
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