Spider cannibalism

Spider cannibalism

Spider cannibalism is a special case of cannibalism in which a female spider kills and eats a male of the same species before, during, or after copulation. Rarely, these roles are reversed...

 is a special case of cannibalism

Cannibalism

Cannibalism is the act or practice of humans eating the flesh of other human beings. It is also called anthropophagy...

 in which a female

Female

Female is the sex of an organism, or a part of an organism, which produces non-mobile ova .- Defining characteristics :The ova are defined as the larger gametes in a heterogamous reproduction system, while the smaller, usually motile gamete, the spermatozoon, is produced by the male...

 spider kills and eats a male

Male

Male refers to the biological sex of an organism, or part of an organism, which produces small mobile gametes, called spermatozoa. Each spermatozoon can fuse with a larger female gamete or ovum, in the process of fertilization...

 of the same species

Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 before, during, or after copulation. Rarely, these roles are reversed. While there are some species

Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 where sexual cannibalism

Cannibalism

Cannibalism is the act or practice of humans eating the flesh of other human beings. It is also called anthropophagy...

 is normal, the aforementioned reversal of roles is abnormal in all.

It is often said that the male (usually significantly smaller than the female, down to 1% of her size as seen in Tidarren sisyphoides

Tidarren sisyphoides

Tidarren sisyphoides is a spider of the family Theridiidae .The male of this species is only 1% the size of the female. At copulation, the male dies during insertion and remains attached to the female for more than two hours. However, the female does not eat her mate. The dead male is afterwards...

) 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 America

North America

North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...

n black widows do not seem to usually kill the male (although they have been known to). Males can sometimes even live in the web of a female for a while without being harmed in any way. The male Australian redback spider Latrodectus hasselti is killed by the females after it inserts its 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 it, this species represents a possible strategy of "male sacrifice". The male redback, while copulating, 'somersaults' and twists its abdomen directly onto the fangs of its mate. Most males get consumed at this stage (Maydianne CB Andrade reports 65%). Males that 'sacrifice' themselves gain the benefit of increasing their paternity relative to males who do not get cannibalized.

However, despite these examples and many other similar reports, the theory of the 'sacrificial male' has become greater than the truth. Mating of spiders is not always followed by cannibalism. Foelix writes, "The supposed aggressiveness of the female spider towards the male is largely a myth... only in some exceptional cases does the male fall victim to the female." Michael Roberts says, "It is rare for a fit male to be eaten by the female." And yet, spider cannibalism has been proved 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 fact that there is an 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 evolution

Evolution

Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...

ary benefit than his indirectly contributing nutrition

Nutrition

Nutrition is the provision, to cells and organisms, of the materials necessary to support life. Many common health problems can be prevented or alleviated with a healthy diet....

 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. This scenario would be consistent with the hypothesis of Roberts that old or unfit males get eaten, whilst younger and fitter ones may survive to mate again.

Non-reproductive cannibalism

Some spiders, such as Pholcus phalangioides

Pholcus phalangioides

The cellar spider or daddy longlegs , also known as the skull spider due to its cephalothorax looking like a human skull, is a spider of the family Pholcidae. Females have a body length of about 9 mm; males are slightly smaller. Its legs are about 5 or 6 times the length of its body...

, will prey on their own kind when food is scarce. Also, females of Phidippus johnsoni

Phidippus johnsoni

The red-backed jumping spider is one of the largest and most commonly encountered jumping spiders of western North America. It is not to be confused with the unrelated and highly venomous redback spider...

have been observed carrying dead males in their fangs.