Allocosa brasiliensis
Encyclopedia
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.
This ground-dwelling spider is native to mainly coastal areas, from southeastern Brazil
via Uruguay
and Argentina
to southern Chile
, though its known occurrences are patchy. To what extent it is found on the Atlantic coast south of the Río de la Plata
remains largely unknown, for example. While the males have been known for over a century, the females were only described in 1980.
light brown spider of robust build, with a body size of well over 1 cm (0.5 in and more) when fully grown, up to almost twice this size in the largest specimens. The cephalothorax
has an inconspicuous darker stripe pattern reminiscent of that found in many lycosids, but the opisthosoma
is patterned with yellower and darker spots the approximate size of sand grains. Males and females look alike in color, but differ in size and genitals.
Adult females have a cephalothorax carapace some 4–5 mm wide and some 6–7 mm long on average. Quite unusually for spiders in general, adult males are about 20% larger. Still, as usual for wolf spiders the females are more robustly built, wider-bodied and shorter-legged. In both sexes the four middle legs are shortest, the hind pair longest and the front pair intermediate. Even the shortest four legs of the adult females usually measure more than 1 cm. The longest leg pair is usually 2 cm or more in adult males and may measure up to about 2.5 cm (1 in). In females, it may grow to almost 1 in, but is usually around 2 cm.
in 1909 by Russian-American arachnologist A. Petrunkevitch
; the description was based on a male from Brazil
and published in the Academy's annual volume
released in 1910. Petrunkevitch placed the species
in a new genus
Moenkhausiana, due to its unusual and distinct spinneret
s and leg proportions. Initially considered monotypic
, C.F. de Mello-Leitão
later described a presumed relative "M." argentinensis.
But soon thereafter, when he studied spiders from northern Argentina
, he became so convinced of their distinctness as to consider them ant spiders (Zodariidae) and in 1945 re-described the present species as Glieschiella senex, perhaps not recognizing it because he misidentified his specimen as a female (it was actually also a male, like the type specimen of A. brasiliensis). In the supposed ant spider genus, it was associated with "G." alticeps (see below) and the type species of Glieschiella, "G." halophila.
Yet in 1951 Mello-Leitão, when studying some spiders caught at Maullin
(Chile
), again described A. brasiliensis anew, in yet another monotypic
genus Araucaniocosa. Subsequently it was mainly studied under the 1951 name – Araucaniocosa difficilis –, and affiliated closely with the "European tarantulas" (Lycosa
), even included there as a sub-genus. When the females were first described, they were also treated under the 1951 name, as they were also based on individuals from Chile.
Today, Moenkhausiana and Glieschiella are treated as junior synonym of the large genus Allocosa
, which is not considered to be very close to Lycosa as wolf spiders go. As regards the species which were historically affiliated with A. brasiliensis, A. alticeps is generally considered valid, while "A. argentinensis" and "A. halophila" are apparently based on immature specimens and considered nomina dubia
. The former at least was described from outside the known range of A. brasiliensis – from Isla Tehuel Malal, Río Negro Province
, southeastern Argentina –, but restudy would be needed to determine whether any of them is a distinct taxon
. Whether the (possibly widely allopatric) Chilean population is a taxonomically distinct subspecies
has not been studied in detail; certainly however, it does not seem to be a distinct species and has no conspicuous difference in size.
. The burrows of adults are quite exactly 1 cm wide and usually run steeply down, with a length of a few cm (1–3 in). Male burrows tend to be longer/deeper, up to 10 cm and more (4 in). The spiders are more frequently found on the land-side of dunes, which is better protected
against strong winds, and prefer open habitat to vegetation when outside their burrows. The reproductive peak takes place in January (after midsummer), with the highest surface and foraging activity shown during Southern hemisphere summer.
In general, the habitat is cool and humid for its region, at best subtropical, the air being constantly moistened, usually by brine
that is carried from the sea by the wind. In typical habitat at El Pinar, Uruguay
, average air and ground temperatures were measured just around 20 °C (68 °F) in November (early summer). Relative humidity
was almost 100%, even though the air was constantly exchanged even in the area of ground effect
. The vegetation was rather monotonous, dominated by ragwort
(Senecio) and Panicum
grass. Potential A. brasiliensis prey that was commonly encountered were Acromyrmex
ants, Tetragonoderus
ground beetle
s and striped earwigs of genus Labidura. Rhino beetles of the genus Thronistes were also common in that habitat, but presumably too tough for the spiders to eat. As a possible predator of the spiders, a dune-adapted species of tree iguana (Liolaemus) was noted.
Owing to its harsh habitat, with high variability of weather conditions and prey availability, A. brasiliensis is a highly opportunistic free-roaming predator, feeding mostly on spider
s, beetle
s, flies
and ant
s. Altogether, the species prefers to feed on spiders, which make up about one-third of its diet; indeed, other Allocosa are typically eaten more often than any other kind of prey during the life of any wild-living A. brasiliensis. But the mainstay food actually varies quite a lot between the seasons, and in general these spider's food choice is shaped by availability more than by preference. Less frequently other arthropod
s are caught, e.g. true bugs (Hemiptera) or crickets, grasshoppers etc. (Orthoptera
). Ants such as Acromyrmex or Dorymyrmex
are often caught on their trails or during their nuptial flight
s, and the nimble and well-camouflaged spiders manage to surprise Lepidoptera
(butterflies and moths) resting on the ground surprisingly often. As regards cannibalism
, the adult female A. brasiliensis are if anything less prone to eat conspecifics than spiders in general, let alone the adult females which in many species are famous
for habitually feeding on their mates. In A. brasiliensis by contrast, immatures are voraciously cannibalistic on each other and even more often eat females of the smaller sympatric relative A. alticeps. Most remarkably however, the adult males include a considerable number of conspecific females in their diet.
Adults reach maturity at around 9–10 months of age and after around 10 (up to one dozen) moult
s; females grow up somewhat faster than males, and often have one moult less. On average females tend to be slightly shorter-lived than males at least in captivity, where the latter typically live for almost 500 days. An extreme age of almost 2 years has been recorded in a captive female; generally the species seems to be semelparous
.
In captivity, these spiders have been maintained from wild-collected eggs to maturity and senescence
in petri dish
es, one spider per dish. A thin layer of sea sand and a watered lump of clean cotton wool create a favorable microclimate
and allow the spiders to drink. Spiderling
s fared well in dishes of 3.5 cm diameter and about 1 cm height; as they grow (around the third to fourth instar
) they will need to be housed in larger dishes (about 10 cm in diameter and over 1 cm in height). As captive-bred food, Drosophila
flies up to the fourth instar and subsequently Tenebrio mealworm
s of appropriate size, and for adults also small Orange-spotted Cockroaches (Blaptica dubia), were used with success. Adults will need three such food items per week. Captive breeding attempts require sizeable terraria due to the spiders' burrowing and cannibalistic habits; a 15-cm (>5 in) sand bottom with 5 cm (2 in) air above has been found to work; the base area should not be much less than 450 cm2 (0.5 ft2). The mating terrarium needs to be divided by a barrier, the above ground part of which is removed when male and female have constructed their burrow.
on older females that were lured into the male's burrow, while preferring mating with virgins. The first egg sac of A. brasiliensis females contains more eggs than later ones, which, together with the harsh habitat, gives this behavior an evolutionary advantage.
The smaller and stronger-marked relative Allocosa alticeps, which lives sympatrically in the same habitat, seems to show a similar sexual role reversal. Although cannibalism is not rare among spiders, the selective hunting of females by males is as of 2010 unknown in any other spider species; even A. alticeps does not seem to be conspicuously cannibalistic.
These Allocosa are the only known wolf spiders adapted to living on the Uruguay
an coastline (though see above for possible relatives). Sexual size dimorphism seems to be more pronounced in A. brasiliensis, while A. alticeps females and males are often enough about the same size. Both sexes of the present species are usually found equally frequently; in A. alticeps females appear to outnumber males by far. Reproductive isolation
is ultimately achieved via behavior and genital anatomy
, but quite often inspecting the differently-sized and differently-smelling
burrow entrance will already allow these spiders to identify conspecifics. In addition, the species also seem to have different microhabitat preferences.
44(19-20): 1189-1202. (HTML abstract) (2011): Spatial distribution, burrow depth and temperature: implications for the sexual strategies in two Allocosa wolf spiders. Studies on Neotropical Fauna and Environment 46(2): 147–152.
Wolf spider
Wolf spiders are members of the family Lycosidae, from the Ancient Greek word "" meaning "wolf". They are robust and agile hunters with good eyesight. They live mostly solitary lives and hunt alone. Some are opportunistic hunters pouncing upon prey as they find it or even chasing it over short...
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...
from southern South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
. Long known to science, it remained almost unstudied until its unusual sexual behavior was described in the early 21st century.
This ground-dwelling spider is native to mainly coastal areas, from southeastern Brazil
Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...
via Uruguay
Uruguay
Uruguay ,officially the Oriental Republic of Uruguay,sometimes the Eastern Republic of Uruguay; ) is a country in the southeastern part of South America. It is home to some 3.5 million people, of whom 1.8 million live in the capital Montevideo and its metropolitan area...
and Argentina
Argentina
Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...
to southern Chile
Chile
Chile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...
, though its known occurrences are patchy. To what extent it is found on the Atlantic coast south of the Río de la Plata
Río de la Plata
The Río de la Plata —sometimes rendered River Plate in British English and the Commonwealth, and occasionally rendered [La] Plata River in other English-speaking countries—is the river and estuary formed by the confluence of the Uruguay River and the Paraná River on the border between Argentina and...
remains largely unknown, for example. While the males have been known for over a century, the females were only described in 1980.
Description
A. brasiliensis is a mid-sized crypticCrypsis
In ecology, crypsis is the ability of an organism to avoid observation or detection by other organisms. It may be either a predation strategy or an antipredator adaptation, and methods include camouflage, nocturnality, subterranean lifestyle, transparency, and mimicry...
light brown spider of robust build, with a body size of well over 1 cm (0.5 in and more) when fully grown, up to almost twice this size in the largest specimens. The cephalothorax
Cephalothorax
The cephalothorax is a tagma of various arthropods, comprising the head and the thorax fused together, as distinct from the abdomen behind. The word cephalothorax is derived from the Greek words for head and thorax...
has an inconspicuous darker stripe pattern reminiscent of that found in many lycosids, but the opisthosoma
Opisthosoma
The opisthosoma is the posterior part of the body in some arthropods, behind the prosoma . It is a distinctive feature of the subphylum Chelicerata...
is patterned with yellower and darker spots the approximate size of sand grains. Males and females look alike in color, but differ in size and genitals.
Adult females have a cephalothorax carapace some 4–5 mm wide and some 6–7 mm long on average. Quite unusually for spiders in general, adult males are about 20% larger. Still, as usual for wolf spiders the females are more robustly built, wider-bodied and shorter-legged. In both sexes the four middle legs are shortest, the hind pair longest and the front pair intermediate. Even the shortest four legs of the adult females usually measure more than 1 cm. The longest leg pair is usually 2 cm or more in adult males and may measure up to about 2.5 cm (1 in). In females, it may grow to almost 1 in, but is usually around 2 cm.
Taxonomy
A. brasiliensis was first described to the New York Academy of SciencesNew York Academy of Sciences
The New York Academy of Sciences is the third oldest scientific society in the United States. An independent, non-profit organization with more than members in 140 countries, the Academy’s mission is to advance understanding of science and technology...
in 1909 by Russian-American arachnologist A. Petrunkevitch
Alexander Petrunkevitch
Alexander Ivanovitch Petrunkevitch was an eminent arachnologist of his time. From 1910 to 1939 he described over 130 spider species.-Biography:...
; the description was based on a male from Brazil
Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...
and published in the Academy's annual volume
Annals of the New York Academy of Sciences
The Annals of the New York Academy of Sciences is an academic journal published by the New York Academy of Sciences. It is one of the oldest science journals, being founded in 1823....
released in 1910. Petrunkevitch placed the 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...
in a new genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
Moenkhausiana, due to its unusual and distinct spinneret
Spinneret
A spinneret is a spider's or insect larva's silk-spinning organ. It is usually on the underside of a spider's abdomen, to the rear. While most spiders have six spinnerets, some have two, four, or eight. They move independently and in concert...
s and leg proportions. Initially considered monotypic
Monotypic
In biology, a monotypic taxon is a taxonomic group with only one biological type. The term's usage differs slightly between botany and zoology. The term monotypic has a separate use in conservation biology, monotypic habitat, regarding species habitat conversion eliminating biodiversity and...
, C.F. de Mello-Leitão
Cândido Firmino de Mello-Leitão
Cândido Firmino de Mello-Leitão, , was a Brazilian zoologist who is considered the founder of Arachnology in South America, publishing 198 papers on the taxonomy of Arachnida...
later described a presumed relative "M." argentinensis.
But soon thereafter, when he studied spiders from northern Argentina
Argentina
Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...
, he became so convinced of their distinctness as to consider them ant spiders (Zodariidae) and in 1945 re-described the present species as Glieschiella senex, perhaps not recognizing it because he misidentified his specimen as a female (it was actually also a male, like the type specimen of A. brasiliensis). In the supposed ant spider genus, it was associated with "G." alticeps (see below) and the type species of Glieschiella, "G." halophila.
Yet in 1951 Mello-Leitão, when studying some spiders caught at Maullin
Maullín
Maullín is Chilean town and commune in Llanquihue Province which is part of Los Lagos Region. The commune is located in at the outflow of Maullín River.-History:In 1674, there was a group of soldiers Basques in the present position of the commune...
(Chile
Chile
Chile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...
), again described A. brasiliensis anew, in yet another monotypic
Monotypic
In biology, a monotypic taxon is a taxonomic group with only one biological type. The term's usage differs slightly between botany and zoology. The term monotypic has a separate use in conservation biology, monotypic habitat, regarding species habitat conversion eliminating biodiversity and...
genus Araucaniocosa. Subsequently it was mainly studied under the 1951 name – Araucaniocosa difficilis –, and affiliated closely with the "European tarantulas" (Lycosa
Lycosa
Lycosa is a genus of wolf spiders. More than 200 species are found, represented throughout most of the world. Often called the "true tarantula", Lycosa can be distinguished from common wolf spiders by their relatively large size...
), even included there as a sub-genus. When the females were first described, they were also treated under the 1951 name, as they were also based on individuals from Chile.
Today, Moenkhausiana and Glieschiella are treated as junior synonym of the large genus Allocosa
Allocosa
Allocosa is a spider genus of the Lycosidae family . The about 140 recognized species are spread worldwide.-Species:* Allocosa abmingani — South Australia* Allocosa absoluta — USA, Mexico...
, which is not considered to be very close to Lycosa as wolf spiders go. As regards the species which were historically affiliated with A. brasiliensis, A. alticeps is generally considered valid, while "A. argentinensis" and "A. halophila" are apparently based on immature specimens and considered nomina dubia
Nomen dubium
In zoological nomenclature, a nomen dubium is a scientific name that is of unknown or doubtful application...
. The former at least was described from outside the known range of A. brasiliensis – from Isla Tehuel Malal, Río Negro Province
Río Negro Province
Río Negro is a province of Argentina, located at the northern edge of Patagonia. Neighboring provinces are from the south clockwise Chubut, Neuquén, Mendoza, La Pampa and Buenos Aires. To the east lies the Atlantic Ocean.Its capital is Viedma...
, southeastern Argentina –, but restudy would be needed to determine whether any of them is a distinct taxon
Taxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...
. Whether the (possibly widely allopatric) Chilean population is a taxonomically distinct subspecies
Subspecies
Subspecies in biological classification, is either a taxonomic rank subordinate to species, ora taxonomic unit in that rank . A subspecies cannot be recognized in isolation: a species will either be recognized as having no subspecies at all or two or more, never just one...
has not been studied in detail; certainly however, it does not seem to be a distinct species and has no conspicuous difference in size.
Ecology and behavior
A. brasiliensis is nocturnal, resting at daytime in burrows in sand dunes along river mouths and the coast of at least part of the Southern ConeSouthern Cone
Southern Cone is a geographic region composed of the southernmost areas of South America, south of the Tropic of Capricorn. Although geographically this includes part of Southern and Southeast of Brazil, in terms of political geography the Southern cone has traditionally comprised Argentina,...
. The burrows of adults are quite exactly 1 cm wide and usually run steeply down, with a length of a few cm (1–3 in). Male burrows tend to be longer/deeper, up to 10 cm and more (4 in). The spiders are more frequently found on the land-side of dunes, which is better protected
Windward and leeward
Windward is the direction upwind from the point of reference. Leeward is the direction downwind from the point of reference. The side of a ship that is towards the leeward is its lee side. If the vessel is heeling under the pressure of the wind, this will be the "lower side"...
against strong winds, and prefer open habitat to vegetation when outside their burrows. The reproductive peak takes place in January (after midsummer), with the highest surface and foraging activity shown during Southern hemisphere summer.
In general, the habitat is cool and humid for its region, at best subtropical, the air being constantly moistened, usually by brine
Brine
Brine is water, saturated or nearly saturated with salt .Brine is used to preserve vegetables, fruit, fish, and meat, in a process known as brining . Brine is also commonly used to age Halloumi and Feta cheeses, or for pickling foodstuffs, as a means of preserving them...
that is carried from the sea by the wind. In typical habitat at El Pinar, Uruguay
El Pinar, Uruguay
El Pinar is a seaside resort of the Canelones Department, Uruguay. In 1994, when Ciudad de la Costa took on the status of a city, El Pinar was incorporated in it.-Geography:...
, average air and ground temperatures were measured just around 20 °C (68 °F) in November (early summer). Relative humidity
Relative humidity
Relative humidity is a term used to describe the amount of water vapor in a mixture of air and water vapor. It is defined as the partial pressure of water vapor in the air-water mixture, given as a percentage of the saturated vapor pressure under those conditions...
was almost 100%, even though the air was constantly exchanged even in the area of ground effect
Ground effect
As it pertains to fixed wing aircraft, "ground effect" refers to the increased lift and decreased drag that an aircraft airfoil or wing generates when an aircraft is about one wingspan's length or less over the ground...
. The vegetation was rather monotonous, dominated by ragwort
Ragwort
Ragwort is a very common wild flower in the family Asteraceae that is native to northern Eurasia, usually in dry, open places, and has also been widely distributed as a weed elsewhere....
(Senecio) and Panicum
Panicum
Panicum is a large genus of about 450 species of grasses native throughout the tropical regions of the world, with a few species extending into the northern temperate zone...
grass. Potential A. brasiliensis prey that was commonly encountered were Acromyrmex
Acromyrmex
Acromyrmex is a genus of New World ants of the subfamily Myrmicinae. It contains 31 known species.-Distribution:This genera is found in South America and parts of Central America and the Caribbean islands.-Overview:...
ants, Tetragonoderus
Tetragonoderus
Tetragonoderus is a genus of beetles in the family Carabidae, containing the following species:* Tetragonoderus aegypticus Jedlicka, 1952 * Tetragonoderus aericollis Quedenfeldt, 1883 * Tetragonoderus andrewesi Emden, 1934...
ground beetle
Ground beetle
Ground beetles are a large, cosmopolitan family of beetles, Carabidae, with more than 40,000 species worldwide, approximately 2,000 of which are found in North America and 2,700 in Europe.-Description and ecology:...
s and striped earwigs of genus Labidura. Rhino beetles of the genus Thronistes were also common in that habitat, but presumably too tough for the spiders to eat. As a possible predator of the spiders, a dune-adapted species of tree iguana (Liolaemus) was noted.
Owing to its harsh habitat, with high variability of weather conditions and prey availability, A. brasiliensis is a highly opportunistic free-roaming predator, feeding mostly on spider
Spider
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...
s, beetle
Beetle
Coleoptera is an order of insects commonly called beetles. The word "coleoptera" is from the Greek , koleos, "sheath"; and , pteron, "wing", thus "sheathed wing". Coleoptera contains more species than any other order, constituting almost 25% of all known life-forms...
s, flies
Fly
True flies are insects of the order Diptera . They possess a pair of wings on the mesothorax and a pair of halteres, derived from the hind wings, on the metathorax...
and ant
Ant
Ants are social insects of the family Formicidae and, along with the related wasps and bees, belong to the order Hymenoptera. Ants evolved from wasp-like ancestors in the mid-Cretaceous period between 110 and 130 million years ago and diversified after the rise of flowering plants. More than...
s. Altogether, the species prefers to feed on spiders, which make up about one-third of its diet; indeed, other Allocosa are typically eaten more often than any other kind of prey during the life of any wild-living A. brasiliensis. But the mainstay food actually varies quite a lot between the seasons, and in general these spider's food choice is shaped by availability more than by preference. Less frequently other arthropod
Arthropod
An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...
s are caught, e.g. true bugs (Hemiptera) or crickets, grasshoppers etc. (Orthoptera
Orthoptera
Orthoptera is an order of insects with paurometabolous or incomplete metamorphosis, including the grasshoppers, crickets and locusts.Many insects in this order produce sound by rubbing their wings against each other or their legs, the wings or legs containing rows of corrugated bumps...
). Ants such as Acromyrmex or Dorymyrmex
Dorymyrmex
Dorymyrmex is a genus of Dolichoderinae known as the cone ant. Sometimes referred to as the "odorous ant" because of a distinct smell many have, which resembles the scent of blue cheese....
are often caught on their trails or during their nuptial flight
Nuptial flight
Nuptial flight is an important phase in the reproduction of most ant, termite and some bee species. During the flight, virgin queens mate with males and then land to start a new colony, or, in the case of honey bees, continue the planned succession of an existing hived colony.- Before the flight :A...
s, and the nimble and well-camouflaged spiders manage to surprise Lepidoptera
Lepidoptera
Lepidoptera is a large order of insects that includes moths and butterflies . It is one of the most widespread and widely recognizable insect orders in the world, encompassing moths and the three superfamilies of butterflies, skipper butterflies, and moth-butterflies...
(butterflies and moths) resting on the ground surprisingly often. As regards cannibalism
Cannibalism
Cannibalism is the act or practice of humans eating the flesh of other human beings. It is also called anthropophagy...
, the adult female A. brasiliensis are if anything less prone to eat conspecifics than spiders in general, let alone the adult females which in many species are famous
Black Widow
Black widow is a common name of some spiders in the genus Latrodectus.Black Widow may also refer to:-Fiction:* Black Widow: A Novel, a 1981 novel by Christina Crawford...
for habitually feeding on their mates. In A. brasiliensis by contrast, immatures are voraciously cannibalistic on each other and even more often eat females of the smaller sympatric relative A. alticeps. Most remarkably however, the adult males include a considerable number of conspecific females in their diet.
Adults reach maturity at around 9–10 months of age and after around 10 (up to one dozen) moult
Moult
In biology, moulting or molting , also known as sloughing, shedding, or for some species, ecdysis, is the manner in which an animal routinely casts off a part of its body , either at specific times of year, or at specific points in its life cycle.Moulting can involve the epidermis , pelage...
s; females grow up somewhat faster than males, and often have one moult less. On average females tend to be slightly shorter-lived than males at least in captivity, where the latter typically live for almost 500 days. An extreme age of almost 2 years has been recorded in a captive female; generally the species seems to be semelparous
Semelparity and iteroparity
Semelparity and Iteroparity refer to the reproductive strategy of an organism. A species is considered semelparous if it is characterized by a single reproductive episode before death, and iteroparous if it is characterized by multiple reproductive cycles over the course of its lifetime. Some...
.
In captivity, these spiders have been maintained from wild-collected eggs to maturity and senescence
Senescence
Senescence or biological aging is the change in the biology of an organism as it ages after its maturity. Such changes range from those affecting its cells and their function to those affecting the whole organism...
in petri dish
Petri dish
A Petri dish is a shallow glass or plastic cylindrical lidded dish that biologists use to culture cells or small moss plants. It was named after German bacteriologist Julius Richard Petri, who invented it when working as an assistant to Robert Koch...
es, one spider per dish. A thin layer of sea sand and a watered lump of clean cotton wool create a favorable microclimate
Microclimate
A microclimate is a local atmospheric zone where the climate differs from the surrounding area. The term may refer to areas as small as a few square feet or as large as many square miles...
and allow the spiders to drink. Spiderling
Spiderling
Spiderling may refer to:* an immature spider* the herbaceous plant genus Boerhavia...
s fared well in dishes of 3.5 cm diameter and about 1 cm height; as they grow (around the third to fourth instar
Instar
An instar is a developmental stage of arthropods, such as insects, between each molt , until sexual maturity is reached. Arthropods must shed the exoskeleton in order to grow or assume a new form. Differences between instars can often be seen in altered body proportions, colors, patterns, or...
) they will need to be housed in larger dishes (about 10 cm in diameter and over 1 cm in height). As captive-bred food, Drosophila
Drosophila
Drosophila is a genus of small flies, belonging to the family Drosophilidae, whose members are often called "fruit flies" or more appropriately pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many species to linger around overripe or rotting fruit...
flies up to the fourth instar and subsequently Tenebrio mealworm
Mealworm
Mealworms are the larval form of the mealworm beetle, Tenebrio molitor, a species of darkling beetle. Like all holometabolic insects, they go through four life stages: egg, larva, pupa, and adult...
s of appropriate size, and for adults also small Orange-spotted Cockroaches (Blaptica dubia), were used with success. Adults will need three such food items per week. Captive breeding attempts require sizeable terraria due to the spiders' burrowing and cannibalistic habits; a 15-cm (>5 in) sand bottom with 5 cm (2 in) air above has been found to work; the base area should not be much less than 450 cm2 (0.5 ft2). The mating terrarium needs to be divided by a barrier, the above ground part of which is removed when male and female have constructed their burrow.
Sexual role reversal
A. brasiliensis males use pheromones to attract females, in contrast to most other burrowing wolf spiders, where the females attract the males. Males have been observed to specifically cannibalizeCannibalism
Cannibalism is the act or practice of humans eating the flesh of other human beings. It is also called anthropophagy...
on older females that were lured into the male's burrow, while preferring mating with virgins. The first egg sac of A. brasiliensis females contains more eggs than later ones, which, together with the harsh habitat, gives this behavior an evolutionary advantage.
The smaller and stronger-marked relative Allocosa alticeps, which lives sympatrically in the same habitat, seems to show a similar sexual role reversal. Although cannibalism is not rare among spiders, the selective hunting of females by males is as of 2010 unknown in any other spider species; even A. alticeps does not seem to be conspicuously cannibalistic.
These Allocosa are the only known wolf spiders adapted to living on the Uruguay
Uruguay
Uruguay ,officially the Oriental Republic of Uruguay,sometimes the Eastern Republic of Uruguay; ) is a country in the southeastern part of South America. It is home to some 3.5 million people, of whom 1.8 million live in the capital Montevideo and its metropolitan area...
an coastline (though see above for possible relatives). Sexual size dimorphism seems to be more pronounced in A. brasiliensis, while A. alticeps females and males are often enough about the same size. Both sexes of the present species are usually found equally frequently; in A. alticeps females appear to outnumber males by far. Reproductive isolation
Reproductive isolation
The mechanisms of reproductive isolation or hybridization barriers are a collection of mechanisms, behaviors and physiological processes that prevent the members of two different species that cross or mate from producing offspring, or which ensure that any offspring that may be produced is not...
is ultimately achieved via behavior and genital anatomy
Anatomy
Anatomy is a branch of biology and medicine that is the consideration of the structure of living things. It is a general term that includes human anatomy, animal anatomy , and plant anatomy...
, but quite often inspecting the differently-sized and differently-smelling
Pheromone
A pheromone is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting outside the body of the secreting individual to impact the behavior of the receiving individual...
burrow entrance will already allow these spiders to identify conspecifics. In addition, the species also seem to have different microhabitat preferences.
Further reading
(2007): Daring females, devoted males, and reversed sexual size dimorphism in the sand-dwelling spider Allocosa brasiliensis (Araneae, Lycosidae). Behavioral Ecology and Sociobiology 62(1): 29-35. (HTML abstract and first page image) (in print): Male sexual cannibalism in a sand-dwelling wolf spider with sex role reversal. Biol. J. Linn. Soc., in print. (HTML abstract) (2010b): Sexual dimorphism in chelicerae, forelegs and palpal traits in two burrowing wolf spiders (Araneae: Lycosidae) with sex-role reversal. J. Nat. Hist.Journal of Natural History
The Journal of Natural History is a scientific journal published by Taylor & Francis focusing on entomology and zoology. The journal was established in 1841 under the name Annals and Magazine of Natural History and obtained its current title in 1967...
44(19-20): 1189-1202. (HTML abstract) (2011): Spatial distribution, burrow depth and temperature: implications for the sexual strategies in two Allocosa wolf spiders. Studies on Neotropical Fauna and Environment 46(2): 147–152.