by Paul Donovan
In last month’s edition of Herpetoculture Magazine, I covered the intricacies of scorpion reproduction. As the spider hobby is bigger than the scorpion one, and many keepers aspire to breed their animals, I thought it only pertinent to cover spider reproduction in a similar light.
Courtship and reproduction is as complex in spiders, as it is for scorpions and insects, and shares many similarities, none less-so than the male often being significantly smaller than the female, and the chance of being viewed as food, rather than a prospective mate, is high.
For a successful mating to take place, the male spider must give specific signals to the female. These signals form the basis of a number of functions:
a) To inform the female that he is of the same species.
b) To indicate his intention to mate.
c) To stimulate and arouse her so that she will, hopefully, co-operate.
Many of the courtship rituals undertaken by the male are complex and elaborate involving sound, movement, vibrations, pheromones etc. While these behavioural mechanisms are designed to suppress the females desire to eat him, some males resort to more brutal tactics. Crab spiders, for example, are ruthless lovers and seldom bother about preliminary courtship rituals – they simply jump onto the females back, and mate. Other spiders exhibit bondage tendencies. After ‘sweet-talking’ the female, the male ties her down with flimsy strands of silk. Although the silk is not strong enough to hold her down for any length of time, it does appear to induce a calming effect giving the male sufficient time to do his deed.I will come back to courtship in a moment, but let’s first look at the male and female reproductive organs.
Male Genitalia
Male spiders have two testes located in the abdomen which open to the surface via the epigastric furrow. The testes are organized in a complex tubular arrangement and produce the sperm cells needed for fertilisation. During the release of sperm from the body and taken up by the male into his palps, the sperm cells remain gathered together in small packets rendering them immobile. It is only once the packet is inside the female does the outer coating dissolve and the sperm cells become mobile.
Male spiders have no external genitalia with which to impregnate the female. Instead, they have a specialised organ called the embolus, located at the tips of the pedipalps – sometimes simply referred to as ‘palps’. This organ can vary in structure from a simple tube to a complex configuration. The male spins a sperm web, on which he deposits a globule of sperm. This is then sucked up by capillary action into the expandable emboli. When fully ‘charged’ the tips of the palps appear swollen, and bulbous, and the male is ready to mate. The sperm cells are stored inside ducts. However, it is unclear how the sperm is expelled, as there appears to be no increase in hemolymph pressure.
During mating, the male inserts his embolus into the female’s genital opening where it enters a coiled duct leading to the spermatheca. Here, the sperm is deposited, and remains until required for egg fertilisation. The emboli in many species can be quite long, sometimes exceeding the body length. During mating and the introduction of the palps into the female, the emboli may break off and remain inside the female. It appears that this occurs with regularity in species such as Widow Spiders in the Latrodectus genus. Why this should be is still unclear, but it does not suggest that neither sex can mate again, for they can. Males with damaged emboli are capable of fertilising females, just as females are capable of receiving sperm.
Female Genitalia
The females genitals are located within a fold of skin called the epigastric furrow. This is positioned at the front, on the underside of the opisthosoma resembling a slit, and leads to the egg producing ovaries. The ovaries are paired, elongated structures positioned ventrally in the abdomen with the oocytes projecting into the abdominal cavity. The number of eggs produced by a female can be truly massive. Female Salmon Pink Bird Eaters, Lasiodora parahybana, can produce up to 3000 eggs per sac; but these are also big spiders. The yolk within the egg sustains the developing embryo, not only during the development phase, but right up until the spider catches its first meal.
The epigyne or epigynum, is the female sex organ, and depending on the species, females can have a single opening used for both impregnation and egg laying or, three openings; two to accommodate the palps and a third for egg laying. The epigyne is quite a complex structure and has a direct relationship with the structure of the male’s embolus. The two can be comparable to a lock and key; the embolus is the key, and the epigyne the lock. This prevents sexes from different species mating with one another; although it is very unlikely that an unrelated species in the wild would get this far into the act anyway.
Females of most species have the ability to store sperm, meaning they can continue to produce viable eggs for some considerable time after being mated. However, as the spermatheca are shed along with the rest of the skin, a recently mated female will effectively become a “virgin” again, and have to be re-mate in order to produce viable eggs. Females will continuously produce eggs which, if unfertilised, will be reabsorbed into the body. However in some instances, unfertilised eggs may be laid, and the female guard the egg sac as though it were viable. These eggs will not hatch, and eventually she will eat them.
Attracting a Mate
The world is a big place for the spider, so techniques must be employed to attract a mate. One of these is the use of pheromones. Pheromones are widely used in the animal kingdom to bring the sexes together. In fact, it is the primary means of communication in many animal groups, such as snakes, and much reliance is placed upon it. With spiders, it is often accompanied by other signaling techniques. The individual strands of a female’s web, are overlaid with pheromones which triggers the male into specific courtship responses. These involve identifying himself to the female, and that he is interested in mating her.
Females of other species of spiders, in particular the Orb-webs of the Nephila genus, actively release pheromones into the air in order to advertise her presence to a male. However, it is believed that these pheromones can only be detected over very short distances of around a metre or so.
Unfortunately, these species-specific pheromones are short lived, but they do help the male avoid chasing the wrong species and potentially ending up being a meal. They also prevent him from wasting time pursuing a female who has abandoned her web. The release of pheromones by the female is an obvious stimulant for the male to seek her out and instigate mating. There is some evidence, showing that female Latrodectus can also detect pheromones males release onto their webs. Active hunting spiders such as Wolf spiders and Tarantulas, who do not construct webs in order to catch food, may lay down specialised trip-lines which they coat with pheromones or, release pheromones into the air to attract mates.
Web plucking
Web plucking is a typical courtship response by the male of web-spinning spiders. Once the male is sure he has detected the female of his species, he serenades her by plucking the web ‘strings’. Some of the best exponents of web plucking are the Orb-Weaver spiders Nephila and Argiope. However, two extremes can be seen here. While the male of some species pluck the web and then launch themselves towards the female, others are a little more reserved, enticing the female to come to them. The male attaches a short mating thread to the web and then begins plucking it. Interested female’s pickup these vibrations, and then move towards this thread. When she is on it, mating takes place.
Leg displays
Visual displays play an important role in courtship for many spider species. Two groups where this is displayed to the greatest effect, are the wolf spiders in the genus Lycosa and Jumping spiders of the Salticidae family. These spiders drum their palps on the ground and wave their legs in the air. This display is all the more spectacular in Salticidae, as they are some of the most colourful of all the spiders.
The legs of male Jumping spiders are much more robust than those of the female, and adorned with brightly coloured iridescent hairs. As the male waves his legs, the female responds by waving her legs or palps, and approaches the male. This response brings about an energetic dance by the male, and mating takes place when the female signals her willingness to mate by reaching out and touching him. It is a truly mesmerising spectacle to watch.
Leg displays are also practiced by tarantulas. When in proximity to a female, the male tarantula begins to tap the ground. The specific rhythm the male makes, signals to the female that he is not only of the same species, but is in breeding condition. These tapping sounds are audible to the human ear.
Gifts
Coercing a female into mating with the allure of a gift, is not uncommon in the spider world. One spider known to use this technique, is the male European Nursery-Web spider, Pisaura mirabilis. Once his interest has been stimulated by pheromones on drag-lines let out by the female, he jumps on the first insect which happens to pass by. Swathing it in silk, he holds the insect aloft in his fangs as he goes in search of a female. A receptive female accepts the gift by grabbing it with her fangs, during which time the male darts beneath her and mates her.
Rape
Spider courtship can sometimes be brutal. The European spider, Drassodes lapidosus, actually resorts to raping females. A sexually mature male will go in search of an immature female, and then snuggles down besides her. As soon as she undergoes her final moult he pounces and mates her. As her new exoskeleton is still soft, she is unable to move and defend herself.
Fang Disablement
Before the male has a chance to mate, he must first disable the female’s fangs. I touched on how the male European Nursery-Web spider does this by offering the female a gift. The gift is not so much a love token, but a way of immobilising her ability to kill him. Tarantulas use a slightly different approach.
As the male tarantula has his last moult, signifying he has become sexually mature, he develops a spur on the tibia; called, rather unsurprisingly the ‘tibial spur’. Following a period of pre-courtship leg tapping, the male tentatively approaches the female. In one attempt, he must hook the female’s fangs in these spurs, thus immobilising them. If he misses, he could end up as her next meal. When secure, he pushes her upwards and backwards to expose her epigynum, inserts his swollen palps and the transfer of sperm takes place. The male inserts his palps one at a time, though each may be inserted several times. Mating can last from a few minutes to several hours.
Not always eaten
It has been a long standing belief that female spiders always eat the male after mating. This is not the case. Following the transfer of sperm, the male makes a hasty retreat from within the proximity of the female. The real danger to the male, comes during the courtship ritual when the female may fail to recognise his mating signals. Given the chance, a male will mate with as many females as possible to spread his gene pool. Although the female Black Widow may get her name from the habit of eating her partner, even he sometimes escapes.
Most instances of males being eaten are reported from captive observations, where the confines of the cages hinder his escape. I have witnessed countless matings of numerous spider species in the wild, and in almost all cases, the male escaped to mate another day.
There are, of course, examples where the male willingly sacrifices himself. Male Araneus pallidus appear only to be able to insert his palps into the female if she is holding him in her fangs. This sacrificial act may appear rather strange at first, but it does give the female a post-mating meal, thus ensuring she is in a healthy state for egg production.
Egg Sacs
The period from mating to egg laying varies enormously through the spider genus. It can occur within a couple of weeks, or extend anywhere up to eight to ten months. Factors determining this are largely relevant to temperature, humidity, food availability, etc. Fertilisation occurs just before the eggs are laid with the stored sperm uniting with the eggs as they pass through the uterus externus. The eggs emerge from the genital opening coated in a gooey liquid which gradually dries, sticking the eggs together.
The eggs are protected in a silken cocoon. The cocoon not only provides a protective coating for the eggs, but insulates them against temperature fluctuations and protects them from predators. The cocoon is constructed from tight criss-crossing of fibres which gives the outer coating its toughness. In a number of species, notably Avicularia spp, and Theraphosa, urticating hairs may be woven into the cocoon to increase its protection against predators.
With so many spider families it is inevitable that the construction of a cocoon does not follow the same blueprint. For example female Daddy Long-Legs of the Pholcus genus, simply wrap their eggs in a few strands of silk and then carries them in her chelicerae; Latrodectus form small spiky-golf ball egg sacs the size of a pea; and the African Two-tailed spider Hersilia, stick their eggs to tree trunks with a silken blanket, and then camouflage it with loose tree bark. Some species, such as Wolf spiders and Huntsman spiders even carry their cocoon around, either in the fangs or attached to the spinnerets.
When due to hatch, the female may use her fangs to tear the egg-sac in order to allow the young to escape. The spiderlings may then disperse over the ground, throughout the web or climb onto the females back where they hold onto special hairs. Here they will remain for a few days before dropping off and making their own way in life.
As with the Wolf spiders, the female Nursery Web spider, Euprosthenops, found in Southern Africa carries her egg-sac around with her. Just before the spiderlings are ready to emerge, she fastens a number of twigs or leaves together with silk, and then deposits the egg sac within this before encasing it in silk. This structure is designed to protect the spiderlings until the first or second instar stage. When large enough, the spiderlings ‘bite’ their way free and disperse. At all times, they are guarded by the female.
As a rule, although it is a very broad rule, spiderlings from arboreal species tend to be larger than those from terrestrial species. The reason for this could be due to the diversity of prey availability. On the ground there is a more widespread array of small prey available, than there is in an arboreal setting. These arboreal species may also have to deal with proportionally larger prey.
Double clutches
As with scorpions, a number of tarantula species can produce several clutches from a single mating; what is commonly referred to as “double clutching”. A quantity of sperm may be used to fertilise a clutch, and the remainder used sometime later to fertilise a second clutch within a single moult cycle. The period between the first and second clutch, can extend from a couple of weeks, to several months, with each clutch being of similar size.
There are many factors influencing double clutching, such as environmental conditions; egg quality; sperm quality and egg survivability, but it is not known how widespread the behaviour is or, whether it occurs throughout all spider genera, or just in some. Some species it has been documented in include Psalmopoeus spp, Poecilotheria spp, Hysterocrates spp, and Ephebopus spp.
Parthenogenesis
Parthenogenesis is a widely adopted method of reproduction in the invertebrate world, whereby a female can produce young without the intervention of a male. Although parthenogenesis is not widespread amongst arachnids, it does occur in several genera, including Dysdera, Theotima, and Triaeris. Many isolated females of this species have produced viable eggs without the intervention of a male. Not only were egg sacs laid but, female spiderlings became sexually mature and were themselves able to reproduce without a male.
Tail–end
Spider reproduction is a highly complex behaviour, encompassing a multitude of different behavioural techniques. If one of your spiders turns out to be a male, buy a female and try breeding them. You have nothing to lose, and the satisfaction you get from watching an amazing spectacle unfold, will be worth all the anxiety.
