Captive breeding of the funnel web spider,Macrothele calpeiana

Captive breeding of the funnel web spider,Macrothele calpeiana by Luke Perry

Introduction : As the only European representative of the Mygalomorph family Hexathelidae, the Gibraltar Funnelweb Spider has been the subject of some interest amongst Tarantula keepers in the UK (Hancock & Hancock, 1992; Gallon, 1994; Perry & Luing 2002), although limited work has been carried out on captive breeding to date. Whilst locally abundant in areas of cork oak and pine forests, as well as in citrus groves, Macrothele calpeiana is very restricted in its' distribution to mainly Gibraltar and the nearby range of hills which stretch just 100km from Tarifa to Ronda in Southern Andalucía, Spain (Blasco & Ferrández, 1986; Snazell & Allison, 1989; Santos Lobatón, 1996, Ferrández, Fernández de Céspides & Perucho, 1998). Consequently, it is now protected by the EU Habitats Directive (Helsdingen & Decae, 1992) and although new data points towards small but isolated populations elsewhere (Díaz Rodríguez & García-Villanueva, 2000), captive breeding still represents an important initiative to promote better understanding of the behaviour and life-cycle of this impressive spider and minimise the need for its' collection in the wild.

Description : M. calpeiana is considered to be Europe's largest spider, with a body length of up to 3.5cm and a leg span reaching 8cm. Its' carapace and legs are glossy black in appearance, with the abdomen coloration varying from a uniform velvety black to purple/violet with a marked cardiac line, depending upon the moult stage and nutritional state. Flexible finger-like spinnerets up to 1.5cm in length make this spider unmistakable. Its' home consists of a retreat tube, constructed in a suitable enclosed space, extending outwards to form a sheet-like capture web which is firmly attached to surrounding stones, roots or twigs with strong silken struts, covering an area of around 150-300cm²(sometimes more, as neighbouring webs can be contiguous if ground cover is limited).

Habitat Requirements : With distribution limited to a small geographic area characterised by hot summers, warm winters, relatively high rainfall and a localised moist easterly wind known as the Levanter, understanding of temperature and humidity requirements is essential for the maintenance of M. calpeiana in captivity. As can be seen in table 1, temperature varies significantly throughout the year and will undoubtedly be linked closely to some of the key events in the spider's life, such as egg-sac production. Rainfall also shows some considerable variation with distinct wet and dry seasons. Despite this, humidity averages 65% at midday, increasing to around 85% at night all year round. The silken retreat of M. calpeiana, typically constructed in a scrape under a rock, amongst tree roots or in the gaps of dry stone walls, often extends into a burrow in excess of 50cm deep and plays an important role in regulating temperature and humidity. At midday in summer, temperature within the retreat is usually 3-5°C lower and humidity 20-25% higher than prevailing external conditions. Distribution of larger populations of this spider also corresponds with lower elevations, approximately 50-200m above sea level. This probably reflects a moisture gradient in the soil, as indicated by the increased amount of ground cover from various plants, bushes and trees at this level.

Sex Determination : Sexing can be positive from the sixth moult onwards using x30 magnification, although the exuviae should be viewed against a dark background with angled, overhead lighting as the sexual organs are transparent. The female has paired elongate spermathecae, coiled into twin spirals, but which may unfurl when the abdomen skin is soaked. The internal view of the male's genital area is unremarkable, with just a tiny gonopore present and no obvious accessory organs. Both sexes have interesting slit sensilla and arthordial membranes. Externally, the female epigynum area is sclerotised throughout, whilst the male is only lightly and partially so with the amount of sclerotisation decreasing anteriorly. Sexing is therefore possible in larger specimens by examining the ventral surface with a hand lens, but this method is not so reliable with juveniles. In adults, size alone can be used to differentiate the sexes, with body length in the slender male being approximately two-thirds that of the female, although leg span is similar. The male palpal bulb is simple in form, with a very long straight tapering embolus. Tibial spurs are absent.

Mating : Subadult males undergo their final moult in the late autumn but it is not until the spring, with the onset of more clement weather that they commence actively seeking a receptive female. Between March and May, males can easily be located after dusk outside of their webs, wandering the vicinity. It is believed the female is located through detection of pheromones present within her silk. The male entices her out of her retreat by plucking at trip lines at the edge of her capture web with his palps and by shaking his entire body very slightly and only briefly, pausing and then repeating this action. He must be very cautious, as the female usually responds to any vibration information in her capture web aggressively. To avoid having his presence misinterpreted as a meal, the male continues his courtship signals and is also very likely stridulating subaudibly throughout, by opposing stout spines on the posterior face of the palpal trochanter against a dense patch of highly modified paddle-shaped spines on the anterior surface of the coxa on leg 1. Not exactly flowers and chocolates, but for the receptive female it is irresistible!

Once she emerges, he begins to approach with both pedipalps raised, whereupon she rears up into a defensive posture, baring her fangs and rapidly moves her own palps up and down alternately, making a clearly audible hiss with her stridulatory organs. On initial contact, the male strikes her with legs 1 and 2 after which a period of wrestling ensues as the male attempts to push her back further into an arched position. Once this goal is achieved, the female typically becomes quiescent and the male then proceeds to tap under her sternal plate briefly, before reaching for her epigynum with his palps. As the embolus is long and inflexible, he has to reach well beyond her epigynum and rotate his palp outwards through a 90° angle to bring it into a position where it can be inserted. After a sharp backward tug to discharge his sperm, he repeats the process with the other palp. In approximately 75% of observed pairings, the male inserts his emboli repeatedly, with each insertion lasting 30-60 seconds and the average mating lasting ten minutes. This period is interspersed with breaks lasting a couple of minutes, during which the male slides out from under the female but maintains touch contact with her using legs 1 and 2. Whilst in this position, he cleans each palp and embolus with his mouthparts - this action seems to straighten out his emboli which may have been bent during contact with the hard sclerotised female epigynum. During these breaks, the female can be observed to lay down silk, moving her abdomen and spinnerets in a side to side motion. Mating is initiated again by the male tapping his palps on the web surface and she responds with the same flurry of palp movements seen previously. Following successful mating, the male typically disengages first and beats a hasty exit. Occasionally he may be attacked and killed, but more often he is not pursued as the female either remains motionless or returns promptly to her retreat.

Captive breeding is made difficult by the fact that the female will rapidly fill any container with layer after layer of dense webbing, with multiple convergent retreat tubes. A male cannot be safely introduced directly into this without causing significant movement of the web and he will most likely be attacked before he can initiate courtship signals. Moving the female into a new container a few days beforehand appears to remedy this problem. She has time to lay down some silk and form a retreat, but does not have the opportunity to make an extensive web structure. After ensuring the male has charged his palps (sperm web production can be artificially triggered by placing a small piece of her silk in his container), he should be enticed into a camera film pot and this can then be placed at the very edge of her capture web during the day, providing him with a temporary artificial retreat. He is unlikely to leave this until darkness falls, which allows him to make the necessary advances at his own pace. Even with these precautions, there are no guarantees. Sometimes the male will meet his demise anyway but very occasionally, he will attack and kill his intended mate.

One interesting observation is that following successful breeding, the male can often be left to cohabit with the female in her web. This has been recorded for not only M. calpeiana, but also other closely related funnelwebs (Simon-Brunet, 1994) both in the wild and in captivity. Why this should occur in what are otherwise non-social spiders is unclear. However, as the male can often be seen to add his own silk to the females web, it is possible that he is creating confusing chemical signals for other potential suitors, thus ensuring his paternity of the offspring. Whatever the reason for choosing to stay rather than attempting to locate another receptive female, one thing is clear - this is a risky strategy. His body is often found outside of the retreat a few days or weeks later, having been dispatched with a bite through the cephalothorax.

Egg-Sac Production : Over the following weeks, very few prey items are declined by the female. In July, she seals herself into her retreat to produce her egg-sac, which measures 1-1.5cm in diameter. She carries this in her palps through most of the incubation period, turning it at frequent intervals. Temperature of the developing young is probably regulated in the wild by the female moving the egg-sac up or down her burrow at different times of the day, whilst in captivity, she can often be seen suspending it in her web near to the heat source. After four to five weeks of guarding the egg-sac, intensified movement from within following the spiderlings' first moult probably triggers the female into making a small hole in its' surface with her fangs and her offspring begin to emerge. Data from captive breeding is presented below and it can be seen that brood size is quite variable.



Rearing of Spiderlings : Emergence of offspring coincides with a period of extended drought and high temperatures. It is very difficult to locate any spiderlings outside of the maternal retreat throughout August and September and it is likely they remain with her until the rains commence in October, taking small prey items from her capture web in the meantime. One reason for this may be that M. calpeiana does not possess a digging rastellum and consequently would be unable to excavate a burrow in the dry baked soil, leaving spiderlings vulnerable to excessive heat, low humidity and easy predation. As large numbers of offspring are produced, this makes for a very crowded burrow and after a couple of moults, dispersal is eventually triggered by lack of space, onset of cannibalism and seasonal change in external conditions. In captivity, this means that separation is not an immediate need and spiderlings can be left together until the third moult as long as adequate nutrition is provided. Microcrickets are readily taken, but group feeding can also be observed with larger prey items which have been discarded by the mother. Given the small size of spiderlings and relatively slow growth rate, separation is initially into 30ml containers, increasing to 90ml at four months and 250ml at six. By one year, transfer to 500ml jars becomes necessary to accommodate increased size and extensive webbing. Larger juveniles are housed in plastic containers measuring 30x18x12cm to give adequate space for the capture web. A cork oak bark shelter should be provided, with peat or coconut fibre being a suitable medium for burrowing and web anchorage. Moisture requirements are met by lightly spraying one end of the container on a weekly basis and providing a night time drop in temperature to allow dew to form. Variation in diet is probably important, given that M. calpeiana is an opportunistic feeder and takes advantage of whatever prey is locally abundant. Analysis of web contents has revealed the remains of millipedes, beetles, weevils, caterpillars, bees, earwigs, ants, flies and even snails. These can be supplemented in captivity with crickets, mealworms and locusts, along with other insects found around the home.

Growth Rates : On emerging from the egg-sac, spiderlings have a leg span of just 3-4mm. After six moults over increasing intervals in the first twelve months, they eventually attain an average leg span of 3.5cm. Captive bred males mature at 15-18 months, after a further two moults, although data from other related genera (e.g. Atrax and Hadronyche) seem to suggest this may take longer in the wild (Scott, 1980), given that food availability is more variable that it would be in any captive breeding programme. Male life expectancy is limited to an average of six months (range 2-10 months) following the final moult. Females by comparison take 4-5 years to mature, moulting twice in their second year and annually thereafter. They can live for several more years, producing a new brood of offspring in every year of their adult lives.

Conclusion : This active spider is interesting to observe at all stages of its' life. It makes a good addition to any collection and is quite easy to maintain in captivity. The survival rate of offspring is good, provided habitat requirements are fully considered.






References

Scott, G. (1980)
'The Funnelweb'
Darling Downs Institute Press, Toowoomba



Blasco, A. & Ferrández, M.A. (1986)
'El género Macrothele Ausserer 1871 (Araneae : Dipluridae) en la Península Ibérica'
Actas X Congr. Int. Aracnol. Jaca/España.1:311-320

Snazell, R. & Allison. R. (1989)
'The genus Macrothele Ausserer (Aranaea : Hexathelidae) in Europe'
Bulletin of the British Arachnological Society, 8(3), 65-72

Hancock, K. & Hancock, J. (1992)
'Tarantulas : Keeping and Breeding Arachnids in Captivity'
R&A Publishing Ltd, Taunton

Helsdingen, P.J. Van, & Decae, A. (1992)
'Ecology, distribution and vulnerability of Macrothele calpeiana (Walckenaer)'
Tijdschrift voor Entomologie, 135 : 169-178

Gallon, R.C. (1994)
'Observations on Macrothele calpeiana (Walckenaer, 1805) in Southern Iberia'
Journal of the British Tarantula Society Study Group, (1):1-12

Simon-Brunet, B. (1994)
'The Silken Web : A Natural History of Australian Spiders'
Reed Books, Sydney

Santos-Lobatón, M.C. (1996)
'Estudio sobre Macrothele calpeiana Walckenaer 1805 (Araneae, Hexathelidae) en dos pinares de la provincia de Cádiz (España)
Aracnología 24:1-10

Ferrandez, M.A., Fernandez de Cespides, H. & Perucho, A. (1998)
'Macrothele calpeiana, la araña negra de los alcornocales'
Quercus, 1998 ABR; (146) 14-19

Díaz Rodríguez, E. & García-Villanueva, V. (2000)
'Primeros datos sobre la presencia de Macrothele calpeiana (Walckenaer, 1805) en Extremadura, España'
Revista Ibérica de Aracnología, Vol 1, 57-58

Perry, L. & Luing, M. (2002)
'Come into my parlour : a look inside the home of Gibraltar's Funnelweb Spider'
Journal of the Gibraltar Ornithological and Natural History Society, Occasional Paper No 1 (April)






Acknowledgements : Warm thanks are extended to John Cortés, Terence Ocaña and Eric Shaw of the Gibraltar Ornithological and Natural History Society for their interest in this study; Malcolm Luing for his practical assistance on numerous collecting trips; Belinda Gonzalez and family for their friendship, hospitality and local knowledge; John Stanney & Chris Felton of the British Arachnological Society library and Antonio Melic of the Grupo Ibérico de Aracnología for providing reprints of previous research papers; Guy Tansley for his generous help in photographing sex organs; finally to John Hancock* and Richard Gallon of the British Tarantula Society for sharing their observations, data and great enthusiasm for this spider. Macrothele calpeiana is now included in the BTS National Collection Scheme, the purpose of which is to maintain a viable captive breeding programme without further need to deplete wild populations and to promote research.



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