British Tarantula Society Study Group

Observations on Macrothele calpeiana (Walckenaer, 1805) in southern Iberia

By Richard C Gallon

1. Introduction

Macrothele calpeiana belongs to the family Hexathelidae, the funnel webs (Fig. 1). This spider is known to occur in southern Spain (Hancock 1992). During a holiday in southern Spain the opportunity arose to undertake a study of this species in its native habitat. The aim of the study was to gain an insight into the autecology of this most interesting of spiders.

The field study was undertaken principally near the town of Alhaurin el Grande, Andalucia, southern Spain between 23rd July and 5th August 1994. The study area lies at an altitude of 290 metres above sea level. During the same period casual observations were made at other localities in the region. A locality plan showing areas mentioned in this paper is appended with this report as Fig. 6.

The findings are recorded under three general sub-headings: -

•Habitat / Site description
•Behaviour
•Nutrition, Competition & Predation

Figure 1: Macrothele calpeiana

2. Habitat / Site description

The natural vegetation of the study area was found too be pine woodland and Mediterranean scrub. These sites at the study site at Alhaurin el Grande were not utilised by M. calpeiana. However the study site was located on a nearby citrus/avocado grove, a habitat strongly favoured by the spiders. The study transect was mapped by tape measure and compass and a metre quadrat employed for detailed examination.

The loam bank transect (Figs. 2 & 3) had practically no live floral ground cover. A three-cm layer of leaf litter covered the area below the cherry/avocado canopy. Where this canopy was broken the bare loam had a light scattering of vegetal detritus predominantly consisting of leaf litter and stem material. The flat citrus/avocado grove which was situated below the transect was heavily cultivated loam with no live floral ground cover. This area was devoid of M. calpeiana with the exception of a few juvenile webs seen anchored against the base of tree trunks. This area is kept free of ground cover by rotavator, which must deter or destroy any potential colonisers.

Figure 2: A three dimentional view of the transect (not to scale)

Figure 3: The transect area showing the position of specimens and other features

Records of the microclimate at the site were made using a thermometer and humidity gauge. The instruments were situated beneath a small plant on the soil surface. The climatic measurements thus recorded are shown graphically in Fig. 4 from which it is clear that as temperature increased during the day, humidity decreased and vice-versa following nightfall.

Figure 4: A comparison of temperature and humidity over 16 hours at the transect site (27th July 1994)

The transect area was close to 68 square metres and contained 44 juvenile and 96 adult/sub adult webs giving a density of 2.06 hexathelids per square metre (Fig. 3). It is estimated that the entire colony consisted of approximately 1500 members.

M. calpeiana was also found in the Montes de Malaga in mixed pine, cork oak and Kermes oak woodland, at Refugio de Juanar in the Sierra Blanca in pinewood and the botanical gardens of Gibraltar. These areas appeared much damper than the uninhabited pinewood at Alhaurin el Grande.

3. Behaviour

In its typical habitat this species inhabits a burrow excavated in the earth. The lower part of the burrow is unsi1ked and ridged in texture. In the upper portion of the burrow non-sticky silk is used to line the sides. This silk extends outside the burrow and is attached to nearby objects to form a simple labyrinth with two, three or possibly four entrances (Fig. 5). During the day a very light cover of silk consisting of but a few strands was seen over the entrances.

Figure 5: A burrow cross-section

Specimens adjacent to large rocks use the rock as part of the burrow wall. A specimen observed in the Montes de Malaga had a simple maze burrow rather than the usual mono-burrow.

At tree trunk sites the web is attached to the trunk and it is likely that the burrow utilises a tree root as a burrow side. In areas where such anchorage points are unavailable or have been brushed aside naturally, a funnel web with a single entrance is constructed. The morphology of the web is similar to that made by the Segestriidae spiders but without trigger lines.

The webs observed often have fragments of dead plant material incorporated ill them. Photographic evidence suggests that material falls on to the web and is just silked in. There is no evidence that the spiders deliberately incorporate the fragments into their webs.

M. calpeiana is to a lesser degree arboreal. In the Gibraltar Botanic Gardens three webs were seen two metres up in a palm tree trunk amongst frond stubs. A moribund cork oak (Quercus suber) at Alhaurin el Grande revealed a specimen again two metres up, but this time inhabiting the space between the bank and live tree this space was filled with rotten wood powder, which the spider utilised as a burrow medium.

Refugio de Juanar (altitude 780 m) also had an arboreal M. calpeiana some 0.20 metres from the ground in the fork of an olive tree. The largest web covered an area of 212 square centimetres and was seen at Refugio de Juanar.

The spiders vacated their burrows almost exclusively at night thereby avoiding daytime predators, excessive temperatures and times of low humidity. However Refugio de Juanar had two spiders active at 13h00 (1 Aug. 1994) in moderate shade. Most M. calpeiana stay on their webs at night but a few were seen on surrounding soil usually darting back when disturbed (torch light did not perturb the spiders). Almost all adults sport a colony of parasitic white mites on their carapace. One heavily parasitised individual was seen at night far from any web. On provocation this individual showed virtually no reaction, and moved only a few centimetres when disturbed a second time. Could this deviant behaviour be a parasite removal strategy? This individual could easily have been preyed upon effectively eliminating a heavily parasitised individual from the colony and thereby reducing the chance of infecting others in the colony.

At the end of July females were found with egg sacs and young. The sacs were white spherical and about 1 cm in diameter. These were carried around by the females. During excavation of two burrows it was noted that during the day the females clutching egg sacs, were high up in their burrows almost to the labyrinth of webbing. Was this an incubation activity? At one site the burrow was totally excavated; here the female clutching the egg sac was seen to pull it with her down the burrow as excavation proceeded. The egg sac formed a tight plug in the burrow. This female was particularly aggressive when collected perhaps as a result of loosing the egg sac down the hole?

On returning to the same site later it was noted that ants were carrying away the spider "larva". It is suggested that the heavy silking of the upper burrow may act as a deterrent inhibiting any ant predation. Several spiderlings were seen at night at the web entrance to a burrow accompanying their mother. When the mother was disturbed the spiderlings darted back down the burrow after their parent. This poses the question as to whether the spiderlings were hunting from the female’s web?

4. Nutrition, Competition and Predation

4.1 Nutrition

The following is a list of nocturnal invertebrates found in the vicinity of the transect. All could be prey for M. calpeiana. However it is less likely that the ant lion and cicada form an important part of the diet as they are less terrestrial than others on the list.

Order

Family

Species

Name

Size (mm)

Size (mm)

Hymenoptera

-

-

Ant species 1

12 soldier

7 worker

Hymenoptera

-

-

Ant species 2

3 soldier

2 worker

Neuroptera

-

-

Ant lion

25

-

Orthoptera

Gryllidae

Gryllomorpha dalmatina

Cricket

9

-

Coeleoptera

-

-

Stag beetle

15

-

Coeleoptera

-

Scatophagus

Beetle

19

 

Embioptera

-

-

Web spinner

-

-

Hemiptera

Cicadidae

Cicada orni

Cicada

-

-

Isopoda

-

-

Pill woodlouse

12

-

Isopoda

-

-

Woodlouse

12

-

Chilopoda

-

Scutigera sp.

Centipede

-

-

Arachnidae

Pholcidae

-

-

-

-

Arachnidae

Lycosidae

-

Wolf spider

Large

-

The web spinner and pholcid seldom appeared too leave their webs and are therefore unlikely prey. On the other hand Scutigera sp. and the lycosid are formidable predators and would be a match for M. calpeiana.

Evidence of the diet of M. calpeiana was gained from the examination of insect remains on the webs and dissection of web detritus in the laboratory.

On site a large adult female, (about 30mm) had within her web: -

•A moult and fragments of previous moults.
•Fragments of a queen wasp.
•Fragments of a queen bumble bee.
•Remains of a large black scatophagus beetle
•Remains of a devil’s coach horse beetle.

The wasp and bee may have been caught whilst attempting to find a hole in which to hibernate.
The webs of two smaller M. calpeiana, like the previous specimen from Alhaurin el Grande contained: -

•Moults and fragments of previous moults
•The elytra of three beetle species
•A silk wrapped uneaten assassin bug
•Fragments of two species of woodlouse
•A few uneaten ants.
•The head of a caterpillar.
•Live mites and a psocid were also found. It is apparent that the spiders obtain drinking water from the dew, which forms on the webs during the earlier hours of the morning.

4.2 Competition

As far as food competitors are concerned, Scutigera and the lycosid would consume similar prey to Macrothele. A phlocid spider was seen to have constructed its web above that of a M. calpeiana. This phlocid would thus intercept airborne prey destined for the funnel web.

4.3 Predators

Potential predators for M. calpeiana could include the disc-fingered gecko Hemidactylis turcicus, Scutigera, the large lycosid, Empusa pennata (mantid) and hunting wasps. During the day a Blackbird, Turdus merula, was seen working the leaf litter for food and so may be a predator to stray individuals.

5. Conclusions

•Macrothele calpeiana occurs in damp shady localities in southern Spain.
•It is chiefly nocturnal, leaving its burrow two after sunset.
•It inhabits a burrow with a simple web labyrinth at the top, which is anchored to surrounding objects.
•Plant material within the web falls or is blown on to the web and silked in rather than being deliberately incorporated in the web.
•M. calpeiana is partially arboreal, although predominantly terrestrial.
•There may be a behavioural strategy for controlling mite infestation within the colony.
•Females are with egg sacs and spiderlings at the end of July.
•Its diet includes isopods, hymenoptera, coleoptera plus others.
•Potential competitors and predators are recognised.

6. Acknowledgement

Thanks are due to K. & J. Hancock for providing the species author.

7. References

HANCOCK, K. & J. 1992. Tarantulas: Keeping and Breeding Arachnids in Captivity, R+A Publishing Limited, Taunton, England.

Figure 6: The locality map showing areas mentioned in the study

This is the online version of: -

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

First published September 1994.