The Andalusian Funnel-Web Spider – Macrothele calpeiana
Hidden beneath stones, tree roots and the leaf litter of southern Iberia lives one of Europe’s most impressive spiders. Macrothele calpeiana, commonly called the Andalusian, Spanish or Gibraltar funnel-web spider, is a large, dark mygalomorph spider whose striking appearance has inevitably earned it a rather fearsome reputation.
In Spain it is also known as la araña negra de los alcornocales — the black spider of the cork-oak forests — a particularly appropriate name in Andalucía, where some of its best-known populations occur among the extensive cork-oak woodlands of Cádiz and Málaga.
Despite its appearance, Macrothele calpeiana is an elusive animal. It spends much of its life concealed inside an elaborate silk retreat and is far more likely to be detected by its distinctive web than by seeing the spider itself.
How to identify Macrothele calpeiana
This is a substantial spider by European standards. Adult females can reach approximately 35 mm in body length, with males generally somewhat smaller. Including the legs, a large individual can appear considerably bigger.
Living specimens are very dark, usually appearing glossy black, while the abdomen may show subtle violet or purplish tones. Fine hairs cover the abdomen and legs.
One feature, however, is particularly distinctive: the spider’s very long posterior spinnerets.
These project conspicuously from the rear of the abdomen and can almost give the impression of an additional pair of short legs. They are one of the most useful characteristics for distinguishing Macrothele calpeiana from superficially similar spiders.
The spider is sometimes mistaken for the Mediterranean trapdoor spider Amblyocarenum walckenaeri. Their lifestyles and appearance have similarities, but the prominent elongated spinnerets of Macrothele provide a useful identification clue.
A spider that advertises its hiding place
Finding the spider itself can be difficult. Finding its home is considerably easier.
Macrothele calpeiana constructs a conspicuous sheet of silk across the ground or another suitable surface. This sheet narrows towards a funnel-shaped entrance leading into a protected tubular retreat.
Webs can occur beneath rocks and fallen timber, around tree roots, on shaded banks and among vegetation. Stone walls, cracks and natural cavities can also provide suitable locations.
Remarkably, the spider does not always live at ground level. Retreats have occasionally been found in hollows and crevices in trees above the ground.
The silk acts as more than simply a shelter. It is effectively an extension of the spider’s senses.
An insect moving across the sheet creates vibrations which travel through the web. Waiting within its retreat, the spider detects these movements and can rapidly emerge to seize the unfortunate visitor.
Life underground
The funnel leads backwards into a sheltered tube, often extending into soil or an existing cavity.
This retreat provides the spider with something particularly valuable in the hot Mediterranean climate: a relatively stable microclimate.
Conditions deeper inside can remain cooler and more humid than those outside. This helps explain the spider’s preference for sheltered environments with shade, moisture and suitable places in which to construct its retreat.
Cork-oak woodland provides excellent conditions.
The enormous Los Alcornocales Natural Park in Cádiz is especially associated with the species. Its extensive Quercus suber forests, shaded ground and deep accumulation of organic material provide numerous suitable microhabitats.
However, Macrothele calpeiana is not restricted to pristine cork forest. It has also been recorded in scrub, pine and eucalyptus habitats and even some human-modified environments where suitable shelter and microclimatic conditions exist.
A nocturnal ambush hunter
During daylight hours the spider normally remains safely inside its retreat.
Activity increases after dark.
Rather than roaming extensively in search of food, the spider usually allows its web to do much of the work. Beetles, woodlice, millipedes and other arthropods crossing the silk produce vibrations that alert the waiting predator.
The spider emerges rapidly, captures the prey with its chelicerae and delivers venom through its fangs before retreating with its meal.
Like other spiders, it uses digestive fluids to break down tissues before consuming them.
The remains are subsequently removed from the retreat. Macrothele calpeiana also spends considerable periods grooming its body and legs, behaviour that may help remove debris and reduce external parasites such as mites.
Where does the Andalusian funnel-web spider live?
The natural distribution of Macrothele calpeiana is centred on the south-western Iberian Peninsula, with particularly important populations in southern Spain.
Cádiz contains the greatest concentration of known Spanish records, followed by Málaga, although the species occurs more widely.
Recent research has significantly improved our understanding of its distribution. A major study compiling historical observations, scientific records and citizen-science reports mapped the species across 156 10 × 10 km survey squares, representing roughly 2.7% of the Iberian Peninsula.
Cádiz and Málaga accounted for the majority of documented localities, with important concentrations associated with protected landscapes including Los Alcornocales, Sierra de Grazalema and Sierra de las Nieves.
The species is also native to Portugal, where recent surveys have added considerably to knowledge of its ecology and distribution. Portuguese populations appear patchily distributed across suitable terrain in the south and south-west, with cork-oak woodland, heathland and suitable roadside banks among the habitats used.
Its accepted wider range also includes Morocco and Algeria.
An accidental traveller
Curiously for a spider that normally spends much of its life inside a burrow, Macrothele calpeiana has become an accidental international traveller.
The trade in mature ornamental trees — particularly old olive trees transported with large root balls — provides one explanation.
A spider concealed among roots or soil can effectively be transported together with its entire refuge.
Records have consequently appeared well beyond the species’ normal Iberian range. Recent research documents non-native observations from eight European countries, with repeated reports particularly from France and Italy.
That does not necessarily mean permanent populations become established wherever individuals are discovered. Climatic conditions, especially colder winters in central and northern Europe, may prevent transported spiders from forming sustainable populations.
Courtship and reproduction
For much of the year females remain closely associated with their retreats. Adult males become much more mobile during the breeding season, with much of their wandering activity recorded during spring.
For a male, approaching an adult female’s web requires a little diplomacy.
Instead of behaving like prey, he must communicate his intentions through movements and vibrations transmitted through the silk.
Following mating, the female eventually produces an egg sac and remains closely associated with it. The protected burrow allows her to move within the retreat in response to changing temperature and humidity.
When the spiderlings emerge they initially remain around their mother’s web before eventually dispersing and constructing retreats of their own.
For an animal often portrayed simply as an intimidating predator, the extended association between female, egg sac and young reveals a considerably more complex life history.
Is Macrothele calpeiana dangerous?
Its glossy black body, large fangs and defensive posture certainly make Macrothele calpeiana look formidable.
When seriously disturbed it can raise the front of its body and expose its chelicerae. The sensible response is simply to leave it alone.
It should not, however, be confused with the medically significant Australian funnel-web spiders. Sharing the term “funnel-web” describes aspects of their web-building behaviour; it does not mean that the European species presents the same danger to people.
As with any large spider capable of biting, Macrothele calpeiana should not be handled.
In normal circumstances there is little reason for a person and spider to come into conflict. The animal spends most of its time concealed and is principally active at night.
A protected European spider
Perhaps the most remarkable fact about Macrothele calpeiana has nothing to do with its size.
It has the unusual distinction of being the only spider species currently protected specifically under European Union legislation.
It is included under Annex IV of the EU Habitats Directive and is also covered by the Bern Convention. Its restricted natural distribution, fragmented populations and significant genetic differences between some populations contribute to its conservation importance.
Recent research also demonstrates how useful public observations can be in understanding such an elusive animal. Citizen records have identified previously undocumented areas and substantially improved knowledge of its European distribution.
Seeing one in the wild
Despite its size, visitors to Andalucía are unlikely to encounter Macrothele calpeiana wandering around during the day.
The web is what to look for.
A broad, slightly untidy sheet of white silk disappearing into a funnel beneath a rock, root or bank may indicate that a spider is hidden inside.
If you find one, there is no need to disturb it or lift the surrounding stones. Apart from protecting the spider, leaving the site untouched preserves the carefully constructed retreat and the cool, humid conditions on which its occupant depends.
After sunset, patience may occasionally reveal the owner sitting close to the funnel entrance, waiting for vibrations across the silk.
It is an impressive sight: a large black spider almost perfectly adapted to a hidden existence beneath the cork-oak forests of southern Iberia.
And for an animal that spends most of its life underground, Macrothele calpeiana has turned out to be one of Europe’s most fascinating spiders.