The world of arachnids is diverse and fascinating, with species adapting to a wide range of environments. Among these are the cave-dwelling spiders, which have evolved unique characteristics to thrive in the dark, often harsh conditions of subterranean habitats. This article delves into the intriguing world of African cave-dwelling spiders, focusing on their biology, behavior, and ecological significance.
Tailless Whip Scorpion female with young.
Amblypygi: The Tailless Whip Scorpions
One notable group of cave-dwelling arachnids is the order Amblypygi, commonly known as whip-spiders or tailless whip-scorpions. It's important not to confuse them with whip-scorpions or vinegaroons, which belong to the related order Thelyphonida. The name "amblypygid" means "blunt tail," referring to the absence of the flagellum found in whip-scorpions. As of 2023, around 260 species across five families and 17 genera have been identified.
Habitat and Distribution
Amblypygids are primarily found in tropical and subtropical regions worldwide, favoring warm and humid environments. They prefer to stay hidden in leaf litter, caves, or under bark. Some species are subterranean, and all are nocturnal, avoiding daylight.
Anatomy and Physical Characteristics
Tailless Whip Scorpion Info & Care Damon medius - D. diadema
Being arachnids, Amblypygi possess two main body segments: the prosoma (cephalothorax) and the opisthosoma (abdomen). They have four pairs of legs, pedipalps, and chelicerae. However, only six legs are used for walking, often in a crab-like, sideways motion.
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- Sensory Legs: The first pair of legs are modified into long, thin, antennae-like feelers with numerous fine segments, serving as sensory organs.
- Raptorial Pedipalps: Amblypygids have raptorial pedipalps, similar to the forelegs of mantises, used for grabbing and holding prey. These pedipalps are typically covered in spines, which aid in impaling and capturing prey. The anatomy of the pedipalps varies significantly among species, reflecting different prey capture strategies.
- Exoskeleton: Whip-spiders are covered with a solidified secretion that forms a super-hydrophobic coating. Their exoskeleton is enriched with trace elements such as calcium, magnesium, manganese, potassium, sodium, and zinc, which accumulate as they age.
Pedipalp of a tailless whip scorpion.
Hunting and Feeding Habits
When an amblypygid locates suitable prey with its antenniform legs, it seizes the victim using the spines on its grasping pedipalps, effectively impaling and immobilizing it. The pincer-like chelicerae then grind and chew the prey before ingestion. Remarkably, tailless whip scorpions can survive for over a month without food, often due to pre-molting periods. Their diet primarily consists of arthropods, but they have also been observed feeding on vertebrates, showcasing their opportunistic predatory behavior. Amblypygids generally abstain from feeding before, during, and after molting.
Reproduction and Social Behavior
Courtship in amblypygids involves the male depositing stalked spermatophores onto the ground. These spermatophores have one or more sperm masses at the tip. The male then uses his pedipalps to guide the female over the spermatophores, allowing her to gather the sperm and fertilize her eggs. The female carries the fertilized eggs in a sac under her abdomen (opisthosoma).
Some species, such as Phrynus marginemaculatus and Damon diadema, exhibit social behavior. Research suggests that mother amblypygids communicate with their young using their antenniform front legs, and the offspring reciprocate with both their mother and siblings.
Captive Care
Several genera of Amblypygi, including Acanthophrynus, Charinus, Charon, Damon, Euphrynichus, Heterophrynus, Phrynus, Paraphrynus, and Phrynichus, are popular as pets. When keeping tailless whip-scorpions in captivity, it is essential to provide:
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- Tall enclosures with arboreal climbing surfaces.
- Vertical space for climbing and molting.
- Sufficient space for heat dissipation to maintain a temperature between 70 °F (21 °C) and 75 °F (24 °C).
- A substrate layer of about 5 centimeters (2.0 in) at the bottom of the enclosure for burrowing and water retention to maintain humidity above 75%.
Tailless whip-scorpions typically live between 5 and 10 years.
Discovery of a Spider Megacity in Sulfur Cave
Researchers have recently discovered over 111,000 spiders thriving in what appears to be the world's largest spiderweb, located deep inside Sulfur Cave on the Albanian-Greek border. This discovery marks the first evidence of colonial behavior in two common spider species and likely represents the largest spiderweb ever found. István Urák, an associate professor of biology, described his emotions upon seeing the web as "admiration, respect, and gratitude."
A spiderweb in Sulfur Cave.
The Unique Environment of Sulfur Cave
The spider megacity is situated in Sulfur Cave, a cavern formed by sulfuric acid from the oxidation of hydrogen sulfide in groundwater. Cavers with the Czech Speleological Society initially discovered the giant web in 2022 during an expedition in the Vromoner Canyon. A team of scientists visited the cave in 2024, collecting specimens that Urák analyzed before conducting his own expedition.
Species Living in the Colony
Analysis revealed that two spider species inhabit the colony: Tegenaria domestica, known as the barn funnel weaver or domestic house spider, and Prinerigone vagans. Estimates suggest there are approximately 69,000 T. domestica and over 42,000 P. vagans specimens. DNA analyses confirmed these as the dominant species in the colony.
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Cooperative Behavior
The colony in Sulfur Cave is one of the largest ever documented, and the cooperative behavior between T. domestica and P. vagans is unprecedented. Typically, barn funnel weavers are expected to prey on P. vagans. However, the lack of light in the cave may impair the spiders' vision, leading to a different dynamic. Instead, the spiders feed on non-biting midges, which consume white microbial biofilms from sulfur-oxidizing bacteria in the cave. A sulfur-rich stream, fed by natural springs, flows through the cave, providing hydrogen sulfide and supporting the microbes, midges, and spiders.
Diet and Genetic Adaptation
The spiders' diet influences their microbiomes, making them less diverse compared to spiders of the same species outside the cave. Molecular data also indicates genetic differences, suggesting the cave-dwellers have adapted to their environment.
Preservation
Urák emphasizes the importance of preserving the colony, despite challenges arising from the cave's location between two countries. He notes that unexpected discoveries can still occur, highlighting the remarkable genetic plasticity of some species under extreme conditions.
Other Inhabitants
While spiders may evoke fear in some, many species are harmless to humans. For example, the African Cave dweller, despite its intimidating appearance, lacks venomous fangs. Its pedipalps, similar to those of a mantis, are used to grab and hold prey.
The discovery of the spider megacity in Sulfur Cave underscores the importance of continued exploration and research in extreme environments. The unique adaptations and behaviors of these cave-dwelling spiders offer valuable insights into the resilience and adaptability of life on Earth.
| Species | Common Name | Habitat | Diet | Unique Feature |
|---|---|---|---|---|
| Tegenaria domestica | Barn Funnel Weaver | Caves, Human Dwellings | Non-biting Midges | Colonial Behavior in Sulfur Cave |
| Prinerigone vagans | (Unknown) | Caves, Near Human Dwellings | Non-biting Midges | Co-inhabits webs with T. domestica |
| Amblypygi | Tailless Whip Scorpion | Tropical and Subtropical Regions | Arthropods, Vertebrates | Sensory Front Legs |
