Spiders

Psychological Drivers of Arachnophobia

• Public Perception vs. Actual Human Risk:

  • Spiders elicit some of the strongest phobic emotional responses from the general public among all animal groups covered in the unit (spiders, snakes, crocodiles, sharks).

  • Australian Geographic Killer Oz Reference Text: Contains $50$ distinct vignettes detailing animal distribution maps and basic biology. The Redback spider is featured on the cover.

  • Fatality Data: Zero confirmed deaths from Redback spider bites since the $1950\text{s}$. Zero confirmed deaths from any spider envenomation in Australia since $1981$.

• Mechanisms of Fear (Swedish Research Findings):

  • Pop Culture Tropes: Movies such as Arachnophobia (1990 tagline: "Eight legs, two fangs, and an attitude") and internet memes ("Kill it with fire") reinforce extreme avoidance. A documented real-world case in the United States involved a man setting fire to his own house attempting to burn a spider.

  • Clinical Arachnophobia vs. Mild Discomfort: Mild discomfort ("heebie-jeebies") is common, but clinical arachnophobia causes crippling anxiety disrupting daily life. Clinical management utilizes systematic desensitization (sequential exposure: photographs $\rightarrow$ dead specimens $\rightarrow$ live specimens).

  • Path Analysis Findings on Fear Drivers:

  • Primary Drivers: Physical appearance (body size, visual shape profile) and locomotion dynamics (erratic movement, skittishness, sudden proximity).

  • Non-Significant Drivers: Coloration, hairiness, and real vs. fake distinctions (fake spiders trigger comparable fear responses; hairiness shows minimal statistical impact).

  • Psychological Conclusion: Arachnophobia is driven by an intrinsic psychological and visual response to physical form and movement mechanics rather than an accurate assessment of venomous threat.

Diversity, Morphology, and Adaptations of Spiders

• Global and Australian Biodiversity Numbers:

  • Described Global Species: Approximately $50\!{,}000$ named spider species globally.

  • Estimated Total Global Species: Between $100\!{,}000$ and $200\!{,}000$ species (including undescribed species).

  • Australian Described Species: At least $2\!{,}000$ named species native to Australia.

  • Recent Field Expeditions: A single travel expedition to Cape York uncovered $50$ brand-new undescribed spider species.

  • Course Focus: Focuses specifically on $4\text{ to }5$ major groups out of Australia's vast spider diversity.

• Key Morphological & Behavioral Examples:

  • Jungle Huntsman Spiders: Northern Queensland species; large, non-aggressive house dwellers that wander homes to feed on cockroaches; feature prominent forward-facing eyes.

  • Peacock Spiders: Miniature jumping spiders measuring $3\,\text{mm}$ to $4\,\text{mm}$ in body length; males perform elaborate visual courtship dances. Popularized by a biosecurity entomologist stationed at Mascot inspecting agricultural imports.

  • Net-Casting Spiders: Highly visual predators that weave a small, stretchable silk net held in their front legs to manually snare passing prey.

  • Large-Jawed Spiders: Characterized by prominently elongated chelicerae.

  • Mirror Ball Spiders: Feature a reflective, multi-faceted abdomen resembling a disco ball.

  • Jumping Spiders: Possess large, prominent anterior median eyes providing high visual acuity.

  • Golden Orb Weavers: Common urban specialists that thrive in metropolitan environments and man-made structures.

Medically Significant Australian Spider Groups

• Primary Groups Covered in Course, can all be found in New South Wales:

  1. Funnel-Web Spiders

  2. Redback Spiders

  3. Mouse Spiders

  4. White-Tailed Spiders (included with caveats regarding overstated risks)

• Funnel-Web Spiders (Atrax / Aetrex Species):

  • Taxonomic Reclassification: Historically classified as a single species (Aetrex robustus or Atrax robustus, the Sydney Funnel-Web) ranging from Shoalhaven to Newcastle. Research led by Mike Gray (Australian Museum) and the Australian Reptile Park split them into $3$ distinct species based on Central Coast/Newcastle population size differences, molecular genetics, and morphology.

  • Diagnostic Anatomy: Species differentiation relies heavily on the shape of the male embolus (sperm delivery organ located on the palpal mouthparts).

  • Structural Distinction — Mygalomorphs vs. Araneomorphs:

  • Mygalomorphs (Funnel-webs, Mouse spiders): Possess parallel fangs that strike straight downward. Must rear back on hind legs to strike.

  • Araneomorphs ("Modern spiders"): Possess opposing pincer-like fangs that move horizontally/inward.

  • Toxicity & Primate Vulnerability:

  • Bites are mechanically painful due to large fangs; dry bites (without venom injection) occur frequently.

  • Venom contains a neurotoxin specifically toxic to primates. This is an accidental evolutionary overlap, as primates are not natural prey.

  • Neurotoxin affects the human nervous system by holding the sodium channels open in cells, leading to exhaustion of neurotransmitters.

  • Males are significantly more toxic than females and wander actively in search of mates.

  • Symptoms of envenomation include tingling, twitching (especially of the tongue), muscle spasms, salivation, sweating, goosebumps, laboured breathing, raised or lowered heart rate, and expanded or contracted pupils.

  • First aid procedure for a bite is to treat immediately with a pressure immobilisation bandage.

  • Environmental Dynamics: Warmer, wetter weather floods subterranean burrows, driving males to wander earlier in the season. Climate shifts increase human encounters and public health concerns (e.g., mosquito-borne diseases and venomous animal movements).

  • Venom has been used to create insecticide.

• Mouse Spiders:

  • Closely related to Funnel-webs within the Mygalomorph group.

  • Discernable from the funnel web as the mouse spiders have extremely broad, bulbous chelicerae.

  • Medically significant; possess massive chelicerae capable of delivering severe mechanical bite trauma even without envenomation.

  • Similar compounds in it’s venom to the Funnel-webs, but bites result in only mild symptoms.

  • Males feature bright, vivid head/body coloration during wandering phases.

• Redback Spiders (Latrodectus hasseltii):

  • Taxonomy: Member of the cosmopolitan Black Widow family (Latrodectus).

  • Identification: Dark body with a distinct longitudinal orange/red stripe on the dorsal abdomen.

  • Envenomation Dynamics: Envenomations are delivered almost exclusively females; males are tiny and frequently consumed by females during mating as a nuptial gift.

  • Female redback is responsible for majority of medically important spider bites in Australia. Redback spider bites are 4 times more common than funnel-web spider bites.

  • Symptoms of being biten and envenomated is called latrodectism. Symptoms include slow onset of pain (probably won’t feel the initial bite) that can last for days and disrupt sleep, diaphoresis (excessive sweating), nausea, headache, vomiting, and in rare cases priapism (extended, painful erection.

  • Bites can be treated with an ice pack.

  • Web Architecture: Three-dimensional web consisting of an upper structural platform attached to a wall and vertical elastic trap-lines coated with adhesive droplets reaching the floor.

  • Habitat & Synanthropy: Highly commensal with human built environments (garages, outhouses, walls). Natural habitats include sandstone escarpments, dry rock crevices, hollows, and Northern Territory termite mounds. Historical hypotheses suggest rapid population expansion or late arrival around the $1940\text{s}$ or $1950\text{s}$.

  • Cultural References: Popularized in Australia by Slim Newton's song "Redback on the Toilet Seat".

• White-Tailed Spiders:

  • Myth vs. Evidence: Historically accused of causing necrotising arachnidism (flesh-eating tissue ulcers).

  • Scientific Consensus: Medical research disproves necrotising claims; white-tail bites do not cause tissue necrosis or severe bacterial rotting. Ulcers historically attributed to bites are typically caused by unrelated conditions, such as Buruli ulcer infections.

Student Q&A, Visual Ecology, and Course Action Items

• Padlet & In-Class Q&A Interactions:

  • Question: Is there a difference in deadliness between Mygalomorphs and Araneomorphs?

  • Answer: Mygalomorphs (e.g., Funnel-webs) generally possess venom far more toxic to humans and primates than Araneomorphs, though overall spider fatalities across both groups remain virtually non-existent (zero deaths since $1981$).

• Visual Ecology & Urban Adaptation:

  • Net-casting spiders and jumping spiders rely on visual hunting. Modern research is investigating how Artificial Light at Night (ALAN) affects orb-weaving spider vision, behavior, and urban evolution.