Orb weaver spiders are known for their big, beautiful webs. Now, researchers suggest that these webs do more than just glue a spider’s meal in place — they may also swiftly paralyze their catch.
Biochemical ecologist Mario Palma has long suspected that the webs of orb weavers — common garden spiders that build wheel-shaped webs — contain neurotoxins. “My colleagues told me, ‘You are nuts,’” says Palma, of São Paulo State University’s Institute of Biosciences in Rio Claro, Brazil. No one had found such toxins, and webs’ stickiness seemed more than sufficient for the purpose of ensnaring prey.
The idea first came to him about 25 years ago, when Palma lived near a rice plantation where orb weavers were common. He says he often saw fresh prey, like bees or flies, in the spiders’ webs, and over time, noticed the hapless animals weren’t just glued — they convulsed and stuck out their tongues, as if they’d been poisoned. If he pulled the insects free, they struggled to walk or hold up their bodies, even if the web’s owner hadn’t injected venom.
Palma had worked with neurotoxins for many years, and these odd behaviors immediately struck him as the effects of such toxins.
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Now, thanks in large part to the work of his Ph.D. student Franciele Esteves, Palma thinks he has found those prey-paralyzing toxins. The pair and their colleagues analyzed the active genes and proteins in the silk glands of banana spiders (Trichonephila clavipes) — a kind of orb weaver — and found proteins resembling known neurotoxins. The neurotoxins may make the webs paralytic traps, the team reports online June 15 in the Journal of Proteome Research. The prey-catching webs of other species probably have similar neurotoxins, Palma says.
These neurotoxin proteins also showed up on the silk of webs collected in Rio Claro, packed into fatty bubbles in microscopic droplets on the strands. And when the researchers rinsed substances from webs and injected them into bees, the animals became paralyzed in less than a minute.
The researchers also confirmed, as Palma’s lab had reported in 2006, that fatty acids are present in the droplets. These acids, Palma thinks, are the toxins’ way into prey. The molecules may dissolve the insect’s waxy outer cuticle, the chief barrier to topical toxins.
“Toxic webs would certainly make sense,” says David Wilson, a venom researcher at James Cook University in Cairns, Australia, but he’d like to see evidence that the web toxins work quickly on contact. Alternatively, they might act as antimicrobials (SN: 10/30/19) or help deter ants and other animals that steal from webs or eat the spiders.
Jolanta Beinaroviča, a synthetic spider silk designer at the University of Nottingham in England, says, “This paper was like a breath of fresh air.” She thinks many researchers have long oversimplified spider web silks, though she, too, would like to see further demonstration of the toxins’ topical action.
Paralytic toxins may be just part of the underappreciated complexity of web design. Palma plans to have his students dive deeper into smaller, as of yet unidentified proteins his team found. He thinks they may help keep the prey alive until the spider’s ready for a fresh meal.