While many spiders wait for their web to ensnare prey wandering by, other spiders don’t leave their meals up to chance. These arachnids have subtle techniques to lure prey out of their comfort zone and into a trap.
“It’s really a sensory world” for both spiders and their prey, says Pierre-Olivier Montiglio, a behavioral ecologist at the University of Québec at Montréal. “Everybody's constantly eavesdropping and signaling, producing information and communicating it in some way or another.”
Spiders take advantage of this by using their looks, scent, and touch to trick gullible invertebrates straight into their eight arms.
Making webs that shimmer
Webs don’t need to be beautiful to be functional and capture food. But the intricacy of some spiders’ webs, like that of the orb-weaver spiders in the genus Argiope, plays a key role in luring prey to their doom.
Both in the field and in a laboratory setting, scientists have found that webs with more thick white silk band designs in the center hub are more attractive to some prey. The bands serve as decorations that reflect ultraviolet rays which insects are attracted to, according to Mariella Herberstein, a behavioral ecologist at Macquarie University.
The webs themselves are attractive to prey even in the dark, research shows. When testing the webs of Psechrus clavis spiders at night, researchers found that darkening the silk strands made them less attractive to insects flying by. In dark environments, more intricate webs showed they could capture what little light was available, the study shows.
There’s variation in this technique, though, and data suggests decisions about web decorations are strategic. “Some spiders build decorations, and then if they have to build a new web, they might not decorate it again [or] they might decorate it more or less,” says Tom Ratz, a behavioral ecologist at the Ludwig-Maximilians University of Munich. For instance, when there were cues of are a lot of predatorsy birds in the environment, spiders were shown to tone down their decorspiders were shown to tone down their decor, indicating web design was not random.
Using color and patterns to mimic and dazzle
Although many spiders sport dull shades, several species come clad in bright colors and eclectic patterns that help get their prey to come to them.
Jeweled spiders (genus Gasteracantha)get their moniker because they are bedazzled with colors including white, orange, yellow, red, and pink. “They look like little lollies,” says Thomas White, an entomologist at The University of Sydney. “But it's a deceptive signal.”
When these gaudy spiders sit at the center of their woven web, insects passing by are enticed to go have a closer look. White’s work focuses on trying to pinpoint whether the insects are attracted to these vibrant-colored spiders because they’re simply attractive or because they resemble the specific flowers prey would go to for nectar. “It's a tricky thing to untangle,” says White, and it might be a little bit of both.
Studies suggest being colorful helps the nocturnal golden orb-weaver spiders (Nephila pilipes) and spotted orb-web spider (Neoscona punctigera) catch food too. The brown huntsman spider (Heteropoda venatoria), also uses color to deceive its prey: it has a shiny white stripe on its head to lure moths in the dark.
The crab spider species Epicadus heterogaster has evolved to look much like a dainty white flower resting on a leaf, and research suggests its abdomen glitters by reflecting the sun. This glimmer is imperceptible to the human eye, but catches the peepers of bees and flies.
Another species of crab spider, Phrynarachne, has evolved to look like bird droppings instead. While experts have long thought this was a trick to mainly evade predators, researchers have recently discovered it also effectively lures unsuspecting flies looking to lay their eggs in the poop or use it as a source of food.
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Smelling… sexy
Some spiders have evolved to rely less on a potential prey’s eyesight and more on their sense of smell.
Bolas spiders (genus Mastophora) love to munch on moths, but moths’ scaly outer layer of the wingskeeps them from sticking to spiderwebs. So adult female bolas have specialized in luring male moths by producing the pheromones made by female moths looking to mate. Once the moth gets closer to look for their potential partner, Bolas spiders reel them in with a sticky clump of specialized silk.
Different bolas spiders attract different types of moths, and some can attract several different types at once. For instance, Mastophora cornigera can lure in at least 19 different moth species in one single night.
“The question is whether they are producing a master brew of lots of different pheromones, or if they are fine-tuning their signal over the course of the day, or the season,” says Kenneth Haynes, an entomologist at the University of Kentucky. The species he’s studied the most, Mastophora hutchinsoni,produces one type of pheromone early in the night for one moth species, and another completely different pheromone later in the night for another moth species.
Other spider species rely on scent signals to amp up their appeal too. Research suggests the St. Andrew's cross spider (Argiope keyserlingi)sprinkles its silky web with a rotting scent called putrescine to boost the number of flies it captures.
Acting like their prey’s prey or mate
Jumping spiders from the genera Portia, Cyrba, Gelotia, and Brettus like to eat other spider species. But they don’t lure their spider kin onto their own web; they pretend to be stuck in their prey’s web instead. They use their eight legs and two front pedipalps to meticulously pluck the strands to a rhythm that mimics the vibrations a tangled helpless critter would make, luring their spider prey out of its sheltered web center.
“They have an unlimited array of signals that they can make” by plucking their prey’s web, says Fiona Cross, an arachnologist at the University of Canterbury. If Portia spiders are striking a new type of spider, or if the prey isn’t responding, Portia can creatively adjust the signal in real time until it gets the right rhythmcreatively adjust the signal in real time until it gets the right rhythm, according to Cross.
Portia fimbriata also use vibrations to pretend they’re a spider’s potential mate. When they find a nest of a female Euryattus spider—which consists of a rolled-up leaf suspended by a silk thread—they shake the greenery with the vibration signals used by male Euryattus in courting rituals. Portia can imitate this ritual without seeing it before, “even on its first attempt. It's incredible,” says Cross.
Given how cognitively complex these feats are for a critter with a brain the size of a pinhead, the intricacies experts have uncovered about spider behavior are likely just a small slice of all the impressive arachnid trickeries out there.
“It's really hard to actually demonstrate that spiders are using lures,” says Montiglio. “So I guess it’s a good hypothesis to have that the more we study spiders, the more we’ll find spiders are using lures.”
