The strumming assassin that hunts spiders on their own webs
For most insects, walking onto a spider’s web and disturbing the sticky threads would be a very bad idea. The distinctive vibrations of wriggling prey only serve to draw the spider closer and inevitably ends in the insect getting bitten, wrapped in silk and digested. But this story doesn’t always unfold in the spider’s favour. Some vibrations aren’t made by helpless prey, but by an assassin lurking on the web.
The assassin bug (Stenolemus bituberus) is a spider-hunter. Sometimes, it simply sneaks up to spiders on their own webs before striking, plunging its dagger-like mouthparts into its prey. But it also has a subtler technique. Sitting on the web, it plucks the silken threads with its legs, mimicking the frequency of weakly struggling prey. These deceptive vibes are an irresistible draw to the spider, who rush towards their own demise. The bug effectively has a way of ordering for delivery when it doesn’t want to go out for a meal.
Anne Wignall and Philip Taylor from Macquarie University, Sydney, discovered the bug’s tactic earlier this year. To analyse the extent of its deception, they collected several tangle-web spiders from their university grounds and pitted them against the assassins.
They compared the web-strumming actions of the bugs, as well as the struggles of actual prey (a fly and an aphid), the thud of a falling leaf, and the movements of another courting spider. During each encounter, they filmed the action with a high-speed video camera and recorded the vibrations coursing through the web using a laser.
The spiders responded to the bugs in the same way as they did to the fly or the aphid, and just as quickly. They always turned in the right direction, and approached the source of the vibrations most of the time. They almost always ignored the leaves and the behaved very differently to the courtship signals of another spider.
There’s good reason for this. Wignall and Taylor also found that the bugs produce a very specific type of vibration. They’re short, high-pitched and relatively weak, akin to those produced by prey moving their bodies or legs.
These tremors are very different to those produced by falling debris, because they lack any large initial impact wave. They’re more similar to the signals of courting males, but they lack a crucial element – a set of distinctive repeated vibrations – that allows the spiders to spot the advances of their own suitors.
Instead, Wignall and Taylor found that the bugs’ vibrations are most like those of weakly wriggling prey. The assassin bug is a generalist. It doesn’t mimic the struggles of any specific victim, nor does it need to imitate the full range of prey vibrations. All it needs to do is to vibrate the web within the range of characteristics that a spider would recognise as “potential meal”. The spider probably senses the presence of exhausted prey that can’t mount much of a struggle.
The bugs never mimic the large impact of an insect hitting the web, or the initial fierce struggles that it makes as it tries to free itself. This is probably a very good idea. When the spider senses strong vibrations, it often rushes the prey quickly and without pause; the bugs, however, never incited such speedy attacks. That’s a good call; spiders are dangerous prey and they’re sometimes quick enough to launch a counter-attack, killing their would-be assassins. By avoiding the sort of rapid attacks that spiders reserve for their strongest prey, the assassins might minimise the odds of becoming a meal themselves.
Reference: Proc Roy Soc B http://dx.doi.org/10.1098/rspb.2010.2060
Image by dhobern
More on assassin bugs: Assassin bugs deceive spiders with coat of many corpses
If the citation link isn’t working, read why here
//
Related Topics
Go Further
Animals
- Octopuses have a lot of secrets. Can you guess 8 of them?
- Animals
- Feature
Octopuses have a lot of secrets. Can you guess 8 of them? - This biologist and her rescue dog help protect bears in the AndesThis biologist and her rescue dog help protect bears in the Andes
- An octopus invited this writer into her tank—and her secret worldAn octopus invited this writer into her tank—and her secret world
- Peace-loving bonobos are more aggressive than we thoughtPeace-loving bonobos are more aggressive than we thought
Environment
- Listen to 30 years of climate change transformed into haunting musicListen to 30 years of climate change transformed into haunting music
- This ancient society tried to stop El Niño—with child sacrificeThis ancient society tried to stop El Niño—with child sacrifice
- U.S. plans to clean its drinking water. What does that mean?U.S. plans to clean its drinking water. What does that mean?
- Food systems: supporting the triangle of food security, Video Story
- Paid Content
Food systems: supporting the triangle of food security - Will we ever solve the mystery of the Mima mounds?Will we ever solve the mystery of the Mima mounds?
History & Culture
- Strange clues in a Maya temple reveal a fiery political dramaStrange clues in a Maya temple reveal a fiery political drama
- How technology is revealing secrets in these ancient scrollsHow technology is revealing secrets in these ancient scrolls
- Pilgrimages aren’t just spiritual anymore. They’re a workout.Pilgrimages aren’t just spiritual anymore. They’re a workout.
- This ancient society tried to stop El Niño—with child sacrificeThis ancient society tried to stop El Niño—with child sacrifice
- This ancient cure was just revived in a lab. Does it work?This ancient cure was just revived in a lab. Does it work?
Science
- The unexpected health benefits of Ozempic and MounjaroThe unexpected health benefits of Ozempic and Mounjaro
- Do you have an inner monologue? Here’s what it reveals about you.Do you have an inner monologue? Here’s what it reveals about you.
- Jupiter’s volcanic moon Io has been erupting for billions of yearsJupiter’s volcanic moon Io has been erupting for billions of years
- This 80-foot-long sea monster was the killer whale of its timeThis 80-foot-long sea monster was the killer whale of its time
Travel
- How nanobreweries are shaking up Portland's beer sceneHow nanobreweries are shaking up Portland's beer scene
- How to plan an epic summer trip to a national parkHow to plan an epic summer trip to a national park
- This town is the Alps' first European Capital of CultureThis town is the Alps' first European Capital of Culture
- This royal city lies in the shadow of Kuala LumpurThis royal city lies in the shadow of Kuala Lumpur