Spiders customise webs based on diet
DEPENDING ON THEIR nutrient needs, spiders can customise their webs to catch different types of prey, new research suggests.
Spider webs are specialised tools for catching prey and each species has its own unique web it uses catch its ideal prey. Some species spin huge nets to capture flying insects, whereas others construct elaborate booby traps to catch prey walking on the ground.
Individual spiders can also change the structure and composition of their webs. Sometimes they are huge and sometimes they are small, sometimes soft and elastic, other times thick and rigid, sometimes they are sticky and other times less so. And it has been a curiosity as to why spiders alter their webs.
New research out this week in the journal Royal Society Open Science suggests that it’s the nutrients in a spider’s diet that affect the types of webs they spin.
“We were interested in whether behavioural interactions with their prey or the types of nutrients the spiders were getting could act as cues that make spiders build different types of webs” says lead researcher Dr Sean Blamires from the University of New South Wales.
In other words, if more flies were around, would spiders make better fly-catching webs?
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There was a spider that caught a fly
Researchers fed either lipid-rich crickets or protein-rich flies to giant wood spiders (Nephila pilipes) collected in Taiwan. They found that spiders fed a diet of flies built larger webs with more silk. Spiders that fed on crickets tended to build smaller but stickier webs with more glue droplets.
By measuring what parts of the prey spiders ate and what they left behind the researchers could estimate how much protein, lipids and carbohydrates the spiders were actually eating.
The researchers were surprised to find that spiders were selective in what they ingested; some spiders were extracting more protein and less carbohydrate from their prey, whereas others were taking more lipids. The spiders that ate more protein tended to build larger webs, and those taking relatively little protein built smaller, sticker webs.
Spider webs designed to catch particular prey
So it seems that spiders are counting their calories and modifying their webs to suit. The findings indicate that spiders adjust the type of webs they spin to adapt to what food source is around. If there are more flies, for example, spiders don’t seem to waste the extra energy needed to build stronger, stickier webs.
Alternatively, spiders may actually be targeting crickets or spiders, depending on their energy needs.
“It’s possible that there is an enforced compromise where protein intake limits the web they can build,” says Sean. “On the other hand, it could be a foraging strategy to try to catch certain types of prey.”
Associate Professor Marie Herberstein from Macquarie University, an expert on spider behaviour and evolution, says that this new research provides insight into spider web evolution.
“Major changes in the nutritional landscape of spiders (e.g. the loss of a major prey group or the introduction of a new prey group) may lead to the evolution of new webs and silks,” says Marie.
