Before one species of jumping spider, known as Evarcha culicivora, goes trolling for a mate, it firsts look to feast on blood-fattened mosquitoes. What happens next seems like something out of a bad video game: The delicacy gives the spider a special power–a sweet smell that the opposite sex finds irresistible.
In a new study, which will be published in the Proceedings of the National Academy of Sciences, researchers exposed E. culicivora specimens to the odors of others raised on blood-fed female mosquitoes and on three other diets: sugar-fed females, males and lake flies…. [The] tested spiders of both sexes were most strongly attracted to the odor of spiders reared on blood-fed female mosquitoes. But the attraction was only for spiders of the opposite sex [The New York Times]. Spiders would hang around blood-fattened spiders of the opposite sex four times longer than they would linger around those fed on another diet. The blood perfume effect might only be triggered by a gender specific hormone, the researchers suggest.
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A jumping spider that passes on eating ants in favor of leafy greens has just been described by scientists. The novel arachnid, named Bagheera kiplingi, is exciting because it is the first-known predominantly vegetarian spider; all of the other known 40,000 spider species are thought to be mainly carnivorous [BBC News]. The study was published in the journal Current Biology.
Found in Central America and Mexico, the order-defying jumping spider eats nutrient-rich structures called Beltian bodies, which are found on the tips of Acacia trees. Trees produce the bodies to feed ants that defend them, which is a textbook example of what’s called co-evolutionary mutalism, and one that B. kiplingi has evolved to exploit [Wired.com]. Despite a primarily veggie diet, B. kiplingi actively hunts its green prey, which sounds bizarre, since the leaves can’t run away. The spider first sits and stalks its target before it dodges through the ant defenses, snatches a Beltian body, and flees to safety.
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Males of the spider species Harpactea sadistica have a violent way of increasing their odds of reproductive success. In the midst of a mating tussle, the male stabs his spiked copulatory organ (pictured) into the abdomen of the female, in order to deposit his sperm directly into the female’s ovaries.
This process, known as traumatic insemination, is common among many hermaphrodite species as well as some insects with separate sexes, most famously the bed bug. But it has never before been observed in other arthropods. “Now we have a very odd biological phenomenon in an unrelated taxonomic group…. It’s like finding a peacock’s tail in a non-bird species” [The Scientist], says Mike Siva-Jothy, who has observed the behavior in bed bugs.
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Scientists have managed to make extra-strength spider silk—already notable for having a tensile strength higher than many alloys of steel, even though its comprised entirely of proteins [Ars Technica]—by incorporating small amounts of metal into it. A research team at the Max Planck Institute was inspired by studies showing traces of metals in the toughest parts of some insect body parts. The jaws of leaf-cutter ants and locusts, for example, both contain high levels of zinc, making them particularly stiff and hard [Reuters]. The researchers wanted to try adding metals into existing biological materials, and decided to start with the Araneus spider.
The researchers, whose work is published in Science, used atomic-layer deposition to pulse zinc, titanium, and aluminum ions into spider silk [Technology Review]. The process is used normally to apply a thin film layer of one material onto another, but the researchers found that the metal ions had actually penetrated and reacted with the protein structure of the silk, yielding a material significantly stronger than natural spider silk, though they don’t quite understand how the integration occurred. One of the researchers, Mato Knez, attributes the strengthening effect to the metal’s displacement of hydrogen bonds within the silk’s protein structure…. The team were also able to show that the outer metal coating of the silk was of minor importance in the improvement of strength, and therefore that the phenomena was caused by the metals imbedded in the protein fibres [Chemistry World].
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Paleontologists have taken another hard look at the fossilized remains of an arachnid that lived 386 million years ago, and have stripped away its title as the oldest known spider. The creature, Attercopus fimbriunguis, was originally believed to have the capacity to spin webs out of silk, but a reconsideration of the fragmented fossil has led researchers to conclude that Attercopus could make silk, but probably excreted it in sheets. These proto-spiders may have used sheets of silk to line burrows, wrap eggs or even to have sex [Nature News].
Previous studies had suggested that the Attercopus had a single spinneret, the appendage that spiders use to weave silk into webs. But lead researcher Paul Selden studied newly discovered fossil fragments and realized that those previous researchers were mistaken. The tiny hollow hairs that excrete spun silk, called spigots, are arranged in a double row on plates lining Attercopus’s belly, and what had been identified as a spinneret was actually a plate folded over. Without spinnerets, the creatures could not have precisely controlled the emerging silk. “It would have been much less manoeuvrable,” says Selden [Nature News].
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Cannibalistic female spiders who chow down on males do so to give their fertilized eggs a developmental boost, a new study suggests. Researchers found that those Mediterranean tarantulas who ate their suitors produced more offspring, and those spiderlings were stronger and bigger than the offspring of tarantulas that had stuck to more natural prey.
The study turned up several surprises. The researchers watched the tarantulas’ behavior in their natural environments, and saw that the female spiders didn’t eat their mates–instead they waited until after they had mated, and then devoured the next unlucky suitor who came along. Some other studies have suggested that males may sacrifice themselves for the sake of their offspring, but this study showed that, at least in this species of spider, the males are purely unlucky victims and only the babies benefit [Reuters].
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