Hairy, Sticky Leg Pads are In: How Different Spiders Hunt

Euophrys_L2_cryo__q17_bearb_color_composite

Spiders are everywhere (Arachnophobes, stop reading now). They’re among the most successful predators on earth today and colonize nearly every terrestrial habitat (that is, not just ceiling corners and under beds), and occasionally do so in numbers large enough to take over small islands. Spider silk may be strong enough to stop a speeding train and some webs, ten times stronger than Kevlar, can be large enough to cross rivers in tropical rainforests.

But more than half of today’s spider species don’t rely on webs or silk to capture their prey. Instead, these hunting spiders have evolved hairy adhesive pads on their legs to grab and hold struggling prey down, according to the results of a recently published PLOS ONE study. The adhesive pads, called scopulae, were commonly seen in many spider species but what wasn’t clear until now was whether they were found in all species, or more likely to occur in hunting spiders.

scopulaeIn this study, researchers used a phylogenetic analysis of spider family trees to correlate different species’ prey capture strategies with the presence or absence of adhesive pads on their legs. They found that the majority of spiders were either web builders or free-ranging hunters, and the latter were most often found to have adhesive hairs on their legs (Apart from these two, at least one rare variety may be mostly vegetarian). Nearly 83% of hunting spiders had adhesive bristles on their legs (compared with 1.1% of web-building varieties). Most of these hunters had either not developed silk-dependent strategies to capture prey, or abandoned web-building for hunting.

Spider Web on PlantWhy would so many spiders abandon an obviously successful way to catch prey? Web-building is a useful way to trap insects and some small mammals, but even to a spider, silk is expensive. Creating a web requires work, damages caused by prey or people need frequent repairs, and certain kinds of webs can require large amounts of silk to be effective. The classic orb-web (seen in the picture here) radically reduced these costs, which may be why the spiders that make these are particularly common. However, this new study reveals that hunting has proved at least as successful a strategy as web-building to more than half of today’s spiders.

Bristly scopulae on hunting spiders’ legs have played a big part in this, enabling spiders to grasp and hold on to struggling prey. The thin bristles on scopulae come in many shapes and forms, and also contribute to these spiders’ mad climbing skills. Read more about which spiders evolved these bristles or learn about other arachnid research published in PLOS ONE here.

 

Citations: Gregori? M, Agnarsson I, Blackledge TA, Kuntner M (2011) How Did the Spider Cross the River? Behavioral Adaptations for River-Bridging Webs in Caerostris darwini (Araneae: Araneidae). PLoS ONE 6(10): e26847. doi:10.1371/journal.pone.0026847

Rogers H, Hille Ris Lambers J, Miller R, Tewksbury JJ (2012) ‘Natural experiment’ Demonstrates Top-Down Control of Spiders by Birds on a Landscape Level. PLoS ONE 7(9): e43446. doi:10.1371/journal.pone.0043446

Wolff JO, Nentwig W, Gorb SN (2013) The Great Silk Alternative: Multiple Co-Evolution of Web Loss and Sticky Hairs in Spiders. PLoS ONE 8(5): e62682. doi:10.1371/journal.pone.0062682

Nyffeler M, Knörnschild M (2013) Bat Predation by Spiders. PLoS ONE 8(3): e58120. doi:10.1371/journal.pone.0058120

Images: Foot of the little jumping spider Euophrys frontalis, credit Jonas Wolffvaried shapes and sizes of bristles on scopulae from pone.0062682spider web on plant by mikebaird

Worth A Thousand Words: Stretchable Spider Silk

Egg sac of the spider Meta menardi.

Spiderman, watch out! There’s a new, super-strength spider silk in town! Researchers from Politecnico di Torino in Italy performed stress tests on the stalks of silk egg sacs produced by the cave spider, Meta menardi (pictured above), and suggest that it could be the most stretchable spider silk ever tested.

The scientists,  led by Dr. Nicola Pugno, collected 15 egg sacs from different caves in Piedmont (a north-western region of Italy), and used a tensile testing machine to pull on the stalk of the sac until the fibers broke. They recorded that silk strands produced by these spiders can stretch up to 7.5 times their original length, which could bode well for future understanding of nano-materials.

The researchers claim that such results may be linked to the fact that these egg sacs were collected from nature, and thus more reflective of actual stresses, as opposed to silk that may have been produced in a lab.

Read the full article here.

PLoS ONE News and Blog Round-Up

Researchers find a possible cure for the common cold and more – in this week’s media digest.

Human Pathogen Shown to Cause Disease in the Threatened Eklhorn Coral Acropora palmata was covered by The NewsHour, The New York Times, NPR, and CNN.

CNET, Hindustan Times, and Okezone covered Automatic Prediction of Facial Trait Judgments: Appearance vs. Structural Models.

The paper, Predator Cat Odors Activate Sexual Arousal Pathways in Brains of Toxoplasma gondii Infected Rats, received coverage from The New York Times, Scientific American, TIME’s Healthland, and The Loom.

Broad-Spectrum Antiviral Therapeutics received media coverage from Voice of America, LA Times, and Forbes.

Large Recovery of Fish Biomass in a No-Take Marine Reserve was covered by National Geographic (nice slideshow too), The Christian Science Monitor, Nature News, and KGTV San Diego. The image above, is taken from Figure 4 of this manuscript.

80 Beats covered the article, Artificial Skin – Culturing of Different Skin Cell Lines for Generating an Artificial Skin Substitute on Cross-Weaved Spider Silk Fibres. So did Treehugger.

The article entitled, Scientists Want More Children received media coverage from The Wall Street Journal, TIME’s Ecocentric, Science Career Blog, and Inside Higher Ed.

Elevated Non-Esterified Fatty Acid Concentrations during Bovine Oocyte Maturation Compromise Early Embryo Physiology was covered by Reuters, The Guardian, and The Press Association.