tag:theconversation.com,2011:/us/topics/pitcher-plants-5655/articlespitcher plants – The Conversation2018-04-16T10:54:41Ztag:theconversation.com,2011:article/948582018-04-16T10:54:41Z2018-04-16T10:54:41ZNo more water stains – we found a new way to control evaporation using maths<figure><img src="https://images.theconversation.com/files/214754/original/file-20180413-46652-u5167w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><p>Water stains are the bane of every proud car owner or dinner party host, left behind by raindrops drying on a vehicle’s surface or rinse water on a wine glass. But <a href="https://www.nature.com/articles/s41467-018-03840-6">we have discovered</a> a new way of controlling the evaporation of liquid droplets that causes water marks using a <a href="https://theconversation.com/uk/topics/biomimetics-7729">technology inspired by nature</a>. Our research could not only produce new treatments for minimising water stains on cars but also find other applications such as improving cooling devices used to <a href="https://celsiainc.com/blog-using-heat-pipes-and-fans-to-cool-smartphones">prevent smartphones overheating</a>.</p>
<p>The droplet evaporation process that forms water marks seems simple but involves a complex interplay between heat transfer, fluid flow and surface friction. <a href="http://hyperphysics.phy-astr.gsu.edu/hbase/Kinetic/vappre.html">Water evaporates</a> when the molecules at its surface have enough energy to break free from the liquid and become water vapour. To gain this energy, the water absorbs heat from its surroundings, which is why <a href="http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/sweat.html">sweat cools you down</a>.</p>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/214460/original/file-20180412-554-5mcfoz.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/214460/original/file-20180412-554-5mcfoz.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=422&fit=crop&dpr=1 600w, https://images.theconversation.com/files/214460/original/file-20180412-554-5mcfoz.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=422&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/214460/original/file-20180412-554-5mcfoz.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=422&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/214460/original/file-20180412-554-5mcfoz.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=530&fit=crop&dpr=1 754w, https://images.theconversation.com/files/214460/original/file-20180412-554-5mcfoz.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=530&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/214460/original/file-20180412-554-5mcfoz.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=530&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A water mark appears due to “pinning” of the droplet edge on a rough solid surface.</span>
<span class="attribution"><span class="source">Author provided</span></span>
</figcaption>
</figure>
<p>As a water droplet evaporates, any non-water particles in the liquid are drawn to its outer edge and are left behind as a ring of residue, a water mark. This happens because even seemingly smooth surfaces are actually quite rough on a microscopic scale. The bottom layer of a droplet’s edge will cling to the jagged surface while the molecules above it evaporate.</p>
<p>Water from the middle of the droplet then flows outward to replace the evaporated molecules, carrying with it solid particles and depositing them on the surface as the liquid finally dries up. This means the key to preventing water marks is creating surfaces that stop the edge of the droplet from clinging to the surface by controlling its shape and position during evaporation.</p>
<figure>
<iframe src="https://player.vimeo.com/video/264093950" width="500" height="281" frameborder="0" webkitallowfullscreen="" mozallowfullscreen="" allowfullscreen=""></iframe>
<figcaption><span class="caption">How snap evaporation works.</span></figcaption>
</figure>
<p>To tackle this issue, as with other projects in our lab, we drew inspiration from biological systems to create a material that mimicked useful properties found in nature. In this case, we used surfaces inspired by the pitcher plant, a carnivorous plant that <a href="https://pubs.acs.org/cen/news/89/i39/8939-20110921lnp1.html">grows in tropical rainforests</a>.</p>
<figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/214459/original/file-20180412-554-1lb2cl1.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/214459/original/file-20180412-554-1lb2cl1.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=800&fit=crop&dpr=1 600w, https://images.theconversation.com/files/214459/original/file-20180412-554-1lb2cl1.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=800&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/214459/original/file-20180412-554-1lb2cl1.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=800&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/214459/original/file-20180412-554-1lb2cl1.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1005&fit=crop&dpr=1 754w, https://images.theconversation.com/files/214459/original/file-20180412-554-1lb2cl1.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1005&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/214459/original/file-20180412-554-1lb2cl1.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1005&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The slippery pitcher plant.</span>
<span class="attribution"><span class="source">Jeremiah, Wikmedia Commons</span></span>
</figcaption>
</figure>
<p>The pitcher plant has a micro-structure on its surface that traps a thin layer of lubricating liquid, making it super slippery. As a result, insects that land on the plant’s surface slip and fall into a pitcher-shaped cavity, where they are digested by the plant.</p>
<p>In the lab, we created slippery surfaces that also trap a thin lubricant layer. On these surfaces, the evaporation of droplets becomes very uniform and the non-water particles gather in a speck rather than a ring-shaped water mark. </p>
<p>Next we looked for a way to control the location of the droplets as they evaporated, which can be used to minimise the visibility of these specks. To do this, we built a slippery surface shaped in a repeating wavy pattern of peaks and valleys. As the droplets evaporate and shrink, they snap into a new shape and location whenever their edge passes one of the peaks.</p>
<p>We were then able to work out how the shape and position of each droplet would change with each snap. This meant we could design a surface that would guide the droplets into the right place through a series of coordinated snaps.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/214470/original/file-20180412-540-1a2lp8g.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/214470/original/file-20180412-540-1a2lp8g.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/214470/original/file-20180412-540-1a2lp8g.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=115&fit=crop&dpr=1 600w, https://images.theconversation.com/files/214470/original/file-20180412-540-1a2lp8g.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=115&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/214470/original/file-20180412-540-1a2lp8g.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=115&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/214470/original/file-20180412-540-1a2lp8g.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=144&fit=crop&dpr=1 754w, https://images.theconversation.com/files/214470/original/file-20180412-540-1a2lp8g.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=144&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/214470/original/file-20180412-540-1a2lp8g.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=144&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Snap evaporation on an egg-box surface. The shape and position of the drying droplet is controlled by the underlying slippery wavy solid.</span>
<span class="attribution"><span class="source">Author provided</span></span>
</figcaption>
</figure>
<p>To understand what causes the snaps, we looked into a branch of mathematics called <a href="https://blog.waves.kit.edu/wp/index.php/2017/01/24/what-is-bifurcation-theory/">bifurcation theory</a>. This involves studying how a system responds when a parameter changes. In this case, we looked at how the droplet responds when its mass shrinks as the water evaporates.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/214458/original/file-20180412-566-mhvrnd.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/214458/original/file-20180412-566-mhvrnd.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/214458/original/file-20180412-566-mhvrnd.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=1268&fit=crop&dpr=1 600w, https://images.theconversation.com/files/214458/original/file-20180412-566-mhvrnd.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=1268&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/214458/original/file-20180412-566-mhvrnd.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=1268&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/214458/original/file-20180412-566-mhvrnd.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1593&fit=crop&dpr=1 754w, https://images.theconversation.com/files/214458/original/file-20180412-566-mhvrnd.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1593&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/214458/original/file-20180412-566-mhvrnd.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1593&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The same droplet can take many shapes and positions on a wavy surface. The black profiles correspond to shapes which are unstable.</span>
<span class="attribution"><span class="source">Author provided</span></span>
</figcaption>
</figure>
<p>Our idea is that, as the mass reduces, the droplet eventually reaches a certain point (a bifurcation) where it can no longer maintain its current shape or position and must change into another configuration. The wavy surface acts as a steering wheel, guiding the droplet through a sequence of stable configurations.</p>
<p>Our research could have an impact on many everyday applications, and we are currently working with industrial partners that can benefit from our research. For example, we are working with car manufacturers to develop ways to provide vehicle surfaces with a pattern that minimises water marks. We are also working with engineers that build heat-removal systems based on evaporation, such as those used to cool the microchips in smartphones, to improve their efficiency.</p>
<p>But for now you’ll still have to dry your wine glasses with a tea towel if you want to make a spotless impression.</p><img src="https://counter.theconversation.com/content/94858/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Rodrigo Ledesma-Aguilar receives funding from the UK's Engineering and Physical Sciences Research Council. He works for Northumbria University.</span></em></p>Microscopically engineering surfaces could stop water leaving behind rings of residue as it dries.Rodrigo Ledesma-Aguilar, Associate Professor, Northumbria University, NewcastleLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/361812015-01-14T16:04:20Z2015-01-14T16:04:20ZHow working part-time makes pitcher plants more effective ant killers<figure><img src="https://images.theconversation.com/files/69030/original/image-20150114-3865-1ioa7l8.JPG?ixlib=rb-1.1.0&rect=0%2C24%2C1257%2C868&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Tempting traps.</span> <span class="attribution"><span class="source">U. Bauer</span></span></figcaption></figure><p>Sometimes less can be more. <a href="https://theconversation.com/the-strange-world-of-the-carnivorous-plant-15607">Carnivorous pitcher plants</a> from the tropical island of Borneo (Brunei) demonstrate this quite impressively. These plants use funnel-shaped pitfall traps, or pitchers, with slippery slopes to capture insects. Once they slip, the insects drown in a pool of digestive liquid and the plants feed on the released nutrients. </p>
<p>This unusual feeding strategy allows <a href="http://www.carnivorous--plants.com/pitcher-plant.html">pitcher plants</a> to survive on extremely poor soils where other, “normal” plants struggle. Because pitcher plants rely so heavily on capturing prey, one should expect their traps to be optimised for catching as much prey as possible. So it came as a surprise that the most widespread trapping surface is only slippery when it is wet by rain or condensation, but not when dry.</p>
<p>When I went out to study <em><a href="http://nepenthes.merbach.net/english/_rafflesiana.html">Nepenthes rafflesiana</a></em> pitcher plants in Borneo for my PhD project in 2006, I noticed that the trapping surfaces were dry and safe for insects to walk on for up to eight hours a day. Did pitcher plants just fail to evolve a better solution, or did they evolve in a constantly wet environment and are now living under sub-optimal conditions? </p>
<p>Evolutionary “failure” can be ruled out rather quickly. Many species possess other, slippery surfaces independent of wetness – and the young seedlings of <em>N. rafflesiana</em> use permanently slippery wax crystal surfaces for trapping prey. The mature plants, however, have lost the wax crystals and rely entirely on the trapping surface becoming wet through rain or dew. So why do the plants “abandon” an effective trapping device in favour of a seemingly flawed one?</p>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/69031/original/image-20150114-3856-1kq8zvx.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/69031/original/image-20150114-3856-1kq8zvx.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=900&fit=crop&dpr=1 600w, https://images.theconversation.com/files/69031/original/image-20150114-3856-1kq8zvx.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=900&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/69031/original/image-20150114-3856-1kq8zvx.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=900&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/69031/original/image-20150114-3856-1kq8zvx.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1131&fit=crop&dpr=1 754w, https://images.theconversation.com/files/69031/original/image-20150114-3856-1kq8zvx.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1131&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/69031/original/image-20150114-3856-1kq8zvx.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1131&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">It’s dinner time.</span>
<span class="attribution"><span class="source">U. Bauer</span></span>
</figcaption>
</figure>
<p>The key to the answer lies in the plant’s prey, as we found in a new study published in the <a href="http://rspb.royalsocietypublishing.org/content/282/1801/20142675">Proceedings of the Royal Society</a>. For many pitcher plant species, including <em>N. rafflesiana</em>, ants are the major prey. As social insects, ants live in colonies with a clear division of labour. Only the queen reproduces – while other vital tasks, such as foraging, brood care or defence, are carried out by various worker castes. In order to find lucrative food sources, the colony sends out “scout” ants that explore the surroundings of the nest. </p>
<p><em>Nepenthes</em> pitchers produce a lot of sweet nectar to attract insects. If a scout ant arrives at a pitcher during dry times, it can safely return to the colony and lead its fellow ants to the nectar source. When the trap gets wet and slippery later, these followers get caught in one sweep. In contrast, a trap that is super-slippery at all times would capture the scout ants, thereby cutting off its own “prey supply”.</p>
<p>We tested this idea by fitting some pitchers in the field with a hospital drip that kept the trapping surface wet at all times. We then compared the amount of prey caught by these pitchers with that caught by natural, alternately wet and dry pitchers. We found that naturally alternating traps caught in total almost 2.5 times as many ants as the constantly wet ones. This was not evenly distributed though: most traps caught hardly any ants, regardless of the conditions. However, under natural conditions where the plants’ trapping surfaces are alternately wet and dry, a few pitchers made spectacular catches, occasionally more than 100 ants within just two days. This never happened when the traps were kept constantly wet.</p>
<p>Constantly wet traps, in contrast, captured more non-recruiting prey such as flies, stingless bees or beetles. This makes sense because the wet traps were “active” for longer, increasing the chance of capturing random visitors. Nevertheless, this moderate increase in non-ant prey through constant wetting could not offset the loss of ant prey: overall, naturally alternating traps caught 36% more prey than wet traps. Such a stark difference explains why a mechanism that at first sight seems disadvantageous, can persist in evolution.</p><img src="https://counter.theconversation.com/content/36181/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ulrike Bauer receives funding from The Leverhulme Trust and the Rank Prize Funds. The field work leading to the present study has been partly funded by the Cambridge Philosophical Society, Trinity College Cambridge, The Balfour Trust, The Mark Pryor Fund, The Charles Slater Fund, The German Academic Exchange Service and the British High Commission in Brunei.
Ulrike Bauer is a Leverhulme Early Career Fellow at the University of Bristol and a Research Associate at Universiti Brunei Darussalam.</span></em></p>Sometimes less can be more. Carnivorous pitcher plants from the tropical island of Borneo (Brunei) demonstrate this quite impressively. These plants use funnel-shaped pitfall traps, or pitchers, with slippery…Ulrike Bauer, Leverhulme Early Career Fellow, University of BristolLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/156072013-07-01T05:42:07Z2013-07-01T05:42:07ZThe strange world of the carnivorous plant<figure><img src="https://images.theconversation.com/files/26463/original/qr8b26cj-1372438796.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Actual botany is not like this.</span> <span class="attribution"><span class="source">Rank Organisation/Allied Artists</span></span></figcaption></figure><p>Ever since their discovery, carnivorous plants have fascinated scientists and spurred the imagination of artists, writers and filmmakers. While the <em>Puya chilensis</em> cactus at the Royal Horticultural Society Garden in Wisley, Surrey, that <a href="http://www.bbc.co.uk/news/uk-england-surrey-22967160">recently blossomed</a> for the first time in 15 years has been breathlessly reported as a “sheep-eating” cactus (they are merely entangled in its velcro-like spines), the reality of carnivorous plants is often considerably stranger than fiction.</p>
<p>Triffids and monster plants exist only in novels and horror movies, but real carnivorous plants have evolved an impressive arsenal of tricks and traps that are absolutely deadly to insects, and sometimes even small vertebrates. Using these, carnivorous plants can survive in places where nutrients are scarce and other plants struggle to thrive. Their high diversity (more than 600 species in five different plant orders) and global distribution from Arctic tundra to equatorial rainforests testifies to the success of their evolutionary niche.</p>
<p>The startling methods they use to <a href="http://www.worldcat.org/title/carnivorous-plants/oclc/490279526?referer=di">trap their prey</a> range from the millimetre-sized suction traps of <a href="http://www.britannica.com/EBchecked/topic/68677/bladderwort">bladderworts</a>, to those with pitchers - leaves shaped like hollow containers filled with liquid to drown and digest prey - such as the <a href="http://www.botany.org/Carnivorous_Plants/Sarracenia.php"><em>Sarracenia</em></a> pitchers, to the archetypal <a href="http://www.britannica.com/EBchecked/topic/625756/Venuss-flytrap">Venus fly trap</a>.</p>
<p>Some species employ sophisticated trapping mechanisms, including some of the fastest known movements in plants. Others simply wait for prey to get caught on sticky secretions or slip into pitfall traps. But recent scientific discoveries have shown that there is more to those “simple” mechanisms than one might think.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/ktIGVtKdgwo?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The Venus flytrap - a fast mover.</span></figcaption>
</figure>
<p>The interior of many Asian <em>Nepenthes</em> pitchers is lined with a conspicuous crystalline wax coating that renders it extremely slippery for insects. Scanning electron micrographs have revealed a dense array of minute, upright wax platelets that create an extremely fine surface roughness that minimises the available contact area for the adhesive pads of insects’ feet. Insect pads do not stick well to rough surfaces – much like Sellotape does not stick well to a sandpaper surface - and they slip.</p>
<figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/26459/original/g3rftrx9-1372436788.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/26459/original/g3rftrx9-1372436788.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=900&fit=crop&dpr=1 600w, https://images.theconversation.com/files/26459/original/g3rftrx9-1372436788.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=900&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/26459/original/g3rftrx9-1372436788.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=900&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/26459/original/g3rftrx9-1372436788.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1131&fit=crop&dpr=1 754w, https://images.theconversation.com/files/26459/original/g3rftrx9-1372436788.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1131&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/26459/original/g3rftrx9-1372436788.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1131&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">An ant collects sweet nectar from the glands of the <em>N. rafflesiana</em> pitcher plant, positioned so that the ants stand dangerously close to the mouth of the trap.</span>
<span class="attribution"><span class="source">Ulrike Bauer</span></span>
</figcaption>
</figure>
<p>Likewise, the roughness of the waxy inside of the pitcher wall is too fine for insects’ claws to grab hold, and the waxy crystals are attached to brittle stalks that break off easily, making it even harder for the insect to find a footing. Largely discovered in the first half of the 20th century, this has been widely accepted as the modus operandi of <em>Nepenthes</em> pitcher traps.</p>
<p>But in early 2003, a young German PhD student was caught in a tropical downpour while observing a trail of ants running across a <em>Nepenthes bicalcarata</em> pitcher in the peat swamp forests of Brunei, North Borneo. The ants were collecting nectar from the collar-like upper rim of the pitcher, known as the peristome - a structure thought to purely serve prey attraction. As soon as the rain started, the ants suddenly <a href="http://www.pnas.org/content/101/39/14138.long">started to slip</a> on the peristome, and dozens of them ended as prey in the pitcher. Unlike most other plant surfaces, the peristome is highly wettable. Water droplets spread across the surface and form a continuous thin film on which insects hydroplane like a car tyre on a wet road. The effect is so striking that it has inspired engineers to design artificial <a href="Bioinspired%20self-repairing%20slippery%20surfaces%20with%20pressure-stable%20omniphobicity">anti-adhesive surfaces</a> based on it.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/FHW-T0TeNzw?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Danger: slippery when wet. Source: Holger F. Bohn.</span></figcaption>
</figure>
<p>The past ten years have seen an unprecedented boom of scientific interest in pitcher plants, leading to the description of a staggering 38 new species and the discovery of further astonishing trapping mechanisms.</p>
<p>One of the strangest strategies has been described for <em>Nepenthes gracilis</em>, which uses the <a href="http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0038951">impact of falling rain drops</a> to catapult prey into the trap, or captures insects seeking shelter from the elements under the pitcher lid. Other species have given up carnivory entirely and instead engage in a mutual relationship with <a href="http://rsbl.royalsocietypublishing.org/content/5/5/632.full">tree shrews</a> or <a href="http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0021114">mountain rats</a>.</p>
<figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/26460/original/fwg3sgdd-1372437384.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/26460/original/fwg3sgdd-1372437384.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=698&fit=crop&dpr=1 600w, https://images.theconversation.com/files/26460/original/fwg3sgdd-1372437384.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=698&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/26460/original/fwg3sgdd-1372437384.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=698&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/26460/original/fwg3sgdd-1372437384.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=877&fit=crop&dpr=1 754w, https://images.theconversation.com/files/26460/original/fwg3sgdd-1372437384.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=877&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/26460/original/fwg3sgdd-1372437384.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=877&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Caught short: a tree shrew snacks at a <em>Nepenthes lowii</em> and relieves himself - providing a nitrogen-rich meal for the plant.</span>
<span class="attribution"><span class="source">Ulrike Bauer</span></span>
</figcaption>
</figure>
<p>Here, in these so-called “tree shrew lavatories”, the plant offers sugary secretions to the mammal which in turn leaves its excrements in the pitcher, fertilising the plant with precious nitrogen. Similarly, <em>Nepenthes hemsleyana</em> benefits from the faeces of <a href="http://rsbl.royalsocietypublishing.org/content/7/3/436">tiny woolly bats</a> (<em>Kerivoula hardwickii</em>) that roost inside the pitchers.</p>
<p>Maybe the most remarkable case of mutualism, however, is found in <em>Nepenthes bicalcarata</em>: the pitchers of this bizarre plant are inhabited by a <a href="http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=5258192">specially adapted ant species</a> (<em>Camponotus schmitzi</em>) which can not only negotiate the wet peristome with ease but also <a href="http://www.ncbi.nlm.nih.gov/pubmed/22526112">swim and dive</a> in the pitcher fluid, hunting for aquatic mosquito and fly larvae. </p>
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<img alt="" src="https://images.theconversation.com/files/26461/original/h9bqr26f-1372437999.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/26461/original/h9bqr26f-1372437999.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=666&fit=crop&dpr=1 600w, https://images.theconversation.com/files/26461/original/h9bqr26f-1372437999.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=666&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/26461/original/h9bqr26f-1372437999.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=666&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/26461/original/h9bqr26f-1372437999.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=837&fit=crop&dpr=1 754w, https://images.theconversation.com/files/26461/original/h9bqr26f-1372437999.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=837&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/26461/original/h9bqr26f-1372437999.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=837&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"><em>Nepenthes bicalcarata</em>, the only known example of a carnivorous plant inside which a species of ant exclusively lives and hunts for food, residing in leaves specially adapted for them. The ants even drag large prey items out from the pitcher to eat (see inset).</span>
<span class="attribution"><span class="source">Ulrike Bauer</span></span>
</figcaption>
</figure>
<p>By killing the larvae that feed from the same nutrient bounty that would feed the plant, the ants <a href="http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0063556">reduce the loss of nutrients</a> to the plants. The ants also <a href="http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2435.2011.01937.x/abstract">clean the peristome</a> which keeps it slippery, and protect the developing pitcher buds by aggressively attacking particular <a href="http://www.gtoe.de/PDF/Ecotropica_2007_01/Merbach%20et%20al%202007,%20Ecotropica%2013-1.pdf">herbivorous weevils</a> trying to dine on them. The plant, in turn, offers nesting space for the ants in specialised hollow tendrils.</p>
<p>The biology of most of the 140 currently described <em>Nepenthes</em> species is still virtually unstudied, with many more astonishing secrets likely to be discovered. Sadly, the rapid progress of land development poses a serious threat to many lowland species as their natural habitats get converted into plantations, settlements and industrial parks. Mountain species are less threatened by habitat loss but instead suffer from poaching for local horticultural markets, and from a warming climate from which there is no escape.</p>
<p>Their incredibly sophisticated adaptations have enabled pitcher plants to survive in some of the most hostile and nutrient-deficient environments such as poisonous soils, acidic peat bogs and even sheer rock faces. But in the face of bulldozers and man-made forest fires, they are fully at our mercy.</p><img src="https://counter.theconversation.com/content/15607/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Dr Ulrike Bauer receives funding from the Cambridge Philosophical Society. She is a Fellow of Robinson College Cambridge and works at the Department of Plant Sciences, University of Cambridge. She is also a Research Associate with Universiti Brunei Darussalam where she has conducted her field research on Nepenthes pitcher plants since 2005.</span></em></p>Ever since their discovery, carnivorous plants have fascinated scientists and spurred the imagination of artists, writers and filmmakers. While the Puya chilensis cactus at the Royal Horticultural Society…Ulrike Bauer, Henslow Research Fellow, University of CambridgeLicensed as Creative Commons – attribution, no derivatives.