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Fishing spiders By Stacey DoornenbalThe red crab spider retainsa memory of the ant andplans how it’s going tocatch its prey.Dr Simon PollardMisumenops nepenthicola, the fishing spider.A tiny spider that fishes for its foodinside a carnivorous tropical planthas caused a stir among CanterburyUniversity’s spider experts.The small predator, with the long scientificname of Misumenops nepenthicola, isa 6mm–long red crab spider that livesinside the pitcher plants of Borneo. Theplants, which have evolved into efficientnectar-secreting insect traps, feed onthe decomposing bodies of insects thathave drowned in pools of fluid held in theplant’s jug-shaped leaves. But rather thanfalling victim to the plants’ sweet trap,Misumenops nepenthicola has developeda complex hunting strategy that takesadvantage of the plant’s deadly attractions— it goes fishing.This cunning predatory behaviour wasdiscovered by Dr Simon Pollard, AdjunctAssociate Professor in the School ofBiological Sciences, while he was in Borneoin March this year advising the BBC onthe filming of a segment about the crabspider for the jungle episode of the PlanetEarth series. The segment, which wasdue to screen in the United Kingdom inNovember, is based on an earlier study ofthe spider by Pollard in which he found thespider had extraordinary aquatic skills.“I was in Sarawak with Professor RobertJackson (Biological Sciences) in late 2000to look at jumping spiders. I’d been therebefore but had never looked inside thepitcher plants themselves. I had a lookand kept seeing these flashes of red andrealised I was looking at a small spiderjumping into the fluid,” he says.“I’d never seen anything like it before.”Pollard, who is also Curator of InvertebrateZoology at Canterbury Museum, returnedto Borneo in February 2003 to find outhow the spiders were managing to breatheunderwater, basing himself at the NationalUniversity of Singapore. He found thatMisumenops nepenthicola has a smallcurved pit on its stomach where it trapsan air bubble as it dives into the pitcherplant’s slimy fluid. The bubble is held inplace near the spider’s breathing holesby hundreds of small hairs which pushthe bubble against the opposite sidesof the pit. This allows the spider to stayunder water for up to 40 minutes whilehiding from predators, and is also handywhen the little hunter decides to ambushunsuspecting prey.With the help of the BBC’s special lensesand equipment, an excited Pollard wasable, for the first time in March this year,to watch the little spider in action. He saysit had long been thought that Misumenopsnepenthicola caught and ate insects asthey landed on the rim of the jug. But itnow seems that all the predatory actionactually takes place inside the jug and inthe pitcher plant’s fluid.“Mosquito larvae live in the fluid in pitcherplants and they have to come to thesurface to breathe. These spiders pick uptheir vibrations and go after them. Theyrush down and grab them out of the water,or dangle their legs in the liquid and scoopthem up, or go into the water to grabthem,” says Pollard.“But what’s most interesting is that atthe bottom of the pitcher are dead bugs— an insect graveyard — and the spidernormally goes under the bugs to hide frompredators, but when it’s fishing it tossesthose carcasses up. It has a spider tantrumand throws its legs around flushing out thelarvae before grabbing them.”The spider also steals food from itshost, letting the pitcher plant deal withdifficult prey.“One of the most common things aboutpitcher plants is that the victims are mainlyants, often green weaver ants. But they’requite aggressive and far too dangerous fora crab spider to take on. So what the spiderdoes is get the plant trap to kill ants for it,”he says.The spider picks up vibrations from afalling ant as it hits the surface of thepitcher fluid and will watch as the antstruggles to get out. Waiting for about 10minutes after the ant has sunk, the spiderdives in and hauls the body out, clasped inits spiked legs and using web safety linesattached to the sides of the pitcher forextra support.“It’s fascinating to watch because it showsthe spider is retaining a memory of the antand planning how it’s going to catch itsprey. It is like the ant is out of sight but notout of mind.”A more detailed study of the crab spider ison the cards, with Pollard keen to find outwhat makes the spiders’ “dust speck of abrain” tick.“This is just the beginning of what could bea fascinating project.”Summer 2006 13