What Plants Do Spiders Eat?

How spiders can harm and help flowering plants

Interactions between organisms such as plants and animals can be found everywhere in nature. Anina Knauer and Florian Schiestl, a professor at the Department of Systematic and Evolutionary Botany of the University of Zurich, have taken a closer look at one such instance: the interaction between crab spiders and the buckler-mustard, a yellow flowering plant common in Europe.

The harmful side of crab spiders

Crab spiders are predators that lie in wait for their prey on the flowers. It used to be assumed that these spiders harm the plant, because they catch pollinating insects or discourage them from visiting the flowers. The ecologists at UZH have now been able to reveal a surprising phenomenon: «Crab spiders find the plant by following the scent of its flowers. They do so using ?-ocimene, the floral volatile that also attracts bees,» says Schiestl.

Floral volatile serves as a cry for help

Indeed if crab spiders are sitting on the flowers, fewer bees will visit because they’re discouraged by the spiders. But the spiders don’t just eat pollinators. They also eliminate plant-eating insects and their larvae that feed on the flowers or fruit and damage the plant. This way the crab spiders benefit the plant, bearing out the principle that the enemy of my enemy is my friend. Apparently the benefit is so great that when attacked by florivores, the plants give off larger amounts of the floral volatile that attracts the spiders. This «cry for help» actually works: in response to it the spiders are increasingly likely to visit the flowers that are being attacked, where they find rich pickings.

Understanding interactions to protect ecosystems

The study shows that the effect of interacting organisms is highly dependent on the ecological context. But in complex ecosystems the consequences can’t always be predicted. This means that the disappearance of existing interacting partners or the appearance of new ones can have unforeseeable implications for individual members of an ecosystem. «For this reason it’s important to better understand the interactions between organisms and their consequences to be able to apply the insights in the protection of ecosystems or organic farming,» concludes Florian Schiestl.

Story Source:

Materials provided by University of Zurich. Note: Content may be edited for style and length.

Journal Reference:

  1. Anina C. Knauer, Moe Bakhtiari, Florian P. Schiestl. Crab spiders impact floral-signal evolution indirectly through removal of florivores. Nature Communications, 2018; 9 (1) DOI: 10.1038/s41467-018-03792-x

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These Spiders Like Some Greens with Their Insects

Spiders are known as clever predators, trapping and stalking their insect prey. But many species round out their diets with a little roughage.

There are at least 95 recorded instances of spiders eating plant products, according to a new review in the Journal of Arachnology. Spiders chow down on everything from nectar to sap to small fruiting bodies, wrote the study’s leader, Martin Nyffeler, a research fellow in conservation biology at the University of Basel in Switzerland, and colleagues.

«Such a large diversity of plant types, plant taxa and plant materials being used as food by spiders is novel,» Nyffeler told Live Science.

Even the most plant-loving spiders can’t survive on a vegetarian diet alone, the researchers wrote, but spiders might be more resilient in times of food shortages if they eat plant food as well as prey. [See Photos of Amazing Plant-Eating Spiders from Around the World]

Plant food

About 60 percent of reported incidents of spiders eating plants have been jumping spiders (Salticidae), the largest family of spiders. These spiders live all over the world, and their plant-eating behavior has been observed on every continent except for Antarctica (where the spiders don’t live) and Europe (where they live but haven’t shown their habit of eating leafy greens). In about 75 percent of reported cases, spiders were observed eating nectar, and field tests of spiders have found that 20 percent to 30 percent have fructose in their guts — an ingredient in nectar — the researchers wrote.

For some jumping spiders, getting nectar is a sticky business, Nyffeler wrote in another study published March 6 in the journal Peckhamia. Ants also eat nectar, so spiders have to scurry in when ants aren’t present in order to get nectar without a battle. They may also have to outrun or outjump ants if challenged, Nyffeler said. One genus, Peckhamia, even mimics ant behavior to sneak in for a sweet treat.

Nectar is only one portion of the potential spider diet, though. Some spiders bite into leaves to feed on plant sap. The South American spider Anelosimus rupununi has been seen biting into mango leaves in Venezuela to suck the sap, for example. Spiders even eat the solid parts of the plants — though they have to inject small pieces with digestive fluids to liquefy them, just as they do with insects. In particular, a colorful jumping spider from Central America, called Bagheera kiplingi, eats almost exclusively Beltian bodies, which are sugar-rich nubs that grow on acacia plants.

A juvenile jumping spider (Baheera kiplingi) eating a Beltian body, or a detachable leaflet tip from an acacia tree, in Akumal Mexico. Beltian. (Image credit: Eric J. Scully, Harvard University)

Even weirder, some spiders feed on honeydew, which is a sugary liquid secreted by insects such as aphids that are also feeding on plants. Two species of jumping spiders, Myrmarachne foenisex and Myrmarachne melanotarsa, have been seen «milking» honeydew from insects called coccids. [Check Out Incredible Photos of Peacock Spiders]

Spiders seem to have all the enzymes they need to break down plant material, the researchers wrote, except for exinase, which breaks down the outer covering of pollen. But some spiders have been seen eating pollen, perhaps by piercing its outer shell. Spiders may also consume pollen, seeds and spores that accidentally get captured in their webs, the researchers wrote.

See also:  When Spider Bites What Happens?

A balanced diet

About 80 percent of spider plant-eating occurs in warmer regions of the world, perhaps because plants secrete more nectar in warmer spots, Nyffeler and his colleagues wrote. They found evidence of more than 60 plant-eating spider species, but many more species may do the same, they added.

Most spiders cannot survive on plants alone, Nyffeler said. In lab studies, scientists have fed spiders vegetarian diets, like pollen or nectar alone, and have found that the spiders fail to molt or they have stunted growth. A possible exception is the largely herbivorous species B. kiplingi, Nyffeler said. But one laboratory study found that when B. kiplingi spiders were fed only plant matter, they died after a few weeks, too.

Nevertheless, plants may be an important part of the spider diet, Nyffeler said.

«The ability of spiders to derive nutrients from plant materials is broadening the food base of these animals; this might be one of several survival mechanisms helping spiders to stay alive for a while during periods when insect prey is scarce,» he wrote in an email to Live Science. «Furthermore, enriching the spiders’ diets with plant materials leads to a more diverse diet, a process considered to be advantageous from a nutritional point of view, since diet mixing is optimizing a balanced nutrient intake.»

More studies need to be done to understand how different categories of plant food contribute to spider diets, how spiders digest plant foods and how frequent plant-eating is under natural conditions, Nyffeler said.

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Spider Snacks: Photos of Plant-Eating Arachnids

Herbivorous spider

(Image credit: Copyright Robert L. Curry, Villanova University)

Spiders are known as cunning predators, but a new review in the Journal of Arachnology finds that many round out their diets with a side of vegetables. There are at least 95 reports of spiders eating plant matter, from nectar to sap to pollen, University of Basel lecturer Martin Nyffeler and colleagues reported in the paper.

One spider, a jumping spider species called Bagheera kiplingi, has a mostly herbivorous diet. Seen here, a female feeds on the fatty, protein-rich Beltian bodies of the acacia plant. These structures are part of the plant’s strategy to attract ants, which protect the plants against herbivores. But spiders have found a way to muscle in on the free food, too.

(These photos are from Martin Nyffeler’s article «Phytophagy in jumping spiders: The vegetarian side of a group of insectivorous predators» http://peckhamia.com/peckhamia/PECKHAMIA_137.1.pdf)

Sweet Treat

(Image credit: Copyright David E. Hill, Peckham Society, Simpsonville, South Carolina)

The majority (about 75 percent) of reports of spiders eating plant products involve nectar consumption. Here, a male jumping spider (Sassacus papenhoei) eats from a nectar-secreting gland in South Carolina.

Competition for food

(Image credit: Copyright David E. Hill, Peckham Society, Simpsonville, South Carolina)

Seeking out nectar can put spiders in direct competition with ants, which also rely on the energy-rich liquid from plants. Ants are defensive of nectaries, so spiders usually watch and wait for the ants to leave before scuttling in to drink nectar themselves. This male jumping spider (Sassacus papenhoei) waited until this ant left to drink from the same nectary. [Read more about vegetarian spiders]

See also:  What Kind Of Spider Looks Like A Crab?

Waiting for a turn

(Image credit: Copyright David E. Hill, Peckham Society, Simpsonville, South Carolina)

A female jumping spider (Tutelina elegans) normally eats ants. But in this image, she waits patiently as an ant drinks from a plant nectar gland, or nectary. Jumping spiders have strong vision and avoid their ant competitors by sight. If a confrontation ensues, the spiders typically out-run or out-jump the ants.

Sipping something sweet

(Image credit: Copyright David E. Hill, Peckham Society, Simpsonville, South Carolina)

A female jumping spider of the genus Peckhamia drinks from a nectary on a shrub of the genus Prunus, a group the includes plums, almonds and chokecherry. Spiders may spend anywhere from a few seconds to a few minutes sucking nectar from these plant structures. Peckhamia spiders look and act like ants, which makes it easier for them to slip into ant-guarded nectaries for a snack.

The confrontation

(Image credit: Copyright Andrea Lim, James Cook University)

A colorful Cosmophasis micarioides jumping spider watches and waits for an opportunity as golden-tailed spiny ants feed at a plant nectary near Cairns, Australia. The spider dashes forward to sneak a sip of nectar whenever the ants move aside.

Midnight snacks

(Image credit: Copyright Woodbridge Foster, Ohio State University)

Jumping spiders aren’t the only nectar-imbibing arachnids. Some nocturnal running spiders, like this Hibana velox in Vero Beach, Florida, also drink from plant nectaries. This spider is drinking nectar from a castor bean plant. «In their search for nectar, these spiders wander over plants and stop for a while each time they have approached a nectary,» according to Nyfffeler. «The spiders then press their mouthparts into the nectary opening imbibing nectar, which may last from a few seconds up to a few minutes.»

Sipping sap

(Image credit: Copyright David E. Hill, Peckham Society, Simpsonville, South Carolina)

Some spiders don’t just drink nectar; they also seek out plant sap. The female jumping spider Pelegrina galathea bites into a leaf and sucks down the sap that oozes out. This picture was taken indoors.

Biting spiders

(Image credit: Copyright David E. Hill, Peckham Society, Simpsonville, South Carolina)

An indoor shot of the female jumping spider Hentzia milrata drinking plant sap. Spiders can’t digest solids, but they can bite through leaves to get to the liquid food inside.

Pollen studded

(Image credit: Copyright Nick Hobgood, University of the South Pacific)

Another plant food some spiders enjoy is pollen. Research suggests spiders lack the enzyme to digest pollen’s outer shell, but they can pierce the pollen with their fangs and inject digestive juices to soften up the inside, just as they might with a fly or other insect. Here, a jumping spider of the species Plexippus is decorated with pollen at a home garden in Kinshasa, the Congo.

Web-caught pollen

(Image credit: Copyright Claudia Ludy, Heidelberg)

A female orb-weaver spider Araneus diadematus gets a consolation prize after a wild bee escapes her web: A packet of pollen left behind by the struggling insect. She digests and consumes it. This photo was taken near Munich, Germany, but most reports of spiders eating plant matter come from tropical and subtropical regions, where sap- and nectar-excreting plants are plentiful.

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