Spiders eat insects. That’s why some of us are reluctant to kill the spiders we find in our homes. We figure they’ll eat the critters we really don’t want around. But a new study reveals that a spider’s diet can be far more diverse than what many of us learned in school. Many spiders, for instance, have a taste for plants.
Martin Nyffeler studies spiders at the University of Basel in Switzerland. He had seen scattered reports of plant-eating spiders in science journals for years. “I always found this topic very intriguing,” he says, “since I am a vegetarian myself.”
He and his colleagues have now combed books and journals for reports of spiders consuming plant material. There is only one species of spider known to be completely vegan: Bagheera kiplingi. This species of jumping spider lives in Mexico. It survives mostly on bits of acacia (Ah-KAY-shah) trees.
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Dozens of spider species, such as this Maevia inclemens jumping spider, may feed on plant parts, new research reveals.
While scientists have yet to find any other strict vegetarian spider, plant-eating by spiders now appears to be fairly common. A new study turned up evidence of veggie-eating among more than 60 species of them. They represent 10 taxonomic families and every continent but Antarctica.
Nyffeler’s group reports on spiders’ taste for greens in the April Journal of Arachnology.
Juicing it
Perhaps past scientists can be forgiven for overlooking this plant-eating behavior. That’s because spiders can’t eat solid food. They have a reputation for sucking the juices out of their prey. But that’s not quite the right description for what happens. A spider actually covers its prey with digestive juices. It then chews the meat with its chelicerae and sucks the juices in.
This eating style means that spiders can’t just cut a piece of leaf or fruit and chow down.
Some spiders feed on leaves by digesting them with enzymes prior to eating, much as they do with meat. Others pierce a leaf with their chelicerae, then suck out plant sap. Still others, such as Bagheera kiplingi, drink nectar from special tissues. Called nectaries, these tissues are found in flowers and other plant structures.
More than 30 species of jumping spiders are nectar feeders, the researchers found. Some spiders have been seen pushing their mouthparts deep into flowers to reach that nectar. This is similar to how some insects drink nectar.
And nectar slurping isn’t accidental behavior by those spiders. Some can feed on 60 to 80 flowers in an hour. “Spiders probably act sometimes unintentionally as pollinators,” Nyffeler says.
Pollen is probably another common plant-based food for spiders, especially those that make outdoor webs. That’s because spiders eat their old webs to recycle the proteins. And when they down those webs, they also eat anything that might be caught on the sticky strands, such as calorie-rich pollen. Spiders also might be consuming tiny seeds and fungal spores this way. Those spores, though, may be a risky meal. That’s because there are many fungi whose spores can kill spiders.
The researchers also found some cases of spiders intentionally eating pollen and seeds. And, they note, many spiders are eating plant material when they munch on plant-eating insects. But most spiders need at least a little meat to get all the nutrients they need.
“The ability of spiders to derive nutrients from plant materials is broadening the food base of these animals,” Nyffeler says. “This might be one of several survival mechanisms helping spiders to stay alive for a while during periods when insect prey is scarce.”