Spiders' diets aren't limited to juicy insect bits; they've been shown to occasionally consume fish, frogs or even bats before -- but they spice up their menus with vegetarian courses too, zoologists from the US and UK have found.
Spiders are traditionally viewed as insectivorous predators, dining on anything their webs can trap. But scientists are becoming increasingly aware that's a skewed view of them, and that their diet is more diverse than we imagine. If available, spiders won't shy away from eating fish, frogs, bats -- all kinds of meat. But a team of zoologists from the University of Basel, Brandeis University and Cardiff University has now brought evidence of meat-eating spiders chowing down on plant-based foods too.
“The ability of spiders to derive nutrients from plants is broadening the food base of these animals; this might be a survival mechanism helping spiders to stay alive during periods when insects are scarce”, says lead author Martin Nyffeler from the University of Basel in Switzerland.
They gathered and documented all examples of spiders eating such items from scientific literature they could find. Their collection of data shows that spiders from ten families have been reported feeding on a wide range of plants such as trees, shrubs, ferns, flowers, weeds or grasses. And they aren't picky, either; they'll eat anything from nectar, sap or honeydew to leaves, pollen and seeds.
A family of diurnal spiders, the Salticidae, seem to be the most voracious plant-eaters of the Araneae order. These plant-dwelling, highly mobile foragers were attributed with almost 60 percent of the incidents documented in this study.
But such feeding habits aren't a Salticidae-only thing. Plant-eating in spiders has been reported from all continents except Antarctica, but seems to be more common in warmer areas of the globe. As a larger number of the reports relate to nectar consumption (which has its core distribution in warmer areas where plants secreting large amounts of nectar are widespread) this isn't too surprising.
“Diversifying their diet with plant is advantageous from a nutritional point of view, since diet mixing is optimizing nutrient intake,” Nyffeler concludes.
Currently, the extent to which different categories of plant-based food contribute to the spiders’ diet is still largely unexplored. But, as there currently is a known species of spider that is mostly herbivorous, the Central America indigenous Bagheera kiplingi, it can be assumed that in a pinch spiders can live on a full veggie diet for some time.
The full paper, titled "Plant-eating by spiders" has been published online in the Journal of Arachnology and can be read here.