Phytophagy in jumping spiders: The vegetarian side of a group of insectivorous predators

Jumping spiders (Salticidae), a group of predominantly insectivorous predators, occasionally supplement their insect prey by deriving nutrients from plant food (‘facultative phytophagy’). The aim of this paper is to give a brief overview of the plant eating activities of salticids based on the published literature. Plant-eating by salticids has been reported from all continents except Antarctica and Europe. With regard to Antarctica it must be said that salticid spiders are absent from there. The previous lack of observations from Europe, on the other hand, may be explained by the fact that plant-eating by salticids is typically found in the warmer areas of the globe (_ 40° latitude) and because most of Europe is located in colder climates (> 40° latitude), it comes as no big surprise that this type of feeding has not yet been detected in European salticids. In order to exploit plant food resources, salticid spiders have to overcome various hurdles. Firstly, plant products such as floral nectar and pollen, serving to attract pollinators, might be chemically protected to deter nectar robbers and pollen thieves. Defensive chemicals such as alkaloids and cardenolides, if ingested along with plant food, may alter the spiders’ behavior as has been demonstrated in laboratory experiments with non-salticid spiders. Whether such behavior-altering chemicals have also an effect on free-living salticid spiders, remains to be researched. Secondly, plant-derived foods such as extrafloral nectar, Beltian bodies or coccid honeydew are aggressively defended by ant bodyguards and spiders must break through the ant defenses in order to get access to these types of food. Salticids detect ants by sight and are able to actively avoid them in most cases. Another situation does occur when the approaching salticid is an ant-mimic perceived by ants as ant (e.g., genus Myrmarachne or Peckhamia); ant-mimicking salticids appear to have unhindered access to plant-derived foods such as extrafloral nectar or coccid honeydew. Thirdly, spiders (adapted to eat insect prey) might require some specific enzymes enabling them to chemically break down plant materials. Currently it seems to be well understood how spiders accomplish the digestion of liquid plant food, whereas the process of digesting solid plant tissue is not yet completely investigated. As in other predaceous arthropods, the ability of spiders to derive nutrients from plant materials is broadening these animals’ diet which may have survival value during periods of prey scarcity.