There are an estimated 50,000 species of spider living on Earth, from behemoths like the giant huntsman and goliath birdeater, down to the tiniest, the dwarf orb weaver and Patu digua. In this extract from “The Lives of Spiders: A Natural History of the World’s Spiders” (Princeton University Press, 2024), author Ximena Nelson looks at the three species with unusual diets — plants, blood and pill bugs.
Vegetarian spider
Scientific name: Bagheera kiplingi
Family: Salticidae
Body length: 1∕5–¼ in (5–6 mm)
Notable anatomy: Males have iridescent green markings on cephalothorax and abdomen
Memorable feature: Primarily vegetarian
A spider is an unlikely vegetarian, but Bagheera kiplingi almost fits the bill. Supplementing its diet with nectar, ant larvae, and nectar-feeding flies, this jumping spider feeds almost entirely on Beltian bodies, the detachable fat and protein-rich leaf tips of Vachellia acacia shrubs.
Bagheera is so dependent on Beltian bodies that it is an obligate resident of Vachellia plants, where it lives in areas that are not well patrolled by the resident Pseudomyrmex ants. There is such host specificity to the plant that the spider’s geographic range is limited by the presence of Vachellia.
Plant mutualisms
Ants can be helpful to plants because they tend to be aggressive and keep herbivorous insects away. Consequently, many plants make an effort to lure ants as bodyguards and keep them around by producing accessible nectar through extrafloral nectaries. This continuous source of food is irresistible to ants, but often is also exploited by spiders, especially wandering spiders that roam to hunt their prey.
This includes many species of jumping spiders, where nectarivory may be a common tactic to obtain a meal with less risk of injury than hunting. Nectarivory can increase spider longevity and reproductive output. Importantly, for the tiny spiderlings, nectar may provide much-needed energy that allows them to hunt prey inevitably larger than themselves. In addition to extrafloral nectar, Vachellia species produce nutritious Beltian bodies to keep Pseudomyrmex ants nearby.
Related: We now know why tarantulas are hairy — to stop army ants eating them alive
The defense put up by the ants is formidable, and few animals can encroach it. Bagheera…
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