What is the world’s only known primarily-vegetarian spider?

Virtually all spiders are predators. They may hunt using various methods, but they all end up sucking the liquidized “innards” of their prey. If they do consume plants, it is very rarely, and often by accident.

However, in Latin America there lives a unique spider called Bagheera kiplingi (‘B. kiplingi’). It’s a jumping spider, and it shares the group’s large, acute eyes and prodigious leaping ability. It also has a trait that singles it out among all 40,000 species of spider ~ it’s primarily vegetarian. No other known species of omnivorous spider has such a markedly herbivorous diet.

The arachnid exploits a symbiotic relationship between ants and acacia trees. The trees use ants as bodyguards. In return, the ants are compensated with shelter inside hollow thorns, and food: specialized nutritious nodules (full of protein and fat) called “Beltian bodies”, which form at the tips of the trees’ leaves. The spiders have learned to steal these delicacies from the ants.

Feeding on Beltian bodies is worthwhile but far from straightforward, as the spiders must avoid the body-guarding ants. The spider’s strategy is stealth and evasion. It builds its nests at the tips of the oldest leaves, where ants rarely patrol. In addition, the spiders actively avoid ant guards, when they see them approaching. (Those big eyes come in handy.) If cornered, they will use their powerful legs to leap away. Sometimes, they are forced to resort to dropping to safety by using a line of silk.