Most spiders only eject silk from glands in their rear ends but Scytodes—the spitting spider—is an exception. It can also shoot silk from its mouthpart. It does so with great force, and it impregnates these strands with venom to create a sticky gum that both poisons and traps its victims. It’s the closest natural equivalent to Spider-Man’s web-shooters.

If the prospect of a spider with a long-range weapon freaks you out, you are not alone. Even other spiders are wary of Scytodes.

In the Philippines, the spitting spider will readily attack jumping spiders and its web is often littered with arachnid carcasses. Ximena Nelson and Robert Jackson from the University of Canterbury have shown that it often targets a black-and-lemon species called Phintella piatensis. Scytodes will build its nest directly over a Phintella nest and ensnare the jumping spider as it enters and leaves its home. Sometimes, it even taps on the nest with its legs, perhaps to check if anyone’s home.

But Phintella is not entirely defenceless. Nelson and Jackson also found that it protects itself by nesting in the company of the weaver ant Oecophylla smaragdina.

When the duo placed leaves with Phintella nests in a chamber, and wafted in the smell of weaver ants, they found that Scytodes avoided building its own web overhead. And Phintella, in turn, was more likely to build nests on leaves where the ants could be seen or smelled.

View Images Weaver ant kills Phintella. Credit: Robert Jackson

The reason is simple: the ants are voracious predators and spiders are on their menu. They’re so aggressive that farmers often deliberately use them to protect mango crops from pests. Even Scytodes’ trademark weapon is of little use: its spit will immobilise a couple of weaver ants, but it can’t pin down an entire group. When Nelson and Jackson housed a Scytodes with weaver ants, it was almost always killed.

Phintella, however, isn’t bothered by the weavers. It fashions a silken cocoon like most jumping spiders do, but it uses an especially tough and dense weave that the ants cannot tear open. It also builds doors! It has hinged silken flaps at either end of its nest which seal it away when it’s inside the nest, and which the ants rarely try to open. The ants do sometimes capture Phintella, as the image above shows, but this is relatively rare.

So, its ant-proof home allows Phintella to surreptitiously recruit the weavers as protectors, without succumbing to them itself. It’s like a person who seeks safety by walking into the most dangerous part of town in a Kevlar suit.

There are many cases where ants act as bodyguards for other species, including aphids, acacia trees, and some butterflies, in exchange for food and nutrients. But the relationship between Phintella and the weavers isn’t a mutualism, where both partners benefit. The ants don’t seem to get anything from Phintella’s presence. They don’t suffer either, so it’s not parasitism. Instead, Phintella is more of a commensal—a creature that benefits by living alongside another, without offering any advantages in return.

It’s also not the only jumping spider to have a connection with ants. Some eat them. Others mimic them to a spectacular degree. One mimics ants to avoid being eaten by spiders so that it itself can eat spiders. And Phintella, which neither looks like an ant nor eats them, lives alongside ants and avoids being eaten by them so it can also avoid being eaten by another type of spider, which ants can eat. Ain’t nature grand?

Reference: Nelson & Jackson. 2014. Timid spider uses odor and visual cues to actively select protected nesting sites near ants. Behav Ecol Sociobiol. http://dx.doi.org/10.1007/s00265-014-1690-2