Species

Spider Hunting Spider: Portia and the Art of Problem Solving

A peanut-sized jumping spider called Portia concocts complex strategies to catch its prey

By Samuel John

Nearly 48,000+ species of spiders share this Earth with us. And just like humans have adapted through many millennia to a variety of habitats, spiders have too, over a few million years. We have spiders that are fishers, desert-dwellers, mountaineers, and even strategists. It is this last category of spiders, of the genus Portia (pronounced “porsh-a”, like the automotive brand Porsche) that causes much bewilderment. The idea of strategic thinking in an animal with a brain that can fit on the head of a pin is just as fascinating as it sounds.

Closely observing jumping spiders challenges our common perceptions of spiders. Aside from their puppy-dog-eyes, jumping spiders display a variety of behaviours that will fascinate anybody willing to look past the many misguided prejudices that surround spiders. In Japan, Toxeus magnus, a species of jumping spider, nurtures its young with a milk-like substance, in a process that resembles lactation in mammals. In Australia, the popular peacock spider dances waves of electric colour into the hearts of potential mates. Spread through tropical Africa, Australia, and Asia (including India) Portia is a genus of spiders that problem-solves better than most MBA graduates I’ve had the pleasure of working with.

Spiders in the genus Cosmophasis are spectacularly coloured. This spider is looking for a weaver ant’s nest. Photo: Samuel John </br> A Portia sp. out on a hunt. Spiders in the genus Portia are araneophagic, meaning they primarily prey on other spiders. Cover Photo: Sara

Spiders in the genus Cosmophasis are spectacularly coloured. This spider is looking for a weaver ant’s nest. Photo: Samuel John
A Portia sp. out on a hunt. Spiders in the genus Portia are araneophagic, meaning they primarily prey on other spiders. Cover Photo: Sara

You are what you eat

With the exception of one jumping spider, all spiders are exclusively predatory. Each species of spider hunts specific sets of prey with the adapted precision that only nature could engineer. Imagine a tiny little jumping spider that feeds primarily on other spiders. With the ability to think, plan, and learn. Spiders in the genus Portia have been observed carefully planning the best possible approach to a potential target, executing the plan, and learning through trial and error.

Picture yourself being given a complex puzzle each morning, with a reward for solving it in time. Solve it and you get a scrumptious breakfast, fail and you will likely be eaten up. A typical day out on a hunt with a Portia could go from stealthily stalking another jumping spider to venturing onto the web of an orb-weaving spider. Both dangerous pursuits, as Portia’s target prey is capable of turning the prey-predator table and becoming the hunter. Having to survive such dangerous circumstances to get every single meal is the likely reason why Portia has evolved into a master of strategy.

Gasteracantha is a genus of orb-weaver which can be easily distinguished by its signature abdominal spikes. This one is seen resting after a satisfying afternoon meal. Photo: Samuel John

The path of least resistance

The most efficient path to a target may not always be the shortest. When you have the privilege of watching a Portia hunt in the wild, you will see what appears to be a tiny ball of debris with incredible camouflage moving through the forest on eight legs. Portia moves slowly and rhythmically until it has a web and its resident spider in sight. It will then proceed to briefly take your breath away, as a spider no larger than a thumbnail, stops to think before it acts (a lesson we could all learn from). The brief moment of pause is time spent plotting the best route of access towards potential prey that is both larger than it, and has the home-side advantage of sitting on its own web.
On a typical day, Portia will choose one of two broader strategies of entering the prey spider’s space — bypassing the web and/or directly entering the web. This is followed by tactical decision-making that is driven by trial and error.

The first strategy will take the little spider on a detour. This path will likely be a longer route that momentarily moves further away from its target. For a few brief moments Portia may even lose sight of its prey. The spider courses through hollow trees, branches and leaves to get to a point directly above the web of its unsuspecting victim. Portia’s potential victim in this case, an orb-weaver spider, experiences the world through vibrations and consequently does not have very good eyesight. Fully aware of its victim’s strengths and weaknesses, Portia sets a silk dragline on a point directly above the web and goes on to recreate the famous scene from the movie Mission Impossible. It carefully descends until it is just a few millimetres away from its target — and then little Portia strikes! This mode of hunting requires Portia to recognise potential prey and then rationalise the advantages of not moving directly towards its prey. It requires the little spider to understand that its chances of success are much greater when the victim’s natural advantage of sitting on its own web are removed.

The Art of War
What happens when a Portia comes across a spider on a web with no apparent structural aides for a controlled aerial descent (no branches, leaves, or structures above the web)? Portia’s orb-weaving target is highly sensitive to vibrations on its web and is programmed to distinguish between a meal, debris, and a potential threat. To circumvent the orb-weaver’s natural strength, Portia’s method seems to mirror the advice of one of history’s greatest military strategists Sun Tzu in his famous treatise.

“All warfare is based on deception. Hence, when we are unable to attack, we must seem unable; when using our forces, we must appear inactive; when we are near, we must make the enemy believe we are far away; when far way, we must make him believe we are near” – Sun Tzu in the The Art of War

An orb-weaver spider feeds on a midnight snack. Orb-weavers can be found everywhere from dense forests to home gardens. Photo: Samuel John

An orb-weaver spider feeds on a midnight snack. Orb-weavers can be found everywhere from dense forests to home gardens. Photo: Samuel John

The little spider first carefully ventures onto the edge of the orb-weaver’s web without alerting the resident spider. Once it has found a satisfactory spot, it begins to slowly pluck at the web with one leg, then another, then with its pedipalps. In a process that could take hours and a seemingly unlimited combination of plucking with different legs and appendages, Portia eventually stumbles upon a combination that piques the orb-weaver’s curiosity. As the unsuspecting victim comes to inspect this strange set of vibrations, Portia strikes! Sinking its fangs into its victim, it envenomates its next meal.

A Portia sp. sinking its fangs into its victim at the edge of the victim’s web. Photo: Sara

If Portia doesn’t succeed on its first try through either of these methods, and has not been wounded severely in the attempt, it will go back and try again, constantly learning from previous attempts.

Now you see me, now you don’t
Portia’s potential prey is not limited to web-building spiders and extends to fellow jumping spiders as well. The widely diverse family of jumping spiders has one strength in common: excellent daytime vision. In typical Portia style, this elite little strategist has found a way to turn its prey’s strength into a potential weakness.

When a Portia picks up on chemical signals of another jumping spider Jacksonoides queenslandicus, it speculates that the spider is nearby even if it can’t see its victim. In the presence of these chemical signals, Portia takes a break from its usually waddling walk to make a seemingly random leap. Jacksonoides queenslandicus with its sharp eyesight turns briefly to look at this sudden movement, breaking its camouflage and revealing its position to Portia. Portia will then wait for the Jacksonoides queenslandicus to turn away, and then begin the slow and steady process of stalking it. Once it is close enough, Portia strikes!

Using a combination of the behaviours described above, little Portia also preys on the females of the genus Euryattus sp., by mimicking the mating signals used by the males of this genus.

Fish climbing ladders
Over the past century, there has been a growing sense of appreciation for the intelligence prevalent outside our own species (with the caveat that indigenous communities were well ahead of us by a few centuries in this regard). It is heartening to hear stories of us discovering self-awareness in elephants and the mathematical abilities of a raven, but we must remember that our concepts of intelligence are bound by the limits of our own senses and perception. The definition of intelligence would change in ways we cannot yet imagine when considering some actions in the natural world: ballooning spiders studying electric currents and the wind with the hair on their legs; the speed and logistical efficacy with which ants mobilise a piece of food out of our kitchens and back to their colony; or a tiny jumping spider that concocts complex strategies to hunt.

Whether you’re out on a stroll through the park, on a jungle safari, or planning your next research study, maintain a rational amount of open-mindedness while interacting with the environment — it could lead to many meaningful and enriching experiences with our natural world.

A jumping spider stalking its prey, takes a brief moment to inspect the photographer. While a lot of work has recognised the intelligence of Portia, there is a great deal yet to be understood about other genera of jumping spiders. Photo; Samuel John

Samuel John

is an ex-corporate zombie who found the answers to life, the universe, and everything, on a spider's web. He can be seen at times playing the blues for his eight-legged audiences.

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