Beneficial insects

Spiders: Brainier Than Other Bugs

The common house spider (Achaearanea tepidariorum), found all over the world, keeps insects from taking over our homes. Photo: Fyn Kynd,

Before you tear out that web in your garden or squish the spider on your living room ceiling, do remember that spiders are beneficial to gardeners, eating insect pests and thus keeping your plants healthier. And, it turns out, they are surprisingly intelligent, the Einsteins of the arthropod world, largely due to their huge brains. 

The brain of adult humans only makes up about 2 to 3 percent of our body weight. In some spiders, especially the smallest ones, it can make up almost 80 percent of their total body cavity, spreading into their legs. 

Little spiders need big brains to build their complex webs and, in the case of spiders that feed by hunting, to track and surprise their prey. Hunting spiders can easily find their way through complex obstacle courses, putting rats to shame. This imitates how, in real life, they plan out intricate routes and detours to reach their quarry. Plus, web makers fine-tune their web, adjusting the strands like a piano tuner, so they vibrate just the right way. Some spiders also have excellent vision, akin to that of mammals and birds, much better than most insects, and it likely takes intelligence to coordinate the images captured by their (usually) eight eyes.

Why not turn that brain power to your advantage by letting spiders live, both among your houseplants and in your garden? Who knows, maybe you can start a conversation with one!

Garden writer and blogger, author of 65 gardening books, lecturer and communicator, the Laidback Gardener, Larry Hodgson, passed away in October 2022. Known for his great generosity, his thoroughness and his sense of humor, he reached several generations of amateur and professional gardeners over his 40-year career. Thanks to his son, Mathieu Hodgson, and a team of contributors, will continue its mission of demystifying gardening and making it more accessible to all.

7 comments on “Spiders: Brainier Than Other Bugs

  1. Look up Portia, the spider that eats other spiders: it is the subject of considerable interest among programmers who study biology.

    The short version is that planning an attack run on the prey – a three-dimensional route map which hides Portia from the target until the last moment – is too large a computation to fit into Portia’s tiny processor space.

    So Portia sits, and watches, and breaks up each candidate attack run into successive ‘slices’ of calculation, and runs them sequentially, storing the results. This is actually single-processor parallelisation – Portia doesn’t have a multi-core CPU or a Grid server in the basement, but a single-threaded CPU can still perform a ‘parallel’ calculation by time-slicing and parking the results.

    Portia sit, and watches, and calculates for a long time: sometimes over an hour. Clearly, a lot of those attack-run scenarios come up with “Nope, that route doesn’t work”.

    But one of them will, most times, and Portia is *fast*: there’s no ‘thinking about it’, and no complex “this way, that way” decisions; Portia *knows*.

    It will come as no surprise to hear that other spiders are terrified of Portia: playing a recording of the high-pitched whistles and pips they make will clear the area.

  2. Margaret

    Any creature that eats mosquitos is my friend.

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