What makes a spider spin a web?

If you have ever watched a spider as it works to build a web, spiralling inwards with a thread of silk, that intersects each glistening spoke with a precise touch of the foot, you will know that it is a remarkably complex behaviour. In this episode, presenter Geoff Marsh dives into the minds of spider-constructors as they build their webs. CrowdScience listener Daan asked us to find out how spiders can build webs without ever being taught how to do it. Are they just little robots controlled entirely by their genetic instructions? Spider silk expert Dr Beth Mortimer, describes the process of building a web in detail, while Professor Iain Couzin explains the simple modular behaviours that build up, in sequence, to create apparently complex instincts, like the huge locust swarms that are sweeping across vast areas of Africa and Arabia. Taking us deep under the exoskeletons of invertebrates, Professor Gene Robinson reveals an animal's behaviours can be altered by their genes, and the root similarity between learning and instincts. Spiders, despite their tiny size, have fascinating behaviours. Some jumping spiders can work out the best way out of a maze, and one arachnologist reveals how some social spiders can cooperate to build communal webs and capture moths that are many times their size. Geoff searches for the science that can reveal how instinct can create complex behaviour by setting up interviews at the homes of spider experts from around the world. Presented by Geoff Marsh. Produced by Rory Galloway for BBC World Service.Image: European garden spider, Araneus diadematus hanging in the web. Photo by: Michael Siluk / Universal Images Group via Getty Images