Jumping spiders

Article and images by Dr Julie O'Connor, senior conservation partnerships Officer, Sunshine Coast Council

You probably think there is nothing in your backyard that could match the hunting prowess of the planet’s big mammalian predators. Well, meet the jumping spiders (salticidae). They may be tiny but their capacity to stalk and capture prey is astounding.

Globally, Salticidae is the most abundant and diverse of all the spider families, with over 500 described genera and more than ten times as many described species. These spiders are small, very small, with the majority barely larger than a grain of rice. In fact, the largest known jumping spider on Earth, Hyllus gigantus, is still only 25mm long. Their small size and enchanting courtship behaviour has arguably made them the world’s most popular spiders. Well, let’s be honest – probably the world’s only popular spiders. The boost in their popularity may be largely due to peacock spider expert Jurgen Otto’s YouTube compilation of 51 different species dancing their way through their adorable courtship rituals.

One of the keys to the jumping spider’s hunting prowess is its visual acuity. This is due largely to a combination of the 2 structurally unique forward-facing eyes and another 6 laterally positioned eyes, which effectively endow the spider with both 3D and 360° vision. The 2 large forward facing eyes help the spider to judge distance using a unique defocusing technique. As humans, we judge distance by adjusting focal length of the eye’s lenses. Jumping spiders use a method of image defocus aided by special photo receptor layers in its principal eyes, which contain a green-sensitive pigment. The amount of foreground defocus under green light gives it excellent depth and distance perception. The 360° vision becomes obvious when you try to photograph a jumping spider, which even when approached from behind will often turn to face the photographer.

In addition to their exceptional eyesight, jumping spiders have another superpower. Some species can leap up to 40 times their own length, which is no mean feat for a spider only a few millimetres long. In fact it has been compared to a human leaping the length of a school bus without a run up. Some species achieve this by forcing blood at high pressure into their legs causing them to extend rapidly, virtually catapulting the spider forward. For others, the capacity to make the jump is directly related to the mass of their leg muscles. Whichever mechanism is used, this is no willy-nilly fling into the wild blue yonder. The combination of excellent vision and an enviable jumping ability will ensure the spider frequently meets its target prey. Two silk threads also help by stabilising its jump, and if the leap doesn’t quite go to plan, the threads can also serve as a safety line.

If the physical prowess of the Salticidae family has failed to impress you, consider this. A Queensland species, Portia fimbriata, which specialises in hunting other spiders, has been found to not only plan its attack, but also learn and adapt its strategies if necessary. If you are awed by the fact that a spider barely more than 6mm long is capable of such complex thinking, you might like to follow up on some of the fascinating research undertaken by Dr Robert Jackson from the University of Canterbury.

If you are still not inspired by these little spiders and Jurgen Otto’s uplifting 51-species compilation set to “Stayin Alive” has still left you with a trace of arachnophobia, the delightful Maratus speciosus “dancing” YouTube video to YMCA will definitely cure you.

References

• Attenborough, David. 2005. Life in the Undergrowth, BBC Books, London.
• Harland, Duane P., Jackson Robert R. and Macnab, Aynsley M. 1999. Distances at which jumping spiders (Araneae: Salticidae) distinguish between prey and conspecific rivals, Journal of the Zoological Society of London, 247 357-364.
• Jackson, R. R. and Blest, A. D. 1982. The biology of Portia fimbriata, a web-building jumping spider (Araneae, Salticidae) from Queensland: utilization of webs and predatory versatility, _Journal of Zoology_ 196 255-293.
• Nabawy, Mostafa R. A., Sivalingam, Girupakaran, Garwood, Russell J., Crowther, William J. and Sellers, William I. 2018. Energy and time optimal trajectories in exploratory jumps of the spider Phidippus regius. _Scientific Reports_ 8: 7142.