Unusual Spider Webs

Peter Style explains why there is more to Spiders than we think

Arachnophobia is one of the most common fears among people, but if you take a minute to observe the complexity of spider’s webs, it does not take long to realise how much variation there is within the arachnid world and how much more there is to these creatures. Spiders have evolved to produce many different structures of web, each designed with the same function: allowing the spider to catch its prey.

To start with, not all spiders produce webs with the famous sticky glue droplets on them. Webs without glue are called cribellate webs. Spiders that produce these webs are able to produce silk as fine as 0.02 micrometres in diameter using their abdomen muscles. The silk is wound into interconnecting clumps called ‘hackle beads’, which are then laid over an area on the ground. When prey stumbles into the web mesh, it becomes easily entangled as it is so thin. The more the prey struggles, the more web it pulls towards itself, and so the more it becomes trapped and unable to move. This gives the spider time to bite and paralyse the prey with the toxins in its venom. The main reason this style of web has evolved is that the glue on webs degenerates quickly, so cribellate webs do not need to be replaced very often, saving the spider a lot of vital energy. Another advantage is that the spider is able to cover a wider area of land with its web network, greatly increasing its chance of ensnaring prey.

A second type of web is the horizontal sheet web, created by the Linyphiidae family of spiders. These are convex shaped with vertical silk threads stretching up above the sheet and connected to a support such as a leaf. These vertical threads, again without glue droplets, act as tripping lines for insects. The Linyphiidae spider hangs beneath the horizontal sheet web and waits for the insect to fall onto it, acting like a net, after the insect has been tripped by the vertical threads above. It then bites through the web to get to its prey, eating and digesting it, before then going on to repair the damage so it can effectively be used again.

Yet another type of web is the Ecribellate web, which is sticky in nature, due to glue droplets being present on the silk that forms them. One interesting example of an ecribellate web is that made by the family of Theridiidae spiders. These are particularly interesting because they have almost exactly the same structure as the Linphiidae spiders, described above, but reversed. So, instead of having the vertical silk threads above the horizontal sheet web, Theridiidae spiders have their sticky vertical threads hanging below. The prey becomes stuck as they make contact with the hanging threads, the glue droplets on the threads enabling this.

These hanging threads have glue droplets so that when prey comes into contact with them, they become stuck. As the prey then struggles, it makes contact with more sticky hanging threads, becoming more entangled. The spider can then come down from the horizontal sheet web above and bite the prey, wrap it in silk and take it up to the web above where it can consume it.

Despite there being many other different structures of web, these are the three which I consider the most unusual. There may well still be more weird and wonderful structures of web yet to be discovered, with evolution constantly driving change in all species of spider and their prey. So, next time you encounter one of our eight legged friends, take a moment to think about the complexity within and between their silk webs.