Tag Archives: arachnology

If Spiders were Teddy-bears

I know this blog is slightly in danger of becoming overrun by False Widows and other spiders, but there is one interesting species I haven’t mentioned enough, which you can see walking about on your house in broad daylight – the Zebra Spider, the most common species of jumping spider in Ireland. And it does look like a cuddly little teddy-bear.

A female Zebra Spider. She's tiny, and no matter where you live in Ireland there is almost certainly one walking about on the outer wall of your house hunting for tiny insect prey. They look nothing like other spiders, and don't make webs, hunting on foot on sunny walls.
A female Zebra Spider. She’s tiny, and no matter where you live in Ireland there is almost certainly one walking about on the outer wall of your house hunting for tiny insect prey. They look nothing like other spiders, and don’t make webs, hunting on foot on sunny walls.

The Zebra Spider gets its name because many of them have black stripes on their white firry backs, particularly the males. However, the males also have massive black fangs which they use in the same way that stags use their antlers – to fight for females. Zebra Spiders are usually around 5 or 6mm long, rarely reaching 8, and they have very short legs. They leap on their prey and if you approach one it will lift its head and look you straight in the face with those huge binocular-like eyes mounted at the front of the head. They also possess a bizarre ability to leap across the faces of walls, and they can walk across glass windows with ease. Stare at any sunny wall on any building for a few minutes and you will spot one.

Spiders and Cases of Mistaken Identity

The Missing-sector Orb-weaver, Zygiella x-notata, above, can sometimes be mistaken for the False Widow Steatoda nobilis, but is usually much brighter in colour, smaller in size and makes a completely different web.

Many spiders are very similar, and there is a lot of worry of some of them due to the colonisation of Ireland by False Widows in such numbers these days. The spider that is mostly mistaken for a False Widow is the very common Missing-sector Orb-weaver, Zygiella x-notata, which is found around the windows of houses in huge numbers. Zygiella doesn’t get to be as big as False Widows can, but since many False Widows encountered are not fully grown, then confusion is inevitable. What Zygiella does is spin a classic spider-web across the front of windows so that insects flying to the windows at night will crash into them and become entangled.. Most orb-weaving spiders spin their webs across fly-ways in the same way that poachers cast nets across rivers. But remember, the False Widows don’t do this because they target different prey. So the dozens of spiders camped around the outside of your window-frames will almost certainly be Zygiella and not False Widow. But they have a very similar body-shape and markings on the back can be superficially similar. Zygiella is usually much brighter and tends to have a silvery appearance.

On the other hand, the male Steatoda grossa False Widow, which has been recorded in Ireland since the late 19th century, can be mistaken for a House Spider, as it has very long legs and tends to scuttle along the ground and will enter houses simply by walking into them, and in this manner is extremely different to the more robust-looking Steatoda nobilis male. Unlike the females, they are not known to bite, but these spiders can get quite large (about as big as a mediu-sized House Spider)  and will frighten most people. The markings on the abdomen have a checker-board appearance like the classic markings of the female.

A large male Steatoda grossa (the smaller of the two large False Widow species found in Ireland). This spider prefers to scuttle rather than climb and can easily be mistaken for a House Spider when first seen.

A few more notes on Autumn Spiders

Some people are worried that the spiders that start appearing in autumn are banded together into small gangs hell bent on mischief. That couldn’t be further from the truth, and the reason the numbers get smaller is largely due to the effects of these big spiders on each other. They are often extremely territorial, and in the photo below you can see a female being driven from her web in an old shed by another female of roughly the same size.

The Tegenaria on the left is still sitting in the extremities of her web, but the intruding spider on the right is much closer to the entrance, preventing her from returning.

The spider left her home and fled while the newcomer decided to set up camp, and made the fatal error of straying to close to a neighbouring False Widow (Steatoda nobilis) which made short work of her. Almost all spider species will prey on each other, and sometimes members of the same species (cannibalism) but it is important to realise that the difference between one spider species and another can be as vast as that between a human being and a cow or any other mammal, and maybe even more so.

A large and dark female False Widow, Steatoda nobilis, with a large House Spider as prey. Spiders are an important part of many spiders prey.

Despite the massive appearance of large Tegenaria duellica House Spiders (the legs would easily span the palm of my hand) the bodies are never quite so large as they appear to be. The largest House Spider I ever saw appeared to have an abdomen of three centimetres in length (an inch) but when I measured it accurately with a scientific ruler I was very surprised to discover its body measured exactly 23 centimetres. And, of course none of these species are the largest in Ireland. That honour falls to a much more impressive creature, the Raft Spider, Dolomedes, which lives in swamps and bogs and hunts frogs and small fish among many other things. When I get a good photo ( I have a bad one) I’ll post something about that very handsome monster.