The Walnut Orb-Weaver Spider

I found this spider crawling around on the side of a shed last summer. With its dark, leathery, flattened body and disconcertingly slow movement, it seemed rather, well, sinister. It certainly appeared much meaner than most of the spiders to be found in the garden: a sneaky, dangerous-looking creature with something of the night about it. Concerned that it might be capable of a nasty bite, I left it well alone.

In fact, this little beastie is a perfectly ordinary, harmless garden spider. Despite being extremely common it is rarely seen as it is mostly active at night. During the day it squeezes its thin body into crevices, often under bark, hidden well out of sight of any predators. Then in the evening it emerges, cautiously, and spins its flat, circular web. Once it has finished this construction it will move to the web’s centre and stay there perfectly still, waiting for unwary flying insects to get trapped.

If the spider feels spooked during the night it will return to hide in its crevice, slowly following a guideline of silk. Before the sun rises it completely dismantles its web, leaving no trace that it was ever there. Given that the webs can reach 70 cm in diameter, this daily cycle of building and demolition seems like an extraordinary waste of effort. Maybe all this work just fills the time, or maybe the webs are actually a bit naff and so wouldn't last more than a night anyway.

If you spot one of these spiders it's likely to be a female. These are bigger, at up to 15 mm long, and are active all year. Males on the other hand only ever grow to 9 mm and are only out and about during the summer. Interestingly, if you pick up a male it may bite you, although however hard it chomps down it won't do you any real harm. The Walnut Orb-Weaver would seem therefore not to be the villain it appears. It does 'live in the shadows' as its Latin name Nuctenea umbractica implies, but this is simply because it is too cowardly to come out during the day.

Hermit crabs

Hermit crabs are a common sight by the seaside, most often spied crawling around in rock pools. Adults vary in size from around 15 to 150 millimetres. Their most prominent features are their shells, and yet these are not really part of the crab at all. Most crabs have a hard carapace that they produce themselves, but hermit crabs have soft, easily-damaged bodies and would quickly be killed without further protection. Because of this they search out the empty shells of gastropods such as whelks and periwinkles. As they grow they have to find bigger shells that can accommodate their increased body size. There is often much competition for the best shells, but once a crab has successfully obtained one it will insert its asymmetrically twisted abdomen far inside until only the front two pairs of legs remain out in the open.

Technically the crabs have five pairs of legs, but the back two of these are too small and puny to be much use for anything other than holding on to the shell, and so remain tucked away inside. The second and third sets are larger and stronger and so are used for walking, but even these are dwarfed by the first set. The front right leg has a large claw that is used for holding food and for fighting, and the smaller claw on the front left leg is used to help with eating.

Hermit crabs aren't fussy about what they eat; if they can catch it they'll have it. Any animal and vegetable matter scavenged from the seafloor will do. The crabs often have a symbiotic relationship with other creatures such as sea anemones which come and live on their shells. The crabs get camouflage and protection and in return the anemones get to eat any leftover food. Sometimes this relationship becomes so established that the anemone will 'move house' along with the crab when it changes shells.

Male hermit crabs can be quite aggressive when the time comes to mate, and will grab hold of female crabs, fighting off any competing suitors with their large right claws. Male reproductive organs are located behind their rearmost legs whereas those of the female are on the third pair. On the left-hand side of the female abdomen are structures known as pleopods which are used to carry the fertilised eggs. The baby hermit crabs do a fair amount of their development whilst tucked away here inside the eggs. When they eventually hatch and venture out into the sea they are tiny, shrimp-like creatures in desperate need of a shell.

This hermit crab lives in a tank at the Anglesey Sea Zoo, a small aquarium that only has native sea creatures on display. It is well worth a visit, with its lobster breeding programme being a particular highlight. The zoo is also a good reminder of what a great range of sea life we have in the UK, and reinforces the fact that creatures don't have to be exotic to be interesting. Great satisfaction can be derived from learning about the animals 'indoors' and then going and finding the wild versions just outside.

Anglesey Sea Zoo

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