Species in Britain and Ireland
There are about 650 species of spiders in Britain and Ireland and they occupy a wide range of habitats. Some live in dark corners of garden sheds and buildings, including the common house spiders. Most live out of doors and can be found on plants or running over the soil. Jennifer Owen
found 79 species of spiders in her Leicester garden, from 16 families.
Spiders are predatory animals that subdue their prey by using a pair of fangs to inject it with venom. Most spiders are opportunist predators that feed on a wide range of insects and other invertebrate animals. There are, however, some spiders that specialise in a particular type of prey, such as Dysdera crocata, which feeds on woodlice. All spiders can produce at least four kinds of silk made in internal silk glands, and extruded using abdominal organs known as spinnerets. Even those that do not spin webs will use silk to protect egg masses.
Spiders have a range of strategies for catching their prey. Many produce sticky silk webs, and the spider waits for an insect to fly or walk into the web.
Other spiders do not use webs to catch their prey and rely on active or passive hunting. Wolf spiders, run rapidly over the soil and low-growing plants, relying on speed and their excellent eyesight to capture their prey. Jumping spiders travel in a series of hops and pounce upon their prey.
The crab spiders are ambush predators which sit camouflaged within flowers, and wait motionless for a pollinating insect to arrive. The camouflage can be very effective, making the spider almost invisible until it moves.
Male spiders are often much smaller than the females and can be very different in appearance. A male approaching a female often runs the risk of being mistaken for a meal and they usually make a slow cautious approach to the female. The eggs are deposited in silk bundles that are placed in the spider's web or may be attached to foliage or hidden under loose bark. Some spiders, such as the wolf spiders, carry their egg sacs between their hind legs. The Nursery web spider, Pisaura mirabilis, initially carries its egg sac but then places it in a large funnel-shaped nursery web spun among plants.
The eggs hatch into spiderlings, which are miniature versions of the adult spiders. The spiderlings of some species, such as Araneus
species, remain together in a communal web for a while before dispersing and living separate lives. Lacking wings, spiders cannot disperse as readily as adult insects. Young spiders however can disperse over long distance through a process known as ‘ballooning’. The spider stands with its abdomen pointing upwards and releases strands of silk. When the wind blows, the spider is lifted into the air, with the silk threads acting like a paraglider’s sail. Ballooning spiders
have been observed at five kilometres altitude and on ships in mid-ocean. Recent research1.
has shown that spiders can detect atmospheric electrostatic charges, and that the force this induces on the silk balloon thread is enough to overcome gravity and take the spiderling up into the air.