Looking for a date

The other evening I spotted a rather handsome spider making its way across the tiled wall behind the kitchen sink. It was one of the Tegenaria spiders, a group of several rather similar looking species and the bête noir of arachnophobes everywhere. These are the large ‘house’ spiders that you often encounter in the autumn as they run across the living room floor or become ‘trapped’ in a bath or sink.

Several of the species can only be reliably identified through careful scrutiny under a microscope and identification is additionally complicated by a degree of hybridisation between species, something that is rampant in some parts of the UK. This individual was a male, rather small in size and with the legs spanning just a couple of inches. Under a hand lens I could see the delicate legs, the subtle markings that chequer-boarded its abdomen and the modified palps, which form the male’s sexual organs.

This male was presumably wandering around looking for a female, the larger of the two sexes. Once he found a mate he would live with her for several weeks before eventually succumbing to old age. After death his body would feed the female and provide additional nourishment ahead of her producing a clutch of eggs. Female Tegenaria spiders are often overlooked because they spend most of their time within their webs. The silk used in these is not sticky; each web is long-lasting and may be used by a succession of spiders over time as the original occupants die and are replaced. Individual females may live for several years.

Although several Tegenaria species show a strong association with domestic and business properties they can also be found in other habitats, living amongst rocks, stones or fallen timber. The association with buildings is an interesting one. The conditions found in our homes do not necessarily lend themselves to spiders or other invertebrates, being dry and lacking in potential prey. Fortunately, house spiders can cope with the dry conditions and they can also go for long periods without sustenance. It is worth noting that they rarely bite and, apart from the webs that they make, you could say they make welcome and unobtrusive house guests.

Some autumn insects

I found the remains of an old lady the other morning. Actually, to be more specific and somewhat less macabre, I found the wings from an old lady moth. The wings were on the floor of a passageway that runs under part of the house and out onto the street. This sheltered spot is well used by brown long-eared bats, which often bring the larger moths into the passage so they can devour them while clinging to the wall. The boldly marked wings of this large moth are easily recognised and they stood out from the remains of other species, taken more commonly by our local bats. The weather has been such recently that I have seen few moths against the kitchen windows of an evening and this makes me wonder if the bats are beginning to find things a little difficult. They have not had a good year by all accounts, with reports of underweight individuals and others seen on the wing during daylight, stressed by the lack of insect prey. It could be difficult for them going into the winter that lies ahead.

I have not experienced a late summer flush of other insects either, with few migrant moths and hoverflies evident in the garden. Not that there has been much late-summer nectar for them – the sedum and nettle-leaved bellflower only coming into bloom over the last few days. At least the sedum has been available for the small influx of red admiral butterflies that has been on the wing during those days when the sun shows against a bright blue sky. Late September and early October can be a reasonable time for insect immigrants; Camberwell beauty, a very impressive butterfly, tends to occur at this time of the year, although in very small numbers. The Camberwell beauty immigrants originate from Denmark, Poland and Sweden, which is why Norfolk delivers the greatest number of records in most years. It has been a while since the last major influx of this species and it is now very unlikely that we will see any influx this year.

There are invertebrates around if you know where to look though and can get out and about ahead of the first frosts. Bush-crickets can still be found in our hedgerows, along with various flies and smaller wasps, and there are plenty of spiders around at the moment, including some of the Tegenaria species that may be encountered dashing across the living-room carpet during the evening. There is a sense, however, that things are winding down, retreating ahead of the approaching winter and readying themselves for a sustained period of inactivity. Every now and then though you might still stumble across something of interest.

Arachnaphobes look away now

I spent part of the weekend taking down an old shed that had reached the stage where new repairs would be pointless, the main structure rotten and unstable. As well as the pale shoots of ivy that had penetrated the crumbling boards, the shed held evidence of other lodgers. Two neatly made nests, each a mixture of moss, leaves and shredded plastic hinted at the presence of Wood Mice, something confirmed by the numerous Hazel nuts, carefully opened at one end by sharp teeth. There were woodlice in the damp corners and a huddle of snails in an old terracotta pot. It was the spider webs and their silent occupants that were of greatest interest, however, and these covered much of the wall space, particularly so in the corners and where uprights held the horizontal lapboard in place.

A few of the spiders were sizeable beasts; these were large Tegenaria house spiders of the sort encountered in the house during August or September, when the newly mature males wander in search of receptive females. The size of these arachnids makes them the bête noir of those suffering from arachnophobia but I find them rather engaging.

I could not be sure which of the eight Tegenaria species I was looking at, even though there were clear variations in size. Several can only be reliably identified through careful scrutiny under the microscope and hybridisation between species is rampant in some areas. The larger individuals seemed to occupy the largest webs, perhaps reflecting some variation in age since house spider webs are long-lasting. The silk used in these webs is not sticky, which may explain their longevity, and a web may be used by a succession of spiders over time as the original occupants die and are replaced.

The chances are that most of these spiders were females, since the mature males typically die early in the winter, having mated and leaving the mature females and immatures to sit out the cold weather. Come the warmer conditions of spring, the mature females should see an increase in prey availability and the resources needed to develop the eggs that will be deposited in a series of egg sacs. Each egg sac, made of white silk, is about the size of a small marble and may be decorated with prey remains; it will be deposited close to the web. I could not see any egg sacs, so I hoped that these spiders, about to be evicted from their current home, would find somewhere else to set up.

House spiders also occur away from human habitation, living under debris, within tree cavities or within rock crevices, but no doubt the replacement shed would soon be occupied.

The deadly hermit

Living in an old house means that I live alongside spiders; from the delicate daddy-long-legged forms that hang in the upper corners of rooms to the scuttling species of Tegenaria that race across the floor at the end of summer. I also encounter spiders when I am out and about looking for beetles and it may be this that has increased my interest in these much-maligned creatures.

Although we lack any truly threatening species, there are a number of spiders found here that are seriously impressive, their bulky forms and large fangs sufficient to menace the casual observer. One of these is Atypus affinis – sometimes called the purse web spider – a primitive species that is closely related to the trap-door and bird-eating spiders that one often sees in television documentaries. Atypus is a scarce spider (there is just one Norfolk record) but it is widely distributed across the southern half of Britain. One reason for its scarcity may be its requirement for undisturbed grassland and heathland habitats; another may simply be that it is easily overlooked due to its largely subterranean habits.

Atypus lives a hermitic existence, cocooned for much of her life in a sealed silken tube within a burrow excavated in the soil. The silken tube can be up to 39 cm in length but is more usually 20 cm or so long, with about a third of the tube showing above ground. This ‘above ground’ portion of the tube is camouflaged with grains of sand and other debris and can easily be mistaken for a piece of old root. The spider waits within her silken tube until some insect wanders across its surface; then she strikes, her huge fangs puncturing the silk and stabbing into the victim. The fangs hold the victim in place, pinning it to the web and, once subdued, the spider disengages one of her fangs, using tiny teeth on the base of her chelicera (the basal part of the jaw to which the fang is attached) to saw through the silk, opening up a slit through which the victim can be drawn into the cocoon. Once inside, the spider takes her meal to the base of her burrow before returning to repair the slit, ready for the next unfortunate insect to wander by.

During the winter months the spider will effectively hibernate at the base of the burrow, the upper section of the web shrinking back to become even more root-like. Come spring and the top section has to be rebuilt, a process that may be carried out annually for the seven or so years of life that a fortunate Atypus may enjoy. As the great scholar of spiders, W. S. Bristow, noted ‘this is a spider of distinction’.