Tuesday, 6 October 2015

Philodromidae: running crab spiders

This family has over 500 species worldwide, but just 15 in the UK. The most abundant genus is Philodromus, relatively small spiders, which do not build webs and bear a superficial resemblance to crab spiders (Thomisidae), although they are not closely related to them. Some species are very similar and require microscopic examination of female genitalia and male palps for identification. The genus Tibellus, includes a couple of British species that live on grass and have an elongated body and legs that stretch forward and back.

Ambush or pursuit hunters
Philodromus have long, but robust legs, specially the first two pairs, and like to bask with legs curled up like wolf spiders or nursery spiders. They can be ambush predators, often sitting atop flowers or foliage in trees or bushes, legs outstretched, awaiting prey, although they can also run fast pursuing prey or escaping predators.

The strategy of waiting on flowers pays off for this Philodromus, who got a juicy fly.
Although Philodromus does not build a web, it uses silk as a safety line - which you can see in this photo of one in ambush on a flower.

Colour change
These spiders can be strikingly well camouflaged on their habitat, which can include lichens on tree trunks, heather or sandy beaches. Some species even have the ability of changing the depth of colour to match their surroundings. A species that lives in lichensPhilodromus margaritatus, is hard to spot when sitting on them, and it can also change colour from green to white or grey depending on her surroundings.

Iridescent males
The males of some Philodromus species can look quite different in color pattern to the females. In some species males are iridescent.
The beautiful iridescent male of Philodromus aureolus. The female looks like the individuals in the photographs above.
This is another male Philodromus with iridescence, and just six legs.

Spiders are not particularly known for their ability to regenerate body parts. But it is not unusual to see Philodromus with legs missing. The specimen with the fewest legs I've seen is four, only one left on one side, and yet it seemed to move about freely over flowers. It looked like it used its remaining palp for balance.
If leg loss happens in young individuals they can be regenerated as they grow a new leg, thinner and shorter than the original, in the next moult. 
This Philodromus sp with its aphid prey has regenerated the two middle legs on the foreground, which is thinner and shorter than the other and has a plainer appearance.
Philodromus basking on a sunny spring day.

 And to finish this family's post, a photo of an individual of the genus Tibellus, with a very different appearance to Philodromus.

Pholcidae: cellar spiders

The Pholcidae is a large family of spiders, although most of the family's diversity is in dry temperate or subtropical regions, where they can live in diverse habitats away from houses. In our latitudes, these warm loving spiders live in caves, cellars, wells, outbuildings, and houses. The most common and widespread species in the UK is Pholcus phalangioides - a male with his rounded palps is on the top photo-, which has also now been introduced in other regions of the world, including North America, from its native Eurasian range. There are several common names for this spider, one of them, daddy long legs, is certainly confusing, as it is also applied to crane flies and harvestmen. They like to build their almost invisible tangled webs on ceiling corners, from which they hang upside down looking like thin chandeliers. Their legs are, indeed amazingly long and thin relatively to the body.
The natural history of Pholcus phalangioides is easy to study, as they don't move much, residing for weeks on end motionless on quiet corners of the house, and are present year round. 
A pair mating. Mating can last more than an hour. Males are slightly larger (10 mm) than females (9 mm).
Mummy long legs
As many other spiders, Pholcus take extended care of their offspring. They hold their eggs with their chelicerae until they hatch. The egg brood is kept together by a few silk threads.
A gravid Pholcus, she laid eggs the following night. She resided under the outside toilet shelf.
Here is the same individual with her newly laid eggs.
These eggs are going to hatch soon. The linear whitish patterns in the eggs are the legs of the developing young.
In about two to three weeks, spiderlings hatch. Right after emergence, the spiderlings remain together for a few hours, before moving onto the mothers surroundings.
The Pholcus under the shelf, with her record number of offspring, I counted 65 (30 is the average).
Pholcus mother with her meal, another spider, surrounded by her offspring. She will set her egg sac aside to feed or to mate, and may lay further egg batches after the young spiderlings have dispersed. These spiderlings are almost ready to disperse, having had their first moult.

Spider hunters
Despite their fragile, spindly appearance, Pholcus are fierce predators, and regularly hunt other spiders, often much larger than themselves, including house spiders (Tegenaria) and woodlouse hunters (Dysdera). They achieve this by quickly wrapping the other spider on silk using their long legs, which allows them to keep their distance. Once thus subdued, they bite their prey. Pholcus uses a sit and wait approach, which is probably very successful during the autumn, when male house spiders move about in search for females. They can also use an ambush approach, moving about and, when it finds another spider's web, it will make it vibrate to attract the owner.
They don't always succeed in spider hunting, through, and I have seen other spider, the mouse spider (Scotophaeus blackwalli) with the remains of a Pholcus
Another successful Pholcus with prey spider.
Pholcus with woodlouse.
A Scotophaeus blackwallii with captured Pholcus.

Monday, 5 October 2015

Uloboridae: Cribellate orb-weavers

 Although not a particularly small family, only three species of Uloboridae are found in the UK, one of them, Uloborus plumipes only a recent colonist. They are very unusual spiders in many respects. The Uloboridae are cribellate spiders, they produce many fine threads which they comb using a structure on their rear legs formed by a row of short bristles, resulting in characteristic wool-like or frizzy threads.
 Uloborus plumipes the 'garden centre spider' (above) is typically found only inside garden centre heated glasshouse, and rests with her oversized and spiny forelegs together ahead of her, looking like a piece of debris on her orb web.

No venom
Another unusual feature is that, unlike most other spiders, they have no venom glands: they rely on quickly wrapping prey on silk and only bite once the prey is so immobilised.

Orb weavers
The orbs produced by Uloborus plumipes have a striking resemblance to Araneid webs, although other members of the family have more unusual asymmetric webs. Despite this, they appear to have evolved orb-weaving independently of the Araneae.
The orb web of Uloborus plumipes
The resting Uloborus with its characteristic posture on its orb-web.
The unusual spiky egg sac of Uloborus plumipes, which looks like a shrivelled piece of leaf or seed. You can see the woolly texture of the silk threads securing it.

Sunday, 4 October 2015

Scytodidae: Spitting spiders

Spitting spiders are a small family, with just one British species, Scytodes thoracica. They are small (3-6 mm, female larger than the male) but easily recognisable with a dark markings like line drawings over paler background and clearly annulated legs. In the UK the spitting spider lives inside buildings, mainly in the south. It is a nocturnal wandering hunter, which does not build a web, and can be encountered prowling on walls. It has six eyes, with a characteristic arrangement. Males and females are very similar, and both the female genital opening and male palps are simple.

A glue shooting spider
The common name of Scytodidae comes from their unique method of capturing prey. They have a relatively large domed cephalothorax, larger than its abdomen, which holds paired glands which produce both poison and a glue-like substance containing silk. The glands open in the fangs and the spider is able to aim at potential prey at distance and shoot a mixture of glue and venom while swaying the fangs. The resulting paired zigzag pattern of gluey-silk strands entangles the prey and attaches it to the ground. The spider also uses its squirting action against other spiders larger than themselves.

Spitting spiders make a simple egg sac. The eggs are large, and each batch contains 20-35. The female holds the egg sac with her palps and spinnerets, and can feed while carrying the eggs. The spiderlings emerge from the egg sac, and hang from a web the mother builds from them. After about 10 days, the moult and disperse. They are slow developers, and long lived for such small spider, females mature at two to three years old and can live up to five years.

Scytodes thoracica on a wall
Feigning death when disturbed.
Face on view.

Saturday, 3 October 2015

Linyphiidae: sheet weavers and money spiders

Linyphidae is the largest spider family in the UK, with 270 species. Most of these are tiny, dark and and only identifiable with a microscope, the 'money spiders'. They typically build hammock-like webs held by a pattern of criss-crossing threads above and below. Liniphids usually hang upside down from their sheet web and do not use a retreat.
One of the largest species is the common Linyphia triangularis (above) whose webs hang in numbers from bushes in gardens and become very evident when covered in dew.
Neriene montana, is another large species (4-7 mm) common in gardens.

Stemonyphantes lineatus.

Gosammer and ballooning
These spiders can be incredibly numerous and active, and their drag silk threads can give fields a silvery shine, which is called gosammer. Money spiders disperse by ballooning. They climb up bushes and release a long silk line, which can get caught in the wind. Standing on tiptoes, the spiders are pulled up and lifted into the air.

A close-up of a gossamer-covered grass seed-head with money spiders ready to balloon.

Mating tactics
Linyphia has some interesting mating tactics I have blogged about before. Males have large chelicerae they use to fight other males while they guard a female.
Linyphia triangularis pair, the male is on the foreground. Males often sit on the female's web, mate guarding.

Money spider heads
Some money spiders have very unusual heads, with some of their eyes on top of turrets or humps (see if you can make sense of Walckenaeria!). These harbour glands that produce secretions, possibly nuptial gifts, during mating. Females of some species are known to hold the male's head during mating.

Egg sacs
Egg sacs are set near the web, and the females can sit on top of it guarding it.
Neriene montana near her translucent egg sac.