Thursday, 29 October 2015

Liocranidae: spiny-legged sac spiders

Credit Gerhard Elsner CC BY 3.0 via Wikimedia Commons.

A small family with 13 British species that used to be regarded as part of Clubionidae. All species are mainly nocturnal wandering hunters, except the two species of the genus Phrurolithus, which are diurnal ant mimics, and have been also regarded as a different family.

Distinctive egg sacs
Agroeca have distinctive stalked egg sacs, like inverted wine glasses (top shot), sometimes covered with soil, which are seen more often than the spider, as they are not guarded. Other species guard their egg sacs.

Parasitoids
Spiders have many species of external and internal parasitoids, most of them ichneumonid wasps. Some external parasitoids attach themselves to adult spiders and feed on them, other species search for cocoons and inject their eggs on egg sacs, with the parasitoid larvae developing on the eggs. The characteristic egg sacs of Agroeca makes them easy to identify and collect, so in a study of spider adult and egg sac parasitism in Germany, up to 66% of Agroeca egg sacs were parasitised. Four species of parasitic wasps emerged from egg sacs: two small Gelis wasp species, Bathythrix formosa, and Thaumatogelis audax. Few or no spiderlings emerged from the parasitised egg sacs, indicating how important parasitoids can be as a source of spider mortality.

More information
Finch, O. D. (2005). The parasitoid complex and parasitoid‐induced mortality of spiders (Araneae) in a Central European woodland. Journal of Natural History, 39: 2339-2354.

Wednesday, 28 October 2015

Anyphaenidae: buzzing spiders

Credit gbohne, CC BY-SA 2.0, via Flickr.

A mainly American family with a single UK species, Anyphaena accentuata, that can be recognised by arrow head markings on the abdomen. They are good climbers that live on the foliage of trees in woodland and scrub, where they hunt and mate. They are active hunters that pounce on insects that sit on leaves such as leafhoppers, aphids and flies.

Buzzing spider
Males of this species (top shot) use acoustic cues in courtship, vibrating the abdomen and tapping with the palps while sitting on a leaf. This produces an audible noise (which may be undetectable for older people), so Bristowe suggested the name buzzing spider for them. This is a short clip of this behaviour. Females may respond to these signals by approaching the calling male. Females attach their egg sac to the underside of leaves and guards it in a thin silk cell.

Cold adapted
Immature buzzing spiders are active year round and have physiological adaptations to activity during cold temperatures, even below the freezing point. In the winter they prey on small insects that live on bark.

Tuesday, 27 October 2015

Dictynidae: mesh weavers

Credit: Drriss & Marrionn CC BY-NC-SA 2.0 via Flickr.
These are small cribellate spiders, less than 5 mm long, some with characteristic colour patterns. They build an irregular sheet web usually with a central retreat. Many of the 18 British species are uncommon. Some of the species live on plant foliage, others are ground dwellers.
 The top shot shows Nigma walckenaeri a green and white spider that builds sheet webs on the top surface of leaves. This species is mainly found in the Thames and Severn valleys, where it can be common in gardens.

'Unusual friendship' between males and females
 Dyctina arundinacea, the most common species, makes its web atop a dead shoot or flower head. The spider adds more threads as the summer progresses, for, unlike orb weavers, the web is a permanent structure. Bristowe remarked that in this species, the male spends an unusually long time in company of the female in her web (a month or more). Once a male enters a receptive female's web, he signals to her and she signals back with vibrations and tactile signals. The male then goes on to modify the female's web and adding threads to build a canopy, where mating happens. They signal to each other every time they meet. Males and females can even share capture and eating of prey. The female sets her egg sacs inside the web, and she can produce up to six in a season. While a male have to gain from staying around a female, for example, preventing rival males from mating with 'his' female, it is unclear what the female has to gain from accepting the male, unless his cooperation in prey capture helps she build up resources for egg production. More research is needed on these spiders natural history. There are tantalising observations of  males possibly participate in egg guarding. Some non European Dictynidae are social, so it is possible that the roots of social behaviour lay on these unusual male-female associations.

Monday, 26 October 2015

Zodariidae: ant spiders

Credit: Christophe Quintin, CC BY-NC 2.0 via Flickr.
This relatively large family is distributed mainly in tropical and warm temperate regions. There are four species in the UK, all from the genus Zodarion, and all of them appear to be recent arrivals with first records from 1979 onwards, although there have been suggestions that at least one of them is native. They are very local and tend to be found in the south of England where they live in dry, warm and open habitats in association with ants.

Ant-looking ant-eaters
Spiders of the genus Zodarion are ant mimics: they resemble ants in size, shape and also behaviour. The resemblance goes as far as the microscopic pattern of spines, bristles on legs, cephalothorax and abdomen as ants. Even the effect of a shiny ant body is achieved with ridges in their cuticle. They also imitate ant gait and tactile signals: they deceive ants by tapping with their first legs, as ants do with their antennae. Mimicry is thought to offer them protection from spider predators that avoid ants. But they are also aggressive mimics: they use the resemblance to ants to approach unnoticed, as they feed exclusively on ants, using ambushing tactics. Once they capture an ant, they hold its body ahead of them and present it to approaching ants, a behaviour known as 'shielding', at the same time tapping the antennae of the ant. This way they imitate the behaviour of ants carrying dead corpses away from the nest.

Igloo makers
When resting the spiders take shelter in curious igloo-shaped refuges made with small pieces of debris and tiny stones (see photo below). They also lay their eggs in their retreats.
Credit: Korenko S, Schmidt S, Schwarz M, Gibson G, Pekar S , CC BY 3.0, via Wikimedia Commons.

Sunday, 25 October 2015

Cybaeidae: water spiders


Credit: Norbert Schuller CC BY-SA 3.0 via Wikimedia Commons

The only British species in this family, the Water Spider Argyroneta aquatica, is the only known spider that lives almost permanently under the water surface. It inhabits clear ponds, ditches or slow moving streams. Despite their ability to dive and swim freely, their adaptations for aquatic life are subtle: the fine hairs of their abdomen and front of cephalothorax trap a silvery lining of air when the spider is under water, and the two pairs of rear legs are covered with rows of long fine hairs, which help with swimming and collecting air bubbles. They are grey and brownish spiders that can reach large sizes (sometimes over 2 cm).

Inside diving bells
The water spider builds an underwater refuge made of a dome of silk attached to submerged plants which she fills with air. This takes several trips to the surface, trapping large air bubbles with the aid of her rear legs, and then releasing the air out when she is under the dome. The dome then acquires a bell shape and effectively acts as an external gill. The spider spends much of its time in the bell, as oxygen diffuses from the water into the air bubble as the spider uses it up. Moulting either takes place inside the bell or on the water surface.

Reverse size dimorphism
Unlike most spiders, water spider males are on average larger than females. This could be due to the different hunting strategies of males and females: males are more active hunters and spend more time diving outside their bells, and large males are better divers than small ones in moving inside water as they are better counteracting air buoyancy. Females build larger bells and, in contrast to males, tend to practice ambush hunting from their bells, sitting head down with her front legs by the entrance, where they can detect vibrations of passing prey. Both males and females take their prey to their bells to eat.

Reproduction
Mature males (top shot) leave their bells in search for females. Mating takes place in the female's bell, although it involves both male and female swimming outside the bell. When mating, females prefer larger males, but they are also more wary of them, as - also uniquely to them - male water spiders are known to occasionally cannibalise females (although the reverse also happens). Females sometimes lose their bells after rejecting a male.
The female lays her eggs in her bell, in a thick white egg sac at the top of the bell. She partitions this area out with silk and remains in the bottom part of the bell herself. She stays there on guard until the spiderlings hatch. After a few moults they disperse and they quickly build their own little bells under water. Females can lay several egg clutches in a season.

Empty snail shells
At the end of autumn, the spider reinforces the bell with more silk, closes it and stays in it through the winter months. An alternative winter home are empty pond or ramshorn snails, lined with silk and filled with an air bubble.

More information
Schütz, D., & Taborsky, M. (2003). Adaptations to an aquatic life may be responsible for the reversed sexual size dimorphism in the water spider, Argyroneta aquatica. Evolutionary ecology research, 5, 105-117.

Schütz, D., & Taborsky, M. (2005). Mate choice and sexual conflict in the size dimorphic water spider Argyroneta aquatica (Araneae, Argyronetidae). Journal of Arachnology, 33, 767-775.

Saturday, 24 October 2015

Oxyopidae: lynx spiders

Credit: Ferran Turmo Gort, CC BY-NC-SA 2.0 via Flickr

A mainly tropical family, with just one British species, Oxyopes heterophthalmus, a small, cryptically coloured spider. Their long legs are furnished with stout long spines which may help in prey capture. They are diurnal, very agile visual hunters that run and sit amongst flowers and other low vegetation, often ambushing pollinating insects (top shot), but they can also pounce on prey. No hunting webs are made.

Local heathland specialist
Oxyopes heterophthalmus lives in sheltered mature dry heathland. It is found in some small sites in Surrey, and is probably declining although it can common in some sites. Although it used to be found in the New Forest, it hasn't been seen there for over a century.

Life cycle
Adults are found in May and June. Courtship involves visual palp signals and vibrations by the male.
Females sit guarding their large, flattened egg sac in July at the top of plants. They might need two years to become mature.

Friday, 23 October 2015

Eresidae: velvet spiders

Credit: Viridiflavus, licensed under CC BY-SA 3.0 via Wikimedia Commons.


The Eresidae is a small family of about 100 species, mainly distributed in the Old World. They are interesting as several species have independently evolved social behaviour: closely related individuals live in groups through their lives, cooperating in building communal nests and capture webs, prey capture and brood care. Thus, they are able to subdue larger prey, which they also share. There is just one British species, the Ladybird Spider, Eresus sandaliatus, which has managed to survive against the odds. They live in sandy, sunny slopes in lowland heather, building their tubes in the ground. Its common name only applies to the adult male (top shot), which, in contrast to the uniform velvety black of the females, it is a striking spider, with black legs ringed with white and a bright scarlet abdomen with six paired black spots. Females rarely if ever leave their burrows, while males wander in the spring in search of females. They are cribellate spiders, that is, they produce woolly silk that they brush with comb-like bristles on their rear legs and trip threads cover and surround each burrow.

Suicidal maternal care
Ladybird Spiders have a slow development and a high degree of maternal care. Males take three years to reach maturity, females take four. Males mature in the autumn, but overwinter as adults. In the spring, males emerge from their burrow and wander in search for mature females. After mating, the female produces her only clutch of eggs and guards them in her burrow. When the spiderlings hatch, she feeds them by regurgitating a nutritious liquid created as her internal organs liquefy. After a few days, she stops feeding the young and lets the spiderlings climb onto her body and feed from her, her disolved organs prepared to maximise the nutritional value to their young. Before dispersing, the spiderlings share the maternal burrow, adding to the silk threads.

Conservation
Ladybird spiders are highly endangered in the UK and listed on Schedule 5 of the Wildlife and Countryside Act. Between 1816 and 1906 a total of six males and one female had been collected in the Bournemouth and Poole area, but none after that. The species was feared to be extinct, as the lowland heathland where they had been found had been lost to land development. In 1958 W.S. Bristowe stated in his book The World of Spiders:
I do not despair of Eresus being found in Britain again, and [...] I hope clues may help some lucky person to experience the thrill of feasting his eyes on the brilliant beauty of the wandering male...If anybody finds Eresus before I do, I shall feel no resentment.
Bristowe narrates a tantalising account of a shopkeeper describing a spider just like a male Eresus, his family had observed in Cornwall in 1932. He did visit the exact site, but he was not to be the lucky re-discoverer. He goes on giving many tips on the best way to look for the species, informing the reader on its natural history, which he was familiar with from his experience with the species in mainland Europe.
 Curiously, Bristowe died in the early days of 1979, the same year that the species was rediscovered in the UK in a small remnant of heath in Dorset, and he was probably never aware of the rediscovery. By 1992 the population was estimated to comprise fewer than 40 individuals and a captive breeding plan was established, first trialling the methods with the less endangered Danish spiders od the same species. As concurrent habitat management of the existing population was very successful and the population of the original site increased substantially, native spiders have been reintroduced to suitable heathland areas within the historical distribution range. The reintroduction program, which is ongoing, has been a success and there are now eight established populations in various patches of suitable habitat (you can donate here).

Thursday, 22 October 2015

Sparassidae: huntsman spiders

Photo credit: Ettore Balocchi, CC BY 2.0, via Flickr
A family of over 1000 species, mainly found in warm regions. There is just one British species, Micrommata virescens, the Green Huntsman, a large, and vividly green spider unlikely to be confused with any other. While females are all green (above), males are also marked with red stripes alongside the abdomen. Its eight eyes are arranged in an oval pattern and are surrounded by white hairs like eyelashes. This spider lives in damp woodland clearings and rides, where it can be found on the lower branches of trees, oak saplings and grass tussocks. It's mainly diurnal and it does not build a web, instead relying on its camouflage: sitting head down waiting for prey to come near.
The Green Huntsman is an uncommon and local spider, mainly found in the south of England (click here for a distribution map) and it also appears to be in decline. As it grows relatively slowly, taking 18 months to reach maturity, populations may be adversely affected by cold and wet springs.

No courtship, long copulation
Males mature in May and June and have a very short season. They grab females if they find them, with no preliminaries, but copulation is long.

Leaf huts
When ready to lay, the female locks herself  in a large leaf retreat made by attaching together and lining several leaves with silk. She wraps her green eggs on a whitish egg sac, and remains in this retreat until the spiderlings disperse. A second brood may be produced.

Wednesday, 21 October 2015

Atypidae: purse web spiders

This is the only family of mygalomorph spiders in Northern Europe, relatives of the tropical American tarantulas. Although the Western Mediterranean region holds over 40 species of Mygalomorphs, including trap door spiders and funnel-web weavers, there is a single species in the UK, Atypus affinis, the purse-web spider. These spiders have massive forward facing chelicers which open and move vertically and are furnished with saw-like teeth underneath. They are multipurpose tools, and are used for digging, moving soil about, cutting its silky tube and crushing prey.

Silken socks
Purse-web spiders spend most of their lives underground, at the end of a sock-like silk tube sealed at both ends. A part of the tube is underground (up to 50 cm deep), and the rest, likened to the finger of a glove, runs across the surface, partly camouflaged with debris and soil. When the spider feels the vibrations of an insect walking on the exposed tube, she darts up, punctures the tube with its opened fangs, stabbing the insect and dragging it into the tube through a slit cut with her fangs. She will then repair the tube and may eventually throw the remains of the prey out.

Wandering males
When males mature in September-October, they leave their purse-web and wander in search of mature females. This is the only stage of their lives, apart from the initial dispersal of spiderlings from their mother's burrow, that they leave the comfort of the underground. If a male finds a female's tube he freezes and taps it a few times with his palps, pauses and taps again. If the female does not respond with aggressive tugging, the male makes a slit in the tube and enters. After mating the male lives with the female for the winter. He might die and be eaten by the female or it might escape in the spring, when males may again be seen wandering in the open.

Slow development
The female makes her egg sac at the bottom of the tube in the summer and the spiderlings hatch in the following spring, some eighteen months after she mated. The young (about 100 per brood) remain with their mother until they are almost one year old, and then, a sunny day of spring, they will emerge from their natal tube, climb onto the surrounding vegetation, and then disperse by a form of ballooning. They will make their first tube before night falls. They won't reach maturity until they are 3-4 years old. The female may rear another brood in her life, which could reach 7-8 years or longer.

Habitat specialists
Individual longevity and slow development means this species is sensitive to habitat changes, as adult individuals don't move from their tube once settled. They live in undisturbed open habitats, on south-facing slopes of sand or friable soils with sparse vegetation of trees and or heather, either inland or coastal, often under the protection of rocky outcrops, anthills or bushes. Although the purse-web spider can be found at high densities, it is a scarce, very local species. Given that a population has recently been discovered at a Yorkshire site (the first record for Yorkshire), it is possible that, due to their secretive habits, some populations of this species still remain to be discovered.

More information
Enock, F. 1885. IX. The life-history of Atypus piceus, Sulz. Transactions of The Royal Entomological Society of London, 33, 389-420. Available from the Biodiversity Heritage Library here. This, according to Bristowe, is the only account of a spider natural history from the 19th century, it is a pleasure to read.

Tuesday, 20 October 2015

Oonopidae: Pink Prowlers

A medium sized family which includes spiders with six, four or two eyes, and even eyeless cave dwelling species. There are two British species of the genus Oonops, but also at least three other species introduced and now living in hot-houses. They are tiny pinkish spiders, up to 2 mm long. They have six eyes in a cluster, and are nocturnal wandering spiders that spend the day in a simple silk cell. They have a simple female genital opening and male palp. These spiders have a most peculiar way of moving, with a slow walk with front legs stretched out like feeling the ground, followed by a run at speed.

Under recorded
 Oonops domesticus, also called the Pink Prowler, is only found inside houses, but it does easily go unnoticed due to its nocturnal habits. Michael Roberts recommends getting up at 3 or 4 in the morning and checking the walls for the presence of this spider, adding 'By a strange coincidence my first sighting of O. domesticus in our present home was when illustrating the species, at 4 a.m., and it ran across the illustration!'. A more civilised alternative is to search for the outdoors species, O. pulcher under rocks and bark or in bird nests or dry leaf litter. O. pulcher is often associated to the webs of larger spiders, like Amaurobius and Tegenaria. There it acts as a scavenger, feeding on the discarder remains of their prey. A further indication of how under recorded these tiny spiders are, is this confession by William Bristowe:

 'three species which I had added to the British list - Oonops domesticus, Euophrys lanigera and Physocyclus simoni were subsequently found in the British Museum (Natural History)! May I be forgiven for disclosing this secret.'

Small brood
They hold the record of fewest eggs per brood, just two, which are laid in the mothers cell in a transparent egg sac.

UPDATE 20/09/16. Post now includes a photo of a Oonops (likely domesticus) that walked on my office wall while I was working, my first sighting of these spiders.

Monday, 19 October 2015

Mimetidae: Pirate spiders

This is a small, but fascinating spider family. It comprises just 4 species of the genus Ero, two of them common and widespread.  They are small spiders, about 5 mm long, with globular abdomens, which have two or four tubercles. They have annulated legs, the first pair endowed with a series of spines.

Spider eaters
The Mimetidae are specialists in eating web-building spiders. Ero does not build a proper hunting web, it is a nomadic species which wanders in search of webs. Once found, she may invade the web, and then pluck it with her front legs. The owner might come to investigate, as it would do if an insect had fallen in, but then Ero will quickly grab and bite one of the spiders legs. The venom is quickly acting and then Ero will feed on the spider. In occasions the web owner might be able to escape minus a leg

Stalked egg sacs
Female pirate spiders produce characteristic egg sacs, which are more noticeable than the spiders themselves. They have a long stalk and are covered on coarse, brown wavy silk, presumable for protection, as the female takes no care of the egg sac or the spiderlings themselves.

These two photos are the only ones I have possibly portraying a Ero cambridgei/furcaca female sitting on a flower in a bush, legs withdrawn.

Sunday, 18 October 2015

Segestriidae: Tube dwelling spiders


This is a small spider family of which only three species of the genus Segestria are found in Britain, only one of them widely distributed. They are elongated spiders, with only six eyes and the first three pairs of legs facing forward. They have a characteristic dark abdominal pattern, reminiscent of an adder's. They live in silk tubes in cracks in logs, walls, under stones and cliff faces. The tube opening is surrounded by at least six radial threads extending quite a way away, which act as signal threads to the spider sitting inside the funnel and are quite characteristic of the genus. The spider is active at night, when she comes out to her retreat's entrance, poised with her forward facing six legs touching the radial lines, awaiting passing insects.
Green fangs
Segestria florentina (top photo taken in Sheerness, Kent, courtesy of Robert Jaques) is a large spider that can reach 22 mm of body length. It is almost black with iridescent green chelicers. It lives near sea ports and it is thought to have been introduced from at least the 19th century with produce from the Mediterranean, from where it is native.

Maternal care
The female makes her egg sac inside her retreat and remains with her spiderlings until they disperse. Matriphagy, where the mother dies and the spiderlings eat her, has also been reported.

Saturday, 17 October 2015

Salticidae: Jumping spiders



Salticidae is the largest spider family of the world, and easily the most charismatic. Their large frontal eyes and visually driven behaviour makes them instantly likeable. They are mostly diurnal and have a preference for sunny, warm habitats, which means it is not so well represented in the UK. There are just 36 species, most of them in the south and many very locally distributed. Jumping spiders are also easily recognisable for their eye pattern: four eyes facing forward, the central two much larger than the others. Jumping spiders move in a distinctive way, with sudden runs forward and frequent stops, when they orient their cephalothorax ostensibly to look around. They jump very well, and do to do so in a controlled way (unlike grasshoppers and fleas, which can jump longer distances), always securing a drag line just before each jump. Silk is used as safety lines and also to weave a sac for resting.

Visual spiders
Jumping spiders are the arthropods with the best visual sense. Their large anteromedian eyes are responsible for their visual acuity, while the remaining six eyes act as motion detectors. The lens of the eye is part of the cuticle and is fixed, but the eye tube orientation is controlled by six pairs of muscles. They have an additional internal lens in their eyes, which together with the detailed configuration of the retina makes them work like miniature telephoto lenses. Their acute visual sense is used during hunting, to locate prey often at remarkable distances. They can approach prey taking a detour, instead that on a straight line, and when they are close to the prey they stalk it before jumping on it. They can also use a sit-and-wait strategy, constantly scanning the environment visually.

A male Salticus scenicus with a house fly prey.
Female Salticus scenicus with prey, probably an aphid.

Semaphore courtship
Salticids have colour vision, even in the ultraviolet. This explains why some species are so strikingly colourful - often with iridescent scales or cuticle. Males have often more colourful palps, front legs, chelicers and the area around the eyes, and these features are used during courtship. They use a combination of visual and auditory cues (drumming) during courtship, which can incude chelicer opening, abdomen drumming and palp waving, often in a mesmerising, balletic routine, which the females watch attentively. I really recommend watching the fantastic collection of videos of the Australian Peacock spiders by Jurgen Otto, which have taken spider courtship to its most dazzling extremes. The stripped black and white Salticus scenicus or Zebra Spider, is widespread in the UK. In this species the most obvious difference between males and females is the size of the chelicers, which are massive in the males, and are used for sparring (watch this short clip of two males sizing each other up), but their courtship is not the most complex. The males raise their front legs and open and close the chelicers in front of the female, but they also chase females into their retreats, where mating often happens.


Male Salticus scenicus. Note the long black chelicers with the palps over them (look at the female on the top shot for comparison).

Synanthropic species
The tiny Pseudeuophrys lanigera seems to have a preference for buildings and roofs. I have found it inside my office and lab a few times, and once on my house wall. It is probably very under-recorded due to its small size (5 mm).   
 
Female Pseudeuophrys lanigera.
Pseudeuophrys lanigera, note the white palps and moustache, red markings around its eyes and dark shiny front legs

Another human-associated salticid in the UK is Hasanius adansoni. A tropical species in origin that has expanded across the world to occupy buildings in warmer areas or heated glasshouses in cooler climes. In the UK, there are records from the early 1900s, and it has been found in Kew Gardens, the Eden Project, and the Royal Botanical Garden at Edinburgh, amongst other places. In Edinburgh, it is likely there has been a colony for over a hundred years. The following photos were taken in a garden in Mallorca. Males and females are strikingly different, the male is darker with white stripes at the front of the abdomen and palps. red 'goggles' and black front legs. The female is very pale, with a yellow face.
Male Hasarius adansoni.
Female Hasarius adansoni.
Ant mimicry
Three genera are very convincing ant mimics, moving and looking like ants. Myrmarachne has a raised front of the cephalothorax, which gives an impression of the ant's head. Some have constrictions in the abdomen and the colour patterns further disguise the presence of eight legs. The ant mimics are quite scarce and local here where they reach the limits of their distribution, but are much more numerous in the tropics.

Friday, 16 October 2015

Thomisidae: Crab spiders



This family is closely related to the running crab spiders Philodromidae. There are 26 British species. They are broad-bodied, with the front two pair of legs are much longer and stouter that the others and furnished with stout spines, which they often hold wide open in a manner similar to the way a crab hold its front legs open defensively. This, together with their widely spaced eyes placed on tubercles and their ability to walk sideways has given them their common name. There can be substantial colour and size polymorphism, with smaller and more cryptically coloured males.

Ambush predators on flowers
Crab spiders do not build a hunting web. Many species of crab spiders use a sit-and-wait strategy to hunt insects. They sit on a flower immobile, front legs open and rear legs holding them to the substrate, relying on their cryptic colours to avoid being seen by visiting pollinating insects (top shot shows Misumena vatia. Credit: Alan Shearman, CC BY-NC-SA 2.0). As soon as an insect lands on the flower the spider will swiftly bite it catch it. Other species can also stalk prey, cat style, while on the ground, or low vegetation. More on a BugBlog post here.
Xysticus cristatus stalking a fly.
Xysticus cristatus on dandelion, using the sit-and-wait strategy.

Colour changes
Crab spiders are very diverse in shape and colour and some species are very colourful, but yet, remarkably camouflaged in their habitats. Some species, such as Misumena vatia are able to slowly change colour to match the flower where they are sitting. Adults can change colour from yellow to white or greenish with or without pink lateral markings, and most of the time it matches the colour of the flower it is sitting on.

Female Xysticus cristatus
Male Xysticus cristatus

Thursday, 15 October 2015

Theridiidae: Cobweb weavers

A large spider family, including some very famous world spiders such as the North American black widows (Latrodectus sp.), the Happyface spider (Theridion grallator) and the social spider (Anelosimus sp.). The 56 British species are small to medium spiders. They make irregular webs of criss-crossed threads with some of them stretched and loaded on one end with sticky dropplets, which break when an insect struggles to break free and lift the prey in the air like snares. The genus Episinus, however, produce the most remarkably simplified web, a 'H' shaped with four sticky threads connecting the spider to the ground and an over head support. Theridids have a relatively large, well marked abdomen with a diversity of patterns and colours.  This family includes one of the most fascinating examples of maternal care in spiders.

Powerful hunters
These spiders are able to throw sticky threads over prey to immobilise them. This ability, and their rapidly acting venom, makes them formidable hunters able to subdue much larger prey.
Steatoda bipunctata with immobilised Ectemnius wasp
Even the powerful and agressive male Anthidium manicatum couldn't escape Enoplognatha sp.
A wasp? No problem for Enoplognatha
Not even a honeybee. Note the typical web of Enoplognatha, tangled around a flower, ready to catch visiting insects, with the spider neatly hidden under the flower itself.
Enoplognatha doesn't even care about the chemical secretions of shieldbugs.

Colour polymorphism
Enoplognata  comes in several colour morphs. There is a white morph and one with a pink stripe. This is the pretty and rarer pink morph.


Stridulating males
Steatoda bipunctata males have a serration at the end of the cephalothorax which rubs against teeth at the front of the abdomen making an just audible stridulation which is used during courtship. In his field guide to the Spiders of Britain and Norther Europe, Michael Roberts writes:
I first heard this in use as a medical student. Quietly studying the anatomy of the brachial plexus, I became aware of a quiet sound from a guitar standing in the corner. My initial thought was that one of the well worn strings was very slightly creaking as if about to snap and I  clearly remember tensing myself for this not uncommon event. It turned out to be a pair of Steatoda bipunctata mating inside!
This is the male of Steatoda bipunctata. It waves it's large palps as it runs on the ground looking very ant-like. The female (top shot) has a look reminiscent of a fat tick, its cephalothorax almost hidden by her large, shiny abdomen.

Maternal care
Theridids make egg sacs that are attached to their web, or under a curled leaf retreat, and are often guarded by the females. Some species even carry the egg sacs attached to the spinners. The presence of females protects the eggs from predation, for example from ants. The mother will react to the presence of ants by relocating the egg sac more centrally on the web. Enopognatha guards her egg sac under a curled leaf and stays with the spiderlings until her death.
The small Theridion sisymphium female produces a bluish egg sac, which she guards. When the spiderlings emerge she will feed them  mouth to mouth with regurgitated food. Later, she will share prey with them until they are ready to disperse.
The wonderfully weird egg sac of Theridion pallens
The blue egg sac of Enoplognata sp.
The tiny Theridium pictum with her egg sac (note the screw head for scale). This species lives near other spiders webs and steals food from them. 
Enoplognatha with her brood inside a curled leaf.