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.

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).

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.

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.

Why are common bumblebees common?

Six species of bumblebees in the UK buck the trend for population declines in other species. Of the 25 species of bumblebees, 3 are considered extinct, and a few others are restricted to a few sites. The common six (with the Tree Bumblebee soon set to become a 7th), however, are widespread and often very abundant in gardens. Why is that given how similar bumblebees are? All species have similar life cycles, feed on nectar and pollen and most lack specific habitat requirements. Their morphology is also remarkably similar, with the most important differences being tongue length (associated to head shape) and body size.

Species	Tongue length (mm)	Season
B. pratorum	7.3	Early
B. lucorum	7.5	Early
B. terrestris	7.6	Early
B. lapidarius	7.7	Middle
B. pascuorum	8.5	Middle
B. hortorum	12.5	Middle

 Do these differences reflect different foraging preferences? Foraging preferences might be very apparent to gardeners, with some species having a strong preference for a particular plant. For example only Bombus hortorum (above, on Phlomis) and Bombus pascuorum, the two species with the longest tongue, visit foxgloves. Surprisingly, bumblebee foraging preferences were not known until recently, when Goulson and colleagues studied the foraging preferences of most UK bumblebee species on a number of sites on South England, Scotland and New Zealand (where several species were introduced at the end of the 19th century).
The first interesting result they found is that pollen and nectar was collected by bumblebees from a different array of plants. Fabaceae (bean family) was preferred both for pollen and nectar collection whereas asteraceae was very used for nectar collecting but rarely for pollen. This could indicate differences in pollen quality amongst plant families.

When investigating the differences between common and rare species, pollen use was most important. A group of species are Fabaceae pollen collecting specialists, and others are heath specialists. Common species appear in the middle of the plot, indicating less specialisation and broader diets.
Goulson and collaborators suggest that the abundance of B. hortorum, a relatively specialised, long-tongued species, could be due to there being ecological space for only a single species specialised on long-corolla species given the declining numbers of long-corolla species in the countryside.
Emergence time was also correlated with rarity. The common six are all either early species or mid season species. Late emerging species seem to have suffered disproportionately. These late species are medium or long tongued and they appear late as they feed on unimproved grasslands (hay meadows for example), and this is a declining habitat in the last decades. In the paper they discuss that the loss of these habitats increased when vehicles replaced horses as means of transport and the decline of bumblebee species might be an unexpected legacy of the mechanisation of the countryside.

More information

Goulson, D., Hanley, M., Darvill, B., Ellis, J., & Knight, M. (2005). Causes of rarity in bumblebees Biological Conservation, 122 (1), 1-8 DOI: 10.1016/j.biocon.2004.06.017