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.

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.

Gnaphosidae: ground spiders

This is a family with 33 British species, mainly comprised of agile nocturnal hunters who spend the day in a silken retreat. They are plain brown, black or grey and have short hairs that give them a shiny appearance. Some are powerfully built, large spiders. They have long, very mobile spinnerets, but unlike the Clubionidae they are divergent and the anterior pair is longer than the rest. They use them to weave their fine silk cells. One species, Scotophaeus blackwalli (above) is commonly found in the inside of houses, and can be surprised at night, when she prowls on walls in search of prey. Several genera have adopted a diurnal existence and evolved a remarkable ant-like appearance and behaviour. These are strikingly marked with spots and covered with iridescent scales.

Mate guarding and egg guarding
They mature in May of June, although the home-living Scotophaeus can mature all year round. Males often join immature females in their silk retreats until they reach maturity. The females will also make their white, often papery egg sacs inside the retreat.

Drassodes sp. pair. Males are often found together with penultimate instar females inside silken retreats. 

Scotophaeus occupying a cell in the bee hotel, guarding her egg sac.

Panthers of the invertebrate world

That's how William Bristowe described these spiders. They are indeed powerful, sleek, and nocturnal fighters. Their ability to produce sheaths of silk with their divergent spinnerets, which can move like fingers, gives them an advantage when facing other spiders. They can use these silk sheaths, coupled with their agility, to immobilise spiders larger than themselves. 

Scotophaeus blackwalli is able to prey on Pholcus, the other formidable spider predator in the house.

Male Scotophaeus blackwalli. It's spinnerets protruding at the end of his abdomen

Male Drassodes cupreus

Zelotes sp. found under log.

Ant mimics
The genus Micaria includes several species of ant mimics. Ant mimicry is actually very common in spiders and has evolved in several groups of spiders. The resemblance is often striking and specific to particular species of ants: the species on which these spiders prey (see this fantastic album of world ant mimic spiders by Alex Wild). In other cases the mimicry seems to have evolve in order to avoid predation. Micaria pulicaria can be taken for a Lasius niger garden ant. In sunny summer days when ants run on the ground, this small spider can be seen not only looking, but also behaving in the same way as ants, with front legs held up and quivering line the antennae of an ant. Micaria does not prey on ants, so from its resemblance to ants might give her a benefit of lower predation, allowing her to exploit the diurnal niche of small predators running in the open.

Micaria pulicaria, an ant mimic, which runs zigzagging across the ground rapidly, giving a remarkable ant impersonation.

Are male false widow spiders ant mimics?

An adult male Common False Widow spider, Steatoda bipunctata, barely half a cm in size, scuttled across the kitchen floor yesterday, most likely in search of receptive females. As most spiders, males look quite different from females, but these do look peculiar due to their very large palps, which they carry together while they walk. It immediately reminded me of a garden ant. I googled 'ant mimic Steatoda' and got nowhere, and my reference books also drew a blank, although they noted the relatively large male palps. How can you tell if a spider is an ant mimic (a myrmecomorph)? Sometimes it is so hard to tell them apart the myrmecomorph even tricks ants themselves - which the spider can then predate easily. Other myrmecomorphs are content to trick birds or other common spider predators which find ants distasteful, and the resemblance then might not be so striking on close inspection. There are several recognised ant-mimic spiders in the UK, which are likely to have evolved to resemble the ubiquitous garden ant Lasius niger, a small (4-5 mm), dark brown to black ant (see previous post on Micaria pulicaria). In that post I referred to a list of morphological features that ant-mimics are likely to have evolved, devised by Paula Cushing, so I can check if my candidate ant mimic male Steatoda bipunctata meets them:

1. Body shape: three body segments. Spiders have two body segments so ant-mimics must evoke the three body segments of an ant (head, thorax, abdomen) The large palps of male Steatoda bipunctata, carried raised and together, appear to make the role of an 'ant head'. Check!

2. Three pairs of legs and one pair of antennae. I need to carry more observations on live individuals to assess how the front legs are carried, as ant mimics carry them forward and often raised.

3. Petiole or 'waist' of the ant. My spider has a strong constriction at the end of the cephalothorax reminiscent of the 'waist' between the thorax and the abdomen of the ant. Check!

4. Mandibles. Pointed palps, but not an obvious feafure of Lasius niger.

5. Pair of compound eyes. No clearly mimicked, but also not a very distinctive feature of L. niger.

6. Sting. Not normally visible in Lasius niger.

7. Thin body and legs. Check!

8. Shiny surface. Very shiny, waxy looking. Check!

9. Segmented abdomen.  Abdomen with bands that reflect light as the tergites in an ant abdomen, with a similar pubescence. Check!

Not bad, a clear 5 out of 9 ant-mimic features clearly by this species, and I must add that something missing from the list are the general size and colour, which in this case also fit the garden ant. That the male does resemble an ant more than the female could be explained by the fact that he is likely to be exposed to predation while he moves in search of females - who sit on their webs and would be unlikely to gain much from resembling an ant.

What do you think? 

Ant Lasius niger tending aphid

Top view of male Steatoda bipunctata