Teridiidae carapace

Theridiidae family

These are also known as the comb-footed spiders or tangle-web spiders. There are around 2 200 species worldwide, and 76 species in Northern Europe.

Females usually have a round abdomen. Most females are venomous. Males tend to resemble females. They are usually brown, grey or black in colour, and have short and thin legs with a row of comb-like bristles on the hind legs, although this may be missing or reduced in small species.

Their web is irregular, three-dimensional and has sticky threads hanging from it to entrap prey.

Males court females by vibrating strands of her web with his legs of palps.

 
Latrodectus mactans, black widow spider, female

Latrodectus mactans, the black widow

Above left is a preserved specimen of and adult female Latrodectus mactans, the black widow in the Theridiidae family, and below is a drawing of a mating pair. It is native to North America, but there are other, very similar spiders in the Latrodectus genus:

  • in Chile (arana brava)
  • Argentina (arana del lino)
  • Mexico (arana capulina)
  • Australia (red back)
  • New Zealand (katipo)
  • South Africa (button spider)

In fact there are 30 species in the world, all similar in shape, and appearance.

The black widow builds its retreat in dark, sheltered spots, but builds its web for trapping prey between vegetation, and in most other places, even under stones. Unfortunately for humans, outdoor toilets are a favourite place, especially around the seat!

Usually it is found outside or in unheated buildings. It will only be found in heated buildings during cold spells, or prolonged rain. The adult female (above) is about 8 - 10 mm long and on the underside of the abdomen she usually has the characteristic red hourglass shape. The male is just 3 - 4 mm long, and his abdomen is elongated. The male does not bite humans.

Mating, reproduction and behaviour of the black widow spider

One mating can supply the female with enough sperm to last her a lifetime, and males are often, though not always, eaten after mating - it mainly depends on whether the female is well-fed or not. A male can tell if a female is well fed by touching her web with his feet, as he picks up scents through chemoreceptors in his feet. Given the choice of a hungry female and a well fed one, the male will always choose to mate with the well fed one as it is less likely that she will eat him afterwards. However if there is only a hungry female to mate with, the male is usually so desperate to mate that he will take his chances of escaping afterwards. Courtship can last hours, and consists mainly of the male wandering around the female's web tapping and plucking strands of silk and waving his legs in the air.

The drawing on the right shows a mating pair with the the male in black. The female lays around 400 eggs which hatch in 20 - 30 days. But cannibalism is rife among the spiderlings, and usually less than a dozen survive to meet the outside world.

In a good year a healthy female can produce around nine broods. Females are sexually mature at around 2 - 4 months. The average life span for a female is six months, and for a male, around three months.

The spider is timid and nocturnal. During the daylight it spends its time in the silken tunnel retreat. Generally when a female is on her web she will hang upside down.

Black widow venom and mode of action

The venom is neurotoxic, so it blocks the transmission of nerve impulses which leads to rigidity and cramp. It is said it is 15 times stronger than rattlesnake venom, but because of the small quantity injected it is not usually fatal to healthy humans on the rare occasions they are bitten, providing the bite is treated promptly and correctly.

Only about 0.5% of bites from the black widow to humans prove fatal. Strangely cats are very susceptible to the venom, but dogs are fairly resistant, as are sheep and rabbits

Black widow spiders mating
Enoplognatha ovata, mature female

Enoplognatha ovata (Theridion ovatum), the candy-stripe spider

Left is a mature female Enoplognatha ovata, Theridiidae, and on the right she has her eggs sac in which there are eggs or spiderlings.

Below is the typical method of hiding her egg sac under a bent leaf which is held in position by silk.

The female body length is 4 - 6 mm and the male is 3 - 5 mm. The colouring can vary with a cream or yellow abdomen with or without 2 red stripes or even one wide red band running down the middle, but they always have the black spots that can be seen in this specimen. They are usually found in vegetation.

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 Enoplognata ovata and egg sac
Enoplognata ovata egg sac hiding place
Steadota bipunctata, Coffee bean spider, underside

Steadota genus in northern Europe

There are 8 species in the Steadota genus in northern Europe. All have a thin white band around the front of the abdomen, but this cannot always be seen from above. Males and females are similar, but the males are smaller. The males can stridulate, and the sound is used during courtship. Females can live for over a year.

Steadota bipunctata, Coffee bean spider, Rabbit hutch spider

The female body length can be up to 7 mm and the male 5 mm (the scale on the right is in mm). They are common in the corners houses, outbuildings and also on tree trunks. This one was found on stacked firewood. Females can live for up to 4 years. They are sexually mature in the summer and autumn.

Steadota bipunctata, Coffee bean spider