Spiders in the Theridiidae family (comb-footed spiders, tangle-web spiders)

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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. They are usually brown, grey or black in colour, and have a row of comb-like bristles on their 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. Females usually have a round abdomen. Most females are venomous. Latrodectus mactans, the black widow On the left is a preserved specimen of Latrodectus mactans, the black widow in the Theridiidae family. 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

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. 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. 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

Enoplognatha ovata, 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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