Steatoda Nobilis

Appearance

"Steatoda nobilis" has a brown bulbous abdomen with cream coloured markings that are often likened to the shape of a skull. Their legs are reddish-orange. Both female and male "S. nobilis" can be distinguished from other spiders of the same genus by their large size and typical colouration. Females range in size from about 9.5 to 14 mm in size, while males are 7 to 11 mm. The largest females are 13.7 mm in size, while the largest males can be 11.66mm in size. The males can be distinguished by their conformation of the palp and by their ventral abdominal markings. The females can be distinguished by their epigyne. The variation in size, shape and markings that have been observed is not thought to be due to location. Spiders found centimetres apart and siblings born from the same egg sac can look very different.

Male and female juvenile spiders are indistinguishable from each other.

Distribution

The spider is an introduced species across Europe, select parts of the United States and North Africa. Likely spreading. It was found for the first time in 2011 in Cologne, Germany. It is originally from the Canary Islands and Madeira. In England it has been reported mostly in southern counties, but its range was reported to be expanding northwards in the 21st century. In 2011, the spider was reported as an established invasive species in the USA, in Ventura County, California. In January 2016, it was reported that "Steatoda nobilis" had been found in Chile, the first time that the species had been recorded in the southern hemisphere. Research published in December 2018 showed that it was also established in Colombia and Ecuador. It is considered to be one of the world's most invasive species of spider. Seaside cities and villages with a temperate climate are especially favourable habitats for "S. nobilis".

The first recorded observation of "S. nobilis" in England dates back to 1879. The first recorded observation of "S. nobilis" in Ecuador was in 2014 at several locations as high as 2800 meters.

Between 1985 and 2010 there was no reporting of large numbers of "S. nobilis" anywhere, and scientists consider this to be a typical lag phase that is a phenomenon observed in many invasive species. Afterwards there was a large accelerated spread observed all over the globe.

They are able to establish in urban environments and build large populations in a short time.
The distribution of "Steatoda nobilis" is expected to increase northwards in the UK, due at least partly to mild winters in recent years. This prediction was reported by Stuart Hine of the Natural History Museum, and is substantiated by the National Recording Scheme.

The spider is reported to be an established species in Ireland. The first recorded sighting of the species occurred in the east of Ireland in Bray, Co. Wicklow in 1997.

Habitat

"S. nobilis" can be found year round, regardless of the climate, and they can be found both indoors and outdoors. They have been observed in a variety of different places from cacti and agave to roadside cuttings and buildings. They have also been found on telegraph poles, concrete fence posts, and ivy growing on walls. In Ireland they have been observed to be restricted to man-made habitats such as on steel, concrete or timber structures in urbanised area and not commonly found in forests or dunes. In another study conducted in Ireland, the adult spiders were exclusively only found on steel, concrete or timber structures in urban areas. In California they have also been observed in urban habitats but have also been observed to spread into natural habitats.

Juveniles are observed living in small crevices and holes, which can make their eradication difficult. In Dublin, juveniles have been observed on vegetation and leaves.

In Ireland, they were observed to be captured by common suburban spiders like the cellar spider or the lace-webbed spider.

Food

"Steatoda nobilis" uses an effective "attack wrap" strategy to immobilise would-be prey or predators, meaning that they are in close contact to their prey/predator. Prey is captured in typical theridiid fashion, where silk is wrapped around the victim using the spider’s fourth legs, allowing the spider to bite the victim. Their venom allows them to immobilise their prey by inducing paralysis. "S. nobilis" have been observed biting insects and spiders which causes a rapid reduction in motor function, most likely due to the release of venom. Their potent venom allows them to capture vertebrates much larger than themselves; the spider has been observed feeding on pipistrelle bats."S. nobilis" can eat both vertebrates and invertebrates. In Ireland, they were observed to eat woodlice. All of "S. nobilis"’s liquid requirements are observed to come from its prey. In laboratories they seem to thrive without water and in extremely dry conditions. In Ireland they have been observed to prey on protected reptile species. In southern England, an adult female was observed to haul up and digest a pygmy shrew ten times the spider's size.

Defense

Two thirds of the venom is composed of latrodectus-like toxins. Their venom is mainly composed of peptidase, serine protease, alpha latrotoxin and delta lactroinsectotoxin. Peptidase and serine protease are both pancreatic lipases and chitinases that help with digestion. Alpha-latrotoxin and delta latroinsectotoxin are toxins. About 49% of the venom is toxins, 15% are enzymes, 18% are proteins with other functions and 18% are proteins with unknown functions.

Alpha-latrotoxin works by creating a pore in the neurons and allowing an influx of Ca2+. This triggers an efflux of neurotransmitters, and once all the neurotransmitters leave, the signals between nerve and muscles are blocked. This leads to neuromuscular paralysis.

The venom of "S. nobilis" serves two functions: immobilisation of prey or predators and the predigestion of prey. The spider is able to efficiently and safely capture prey that are often much larger or stronger than themselves via the rapid paralysis and immobilisation tactic. Their venom is fast acting and can subdue both invertebrate and vertebrate prey. The range of enzymes in the venom suggest that the venom also functions to pre-digest the prey. One example is the enzyme Chitinase which can breakdown the exoskeleton of arthropods.