Showing posts with label Steatoda bipunctata. Show all posts
Showing posts with label Steatoda bipunctata. Show all posts

Saturday, 15 September 2012

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

Sunday, 19 August 2012

Drama under the barbeque

This morning, while watching the hoverflies feeding on the fennel I realised I wasn't the only one interested in them. A female digger wasp Ectemnius, was poised on a cherry leaf, attentively following the action, and at one point the spotted a suitable hoverfly victim and attempted a capture.
 In the afternoon I came across Ectemnius again. Another female inspecting potential nest holes in a bee hotel, going in and out of them.
 I decided to sit and watch the action, faintly hoping the wasp would start digging a nest. I noticed the characteristic carded silk threads of Amaurobius spiders (top shot), and thought that spiders and digger wasps must come across each other with some frequency as female wasps inspect nesting sites. Then the wasp moved to the log pile under the BBQ and walked in and out amongst the logs. She appeared to have walked onto a silk thread and a false widow spider, Steatoda bipunctata, promptly came out of her refuge. A fight ensued, the wasp trying to bite or sting the spider, the spider spreading silk on the wasp and retreating, and repeating the procedure as the wasp became more and more entangled and buzzed intermitently in her futile attempts to get herself free.
 
The commotion got an Amaurobius out of her retreat, and at some point both spiders were attacking the wasp, although the Steatoda managed to secure it and, when the wasp stopped fighting, the spider cut free the threads that attached the prey to the log, and pull her to the safety of the retreat.
Early stages of the fight
The Amaurobius' legs are visible behind the abdomen of the wasp in the shot above, while the Steatoda secures the jaws of the wasp with more threads of silk
The wasp front end is now tightly wrapped on silk, now the spider focuses on the rear end
The spider drags the wasp to her retreat
 I watched all this with amazement and struggled to get decent photos as the action happened almost behind the log. The whole sequence of events happened within 15 minutes!

Sunday, 11 March 2012

Meet the common false-widow spider

The Common False Widow Spider, Steatoda bipunctata, is a regular species in or on buildings and gardens. The female (pictured) is a shiny chestnut brown. It is a small spider, up to 7 mm, with two black spots on top of the abdomen which give it its specific name. It is also known as Rabbit Hutch spider. The male has a much smaller abdomen. It is unrelated to the Widow Spider and not particularly venomous. We found this female in the folds of the cover of a tarpaulin outside, but I have found this species on the dry underside of logs, waterbut covers and window frames. Mature specimens are found all year round, surrounded by a web made up of a tangle of silk threads, some of which are sticky and held under tension so that struggling insects might break them and dangle from them. Males stridulate during courtship making an audible sound using a series of ridges in the abdomen which rub against teeth to the front of the caparace. Although native from Europe, the species was introduced in North America in the early 20th century and outcompetes the closely related species S. borealis.

More information
Spider and Harvestman Recording Scheme Website.

Martin Nyffeler, C. D. Dondale, J. H. Redner (1986) Evidence for displacement of a North American spider, Steatoda borealis (Hentz), by the European species S. bipunctata (Linnaeus) (Araneae: Theridiidae). Canadian Journal of Zoology, 1986, 64(4): 867-874, 10.1139/z86-130.

Thursday, 22 December 2011

Twelve bugs of Christmas

Today we woke up to a mild, sunny day and I was pleasantly surprised by the diversity of active bugs about. I made a count of species and when I got to twelve I was reminded of the traditional carol and made up a buggy version:

12 ladybirds walking | 11 winter-gnats dancing |10 honeybees buzzing |9 bluebottles basking | 8 leafhoppers leaping | 7 woodlice hiding | 6 hoverflies flying | 5 snails sleeping | 4 spiders weaving | 3 harlequins | 2 drone flies | and a bumblebee on ivy

The honeybees in the local wildlife garden were coming out tripping over each other and ladybirds (7 spots mostly but also harlequins and 22 spots) were awaken by the mild temperature. I counted 5 spider species outside (Tegenaria, Zygiella, Pholcus, Steatoda, Linyphia). The main surprise was the bumblebee worker, extremely fast and active and with pollen baskets full with pollen.

Here is a slideshow of bugs seen and photographed today

Tuesday, 27 July 2010

Queen ant makes spider dinner

I have come across queen garden ants (Lasius niger) for a week. The first one, a wingless one wandering on the garden checking every little crack on the cement eager to start digging her nest. She was quick and the light conditions weren't ideal, so, reluctantly, I moved her to a white bowl for a portrait (above). Yesterday, queens and males were emerging en masses from nests on the side of the street pavements in the afternoon, ready to start their nuptial flights.
The males are similar in size to workers, the queens, double their size and with a much larger abdomen.
Male garden ant
 I even got a mating pair, with the female dragging the male about and both flying away:
Mating ants (the male's antenna can be seen on the right hand side of the queen)
The queen ants will usually mate once in this flight and then land and dig their nests and live underground the rest of their long lives, the males will die shortly after. I say the queens, but I should have said the lucky queens. Most of them will actually die before they hit the ground again, eaten by swifts, swallows, gulls or sparrows. Others will contribute to a spider bonanza. Hundreds of aphids and some ants could be seen yesterday and today covering the webs of the missing sector spider (Zygiella x-notata) on railings. One queen wandered on my conservatory wall and fell on the disorganised cobweb of a Steatoda bipunctata spider, who quickly approached the ant (maybe biting it?) and retreated to the corner of its web. A few minutes later the queen had stopped struggling, and the spider came out for his dinner.
Steatoda bipunctata with dinner
The spider drags the queen ant to its retreat (notice the screw head for scale).