Linyphiidae: sheet weavers and money spiders

Linyphidae is the largest spider family in the UK, with 270 species. Most of these are tiny, dark and and only identifiable with a microscope, the 'money spiders'. They typically build hammock-like webs held by a pattern of criss-crossing threads above and below. Liniphids usually hang upside down from their sheet web and do not use a retreat.
One of the largest species is the common Linyphia triangularis (above) whose webs hang in numbers from bushes in gardens and become very evident when covered in dew.

Neriene montana, is another large species (4-7 mm) common in gardens.

Stemonyphantes lineatus.

Gosammer and ballooning
These spiders can be incredibly numerous and active, and their drag silk threads can give fields a silvery shine, which is called gosammer. Money spiders disperse by ballooning. They climb up bushes and release a long silk line, which can get caught in the wind. Standing on tiptoes, the spiders are pulled up and lifted into the air.

Gossamer

A close-up of a gossamer-covered grass seed-head with money spiders ready to balloon.

Mating tactics
Linyphia has some interesting mating tactics I have blogged about before. Males have large chelicerae they use to fight other males while they guard a female.

Linyphia triangularis pair, the male is on the foreground. Males often sit on the female's web, mate guarding.

Money spider heads
Some money spiders have very unusual heads, with some of their eyes on top of turrets or humps (see if you can make sense of Walckenaeria!). These harbour glands that produce secretions, possibly nuptial gifts, during mating. Females of some species are known to hold the male's head during mating.

Egg sacs

Egg sacs are set near the web, and the females can sit on top of it guarding it.

Neriene montana near her translucent egg sac.

And now, ladies and gentlemen, spider sex!

I have seen spider courting behaviour on a few occasions, but the courtship was either too slow for me to watch the end of it, or the affair ended when the female captured the male and had him for lunch. Yesterday I was luckier, as I watched the common spider, Linyphia triangularis sequence of courtship and copulation. Let me warn you: spider sex is weird. Male spiders produce their sperm in testes inside their abdomen and insemination is internal, but instead of penises, they use their pedipalps - or palps - as an intromitent organ. This requires that before copulation takes place, the male transfers semen dropplets to reservoirs in his palps. This is a delicate operations: the male spins a tiny web and deposits a drop of semen onto it, then picking it up with the palps. Spider palps are a pair of modified appendages at the side of his mouth. In females and immature males, palps look like small legs. Once the male spider moults into adulthood, the palps appear fully developed, with a bulbous end and often a darker shade of colour than in the female. Palps have complex and diverse shapes, depending of the species, and are often used to identify male spiders. Palps have an additional function in some spiders, produce visual signal, as in jumping spiders and wolf spiders.
 Liniphya triangularis lives hanging belly up from its hammock-like web and courtship occurs at the end of summer, right after the female undergoes her final moult. The pair of Liniphia were actually mating when I saw them in a web in a Sedum plant, but a Siver Y moth disturbed them and they separated. The male then walked its way slowly across the web in search of the female. When he touched her, she moved a little further away, he then followed, touching her lightly every now and then. Once he faced her, she stayed still and accepted him by lowering her body at an angle, so that he could reach the underside of her abdomen, near the cephalothorax, where her genital opening is. He proceeded to insert one palp into her genital opening at a time, then the palp swelled as it locked with the females genital opening (above shot), and he removed it, appeared to lick it and then inserted the other palp. This was repeated on for quite a while as the male may need more than 100 intromissions to inseminate the female with two dropplets of sperm! The female was quite cooperative troughout and there were no signs of agression. She seems to touch the male's head with her chelicerae. Today they were still sharing the same web. Female normally only accepts a single male for copulation if he has completed sperm transfer, but this species has an alternative mating tactic in which smaller males interfere with mating and try and mate with the female (more here).
 I took two videos of the behaviour. The first one is a short sequence of the copulation itself, it the second, the pair, which has been disturbed, are separated and the male finds the female again and proceeds to carry on mating.





More information
Weldingh, Ditte Louise, Søren Toft, &; Ole Næsbye Larsen (2011). Mating duration and sperm precedence in the spider Linyphia triangularis Journal of Ethology, 61, 143-152 DOI: 10.1007/s10164-010-0237-x

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

Foggy morning

The fog painted the spider webs hanging from bushes and fences this morning with pearly dew drops. It made evident that at least three spider species are still active. On the photo an Araneus diadematus web, we also saw Zygiella x notata and Linyphia triangularis webs.

Courting spiders

I have posted on this common garden species, Linyphia triangularis courtship before, but I had the chance of observing this pair of spiders courting in the garden yesterday and take some photos. The male is larger, reddish, with an elongated abdomen and very large chelicerae. The female, at the back, has a rounded abdomen with a black and white pattern. As you can see in the bottom photo, there is a recent moult hanging from the web - I presume is the female's, as I cannot see the large chelicers of the male. In this species, the male does a form of mate guarding, sharing the female's web to wait until she has moulted and therefore she is ready for mating, and fending other approaching males off. The male vibrated its pedipalps and abdomen and slowly approached the female.

Spider chat up lines

In summer and autumn, spiders become more noticeable. The tiny spiderlings born in the spring have now become adults and males are wandering in search of females. One of the most common spider species in the UK is the elegantly marked Linyphia triangularis (female above). This spider makes a sheet web with criss-crossing silk lines over it in low bushes and trees. The spider hangs belly up from the underneath the sheet. Flying insects colliding with the transversal lines  fall onto the sheet, where the spider traps them. Yesterday, while photographing 7-spot ladybirds I came across a pair of L. triangularis. The male made jerky movements with its chelicerae and palps and the female replied.

Male (on the left) and female Linyphia triangularis. Note the male's large fangs on the bottom photo.

Unfortunately, I seemed to have disturbed them and the male retreated, so I didn't see the end of the interaction. Field experiments carried out by Nielsen and Toft showed that male L. triangularis use what are known as 'alternative mating tactics'. Males guard subadult females just prior to their final molt in order to access them while they are still virgin, possibly due to a strong sperm preference which results in males mating with a virgin female fathering most of the female's subsequent offspring. These researchers took advantage of this behaviour and took 56 males and paired them with females in the field. Once this relationship was established they introduced an 'intruder' and recorded what happened up to the point when the female was mated. In 64% of the cases, the males resolved the dispute about the female by fighting using their large chelicerae. Larger males are better at winning these direct conflicts. But in 36% of cases, males used a different strategy called 'interference'. After losing a fight, they hang around and 'distract' the courting pair trying to chase the winning male away from the web. They actually succeeded and mated the female first in 7 occasions (12% of all conflicts) showing that this strategy - which is adopted by small males - can pay off. Additional observations suggest that smaller males hang around and try and mate with the female (not virgin at this stage) probably winning some residual paternity in the process.

 In a different study, Funke and Huber carried out detailed measurements of males and females genitalia and cheliceae (see figure above) and found out that male chelicerae (including the oversized fangs) grow faster with body size than genitalia, indicating strong directional natural selection on this trait due to the large effect on male-male conflict in their fights for females.

More information
S. Funke and B. A. Huber (2005). Allometry of Genitalia and Fighting Structures in Linyphia triangularis (Araneae, Linyphiidae) Journal of Arachnology, 870-872 DOI: 10.1636/S04-16.1

Nielsen, N and Toft, S (1990). Alternative male mating strategies in Linyphia triangularis (Araneae, Linyphiidae). Acta Zoologica Fennica