Mothercare and nurseries in the spider world

Flanders Moss NNR

Over the last few weeks we have spent an awful lot of time starring at the bog surface as part of the Rannoch brindled beauty caterpillar project – see here and here. But the bonus is that it has been a chance to study other bog inhabitants as well. And some of the spiders have been particularly interesting.

Bethia wrote about some of the spiders of Flanders Moss here but in our caterpillar searches we came across 2 other species of interest. Knowing not very much about spiders I resorted to the British Spider Identification Group on Facebook. The page is run by extremely knowledgeable spider enthusiasts who very generously help others less gifted, in their identification of spiders of interest. You just post a picture with a request and await with interest. You can find out more here – https://www.facebook.com/groups/BritishSpiderIdentificationGroup

So first up was the nursery web spider – Pisaura mirablis.

The first thing you notice is a small silky tent tucked under protective twigs.

You can’t see much from above but by looking underneath you find the occupant. A female holding onto an egg sac.

Below – Here she is out of her silky tent carrying her egg sac.

The nursery web spider is not a rare species, though records in Scotland as more thinly scattered than down south. The female makes the silk tent to house the egg sac. Once the eggs hatch she stands guard over the tent while the small spiderlings live underneath. Soon the spiderlings start to disperse, weaving their own webs to catch small flies initially like fruit flies.

Mating in these spiders is a tricky business for the male. as during the mating process he is at risk of being attacked by the female. So to ease the situation he offers the female a nuptial gift. Once the female has bitten into his gift he moves around to mate with her while always keeping a leg on the gift to detect if she has either run off or going to attack him. Some males feign death at this stage of mating – his limbs become straight and he might be dragged around by the female. If the female stops still then he resurrects and continues with the mating. This “feigning death” is known as thanatosis and in nursery web spiders it can significantly increase the males chance of a successful copulation from 30% to 89%. It is probably best that I refrain from drawing parallel between this and human courtship.

Another spider that caught the eye was a Phylloneta sp. (we couldn’t identify it to species level because the are hard to identify from photographs but possible P. impressa or P. sisyphia.)

This spider, of which we saw all over the moss on the bog myrtle, is a member of the comb-footed spiders and is known as the mothercare spider. This is becuase the female goes beyond the call of duty in raising its young. .

The female creates an inverted cup of silk under which she puts an egg sac. Under that she spins a thick mesh of silk for catching prey which gives rise to another of its names – the tangle web spiders. When the spiderlings first hatch she regurgitates food for the youngsters but as they get bigger she shares caught prey. The female will die before the spiderlings leave the cup and her final contribution to their upbringing is that they will consume her. Now you can’t do anymore than that to raise your off-spring.

What I liked best about the silk cups was that the spiders wove leaves and twigs from the bog myrtle into the cup for better camouflage and maybe for keeping the weather off. But a careful look finds not only leaves but lots of insect remains also woven in. Everything from beetles to bugs to flies. I am not sure if this is a form of larder to make it easier to feed the youngsters or just a way of disguising the silk cup with leftovers.

Here is the silk cup seen from below and a female with her egg sac.

The tangled web can be seen here with other insect prey clustered around the cup.

A metallic blue beetle carapace incoreprated into the silk cup.

Another large beetle carcass attached to the silk cup.

Another metallic blue beetle carapace. Blue must be the in colour this year.

A fly amongst other prey helping in the construction of the silk cup.

Somewhere like Flanders moss is endlessly interesting. Despite working here on and off for over 20 years there are still so many new things to see and learn about. Sometimes all it takes is to look at a place in a different way, use a different method to observe what is around you and it opens up a whole new world. And once identified these highly evolved and complicated insect life histories are fascinating.