Tag Archives: natural history

Raft Spider Life Cycle

Posted on by
Reply
Raft spider on pond surface

Raft spider on pond surface

You’d think that arachnids and water was an unhappy combination, but one species of European spider has made boggy ponds their home.

The raft spider (Dolomedes fimbriatus) is the UK’s largest native spider – its body growing up to 2cm long.

It uses the water’s surface like other spiders use their webs – feeling for the vibrations of potential prey with front legs extended. Using this technique it hunts tadpoles, insects and occasionally small fish:

Raft spider eating damselfly

Raft spider eating damselfly

When alarmed, the water repellent hairs on the raft spider’s legs enable it to dive beneath the water, trapping a bubble of air to keep it alive until the coast is clear and it cautiously re-emerges:

The wetland pools favoured by raft spiders are increasingly rare in this country. On the RSPB’s Arne reserve in Dorset their habitat is lovingly preserved, and offers wildlife watchers easy access from the nearby heathland trail:

Boggy pond habitat

Boggy pond habitat

On a good day dozens of raft spiders at various stages in their life cycle can be witnessed at the pond’s edge.

1. Sex

The female raft spider is often considerably larger than the male and mating is a dangerous business. He approaches her cautiously, waving his front legs tentatively to judge her receptiveness:

Male raft spider approaches female

Male raft spider approaches female at her den

She may rush out to scare him off on numerous occasions, after which she retreats and the process begins again, the male edging closer all the while. It’s a nerve jangling thing to watch, let alone participate in.

2. Birth

The female spins a silk bag to contain the fertilised eggs, which she carries about beneath her body, keeping it just warm and moist enough to ensure their survival:

Raft spider carrying egg sac

Raft spider carrying egg sac

Then, when the baby spiders are ready to hatch, she lashes the egg sac to vegetation at the edge of the pond and the tiny hatchlings emerge:

Baby raft spiders in nursery web

Baby raft spiders in nursery web

Mum typically lies in wait nearby to ensure that her young ones don’t come to any harm:

Raft spider guards her hatchlings

Raft spider guards her hatchlings

This phenomenon of hundreds of spiderlings crowded together for their own mutual safety is only really appreciated up close:

Raft spider hatchlings

Raft spider hatchlings closeup

But soon the young raft spiders are large enough to fend for themselves and disperse around the pond.

3. Death

Raft spiders are not fussy eaters. When times are tough and food is scarce, or when too many raft spiders compete for the same local resources, they may even turn to cannibalism:

Not such a pretty sight!

Related links:

Surrey Glow Worm Quest

Posted on by
2

If you’re looking for a photographic challenge then wildlife macro at night is guaranteed to keep you amused and frustrated in equal measure.

Glow worms (Lampyris noctiluca) come equipped with their own bioluminescent light source, and with a bit of research shouldn’t be too difficult to locate in the right environment. But in the dark simple tasks become considerably more complicated.

These ‘worms’ are in fact a beetle. On summer nights the flightless female glow worm climbs a grass stem,, or other vegetation, and emits a bright chemical light from her lower abdomen. This luminous display attracts the flighted male glow worm and mating begins, at which point the happy couple turn out the light and retire to bed together in the undergrowth.

In the UK glow worm numbers – or at least the number of people reporting them – have diminished over the years. Light pollution from sprawling urban areas may be one reason for this, as the female doesn’t like competition, and seeks out the darkest rural recesses in which to display to potential mates. The inexorable rise of the motorcar has also meant fewer people traversing the countyside on foot at night, and so less likelihood of happening across these creatures. Modern use of pesticides may also have played a part.

The wilds of South Dorset proved good hunting grounds for me last year and I was keen to have another crack at this subject in Surrey over the summer.

Sleeping Beauty

Sleeping Beauty: Dorset glow worm (Lampyris noctiluca)

Initial research turned up not much however. Almost every contact I quizzed looked at me with bafflement and a little wonder when I enquired about glow worms in the county, as if they’d become semi-mythical beasts in this stretch of the London commuter belt. A bit of Googling turned up a handful of vague mentions and precious few images.

The excellent UK Glow Worm Survey website, run by the extremely dedicated Mr Robin Scagell, offered more precise records and this especially tantalising glimpse of days gone by:

Box Hill, nr. Burford Bridge, Whole slope of Hill covered with glow-worms, summer 1915

Promising, but a long shot more than 90 years later perhaps. Then a chance meeting with a twitcher confirmed glow worms sighted in a very specific area of the hillside in the 1980s and the balance of probabilities swung in favour of action!

From my vantage point atop the steep chalk slope of Box Hill the sun began to set impressively, and the exhausting vertical scramble required to get there faded into memory.

Tight security in preparation for the Olympic cycle race meant that the entire National Trust property was ringed with high steel barriers. A checkpoint restricted traffic up the narrow zig-zagging road to the top, and guards with walkie-talkies patrolled its length. The pedestrian gates thankfully remained open.

Dorking at night

Town of Dorking in Surrey from Box Hill after dark

Bright lights from the dual-carriageway below continued to illuminate the entire downland slope after the sun had faded, which wasn’t promising. But in a deep, shady dip behind the ridge a twinkling greenish light in the grasses finally caught my eye.

In total 8 glowing females were located along a short stretch of chalk track.

The first young lady was tucked well back into the shrubbery and inaccessible to my lens. The second was more exposed, on leaf litter near to the ground. With a bit of tripod gymnastics and some macro slider extension action I edged within range.

Glow Worm Filigree

Glow Worm Filigree: Surrey glow worm on leaf litter

In this shot the natural glow from the beetle was supplemented with indirect light from an LED torch off to one side. It’s a balancing act to expose the whole subject without drowning out the insect’s own subtle illumination.

The same creature on a long exposure without the artifical light source gives a quite different visual impression:

Glow Worm Limelight

Glow Worm Limelight: Glow worm (natural light)

More typically glow worms can be found in thick grass, clinging to the stems a short way up, and rotating their bottoms skyward as this next one was:

Glow Worm Jade

Glow Worm Jade: Glow worm in grass

Where the beetle is tightly surrounded by reflective surfaces the light she emits is magnified.

In all the above images the glow worm’s head is firmly concealed beneath her carapace, and this is usually the case I’ve found. But before I departed for the night another individual proved less coy.

Glow Worm Red Light

Glow Worm Red Light: Glow worm under red filter LED

In these circumstances a bright white light can disturb the beetle, which then turns tail and vanishes, which is no good for observing behaviour. So I used a red filter, hoping she would be less sensitive to light in this part of the spectrum. It appeared to work and she continued to clean her antennae for some while:

Related Links: