Monthly Archives: July 2019

Love is in the air.

The Norfolk Hawker dragonflies are all around us at Carlton at the moment. Big, brown and beautiful with jade green eyes, they often create a sudden rattling sound as their wings beat stems as they take off from amongst reeds. It’s like being in the midst of a bunch of tiny croupiers mixing packs of cards.

Handsome beasts!

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A mating pair of Norfolk Hawkers

In this pic the male is above, clasping the neck of the female with his claspers, which fit into special grooves on her neck, specific to species -a key and lock system which may have evolved to prevent successful mating between species.

He has already successfully driven off competing males and attracted her to his territory, and has already transferred sperm from his primary genital opening on the 9th abdominal segment. near the tail end of the abdomen, to his secondary genitalia at the second and third abdominal segments, nearer the thorax.

If the female is ready, she will curl her abdomen under and forward to bring her genitalia into contact with the male’s secondary genitalia, allowing the transfer of sperm and insemination.

After the initial clasping, the pair may fly together till the male finds a perch to cling on to. The shape they make is called the “heart” or “wheel”. After mating, the female needs to lay her eggs, but before this the male may fly with her, still clasped, to prevent other males mating with her. He may also spend some time cleaning out her genitalia with his penis to remove any possible sperm from rivals.

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Here the female is depositing her eggs (ovipositing) on a stem of vegetation. This is a very vulnerable time as she is at risk from predators such as fish or fen raft spiders. The method of ovipositing varies between species. Some possess a sharp ovipositor used to slit vegetation so the eggs can be deposited inside, others lay eggs in the water and some drop them in flight.

Although the shot below is rather poorly focussed, I wanted to include it and the series below as it shows a pair of damsel flies after mating. The male is clasping the female and took off and landed in different places several times. Every time they landed she oviposited.

When I get a chance to take better shots I’ll replace these -but I was thrilled to get a chance to witness this -just the day after writing the main part of this post.

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About the Behavioural Studies

I’ve been asked by Dr Helen Smith, the UK’s leading authority on the Fen Raft Spider, to help her answer questions she has about the Fen Raft Spider. Our starting point is observing behaviour. What this means for me is to sit in the blissful peace and tranquillity of Carlton Marshes in a chair, with binoculars, camera and notebook, and simply watch a nursery web and/or and adult spider, and observe, and note. My main job is to report the “how” of Fen Raft Spider behaviour, and where I can, I may make a suggestion or two along the way about the “why”.

The following posts will attempt to be factual and objective reporting, so I’m not attempting to provide a literary read. But some of you may find the information interesting.

Neither of us have any clear idea of where this will lead, or indeed if I’m able to contribute at all to the sum of knowledge around this beautiful and sophisticated animal. But I’m going to have a go!

Thank you for getting this far with me. Please stay on the journey.

Study 1

Fen Raft Spider behavioural study record 001

NB This is the first session and as such was experimental to assess what to record and how to record it. The template on which this record is based was developed subsequently, hence not all fields are complete for the first few records

Location:                                                         Carlton Marshes: Dyke 10

Date:                                                                 02/07/19

Time start:                                                      11.00

Time finish:                                                    12.50

Weather (from BBC weather app):

  • General:                            Fair mild day
  • Humidity:                         –
  • Pressure:                           –
  • Temp:                                18C
  • Temp feels like:                –
  • Wind:                                 Gentle breeze
  • Cloud cover/sun:              Intermittent sunshine and broken cumulus cloud

Observational subject:

Nursery web

Observations:

Web amongst sedge, 18 inches off water in margin. 5m south of 10mph sign. A recently opened egg sac was reported seen on 29/06/19 -three days before this observation. No adult seen. Egg sac present, only two spiderlings seen crawling about web and on sac. Became more active when sun came out.

Impression is that the web is looking tatty -there were some strong breezes in in the area in the three days before this record.

12.05: Little activity

12.50: No further observations to make. Ended.

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Study 2

Fen Raft Spider behavioural study record 002

 

Location:  Carlton Marshes: Dyke 10, immediately by northernmost red and white verge marker post

Date:                                                  08.07.19

Time start:                                        14.00

Time finish:                                      16.10

Weather (from BBC weather app):

  • General:                Mild day, breezy
  • Humidity:              –
  • Pressure:                –
  • Temp:                     17.5C
  • Temp feels like:     –
  • Wind:                      Moderate breeze
  • Cloud cover/sun:   Intermittent cloud, mostly sunny

Subject:

Nursery web with spiderlings. No adult seen.

Vegetation/macro location:

Web in sedge, about 12 inches above water, in margin.

Observations:

The web in study 01 can no longer be seen. This web is further south along the same dyke.

14.00. Spiderlings in a torus formation, the right-hand half shaded, the left in sunlight. Bursts of activity noted in two forms: one as a cascade spreading over the surface of the huddle of spiderlings, the other as a simultaneous burst of activity all over the surface, with individuals at separate points around the huddle simultaneously starting movement. Does this suggest different stimuli for activity? There was no visible trigger for the activity, which always settled down within a few seconds.

14.45. Longer spells of sunlight on web and increased frequency of bursts of activity noted during this period.

14.50. Several bursts of activity occurring within the space of one minute but lasting only a few seconds. These bursts were in the simultaneous pattern.

15.00. It is possible to see now from a different viewpoint that the torus is in fact two separate balls of spiderlings. Learning point: get several viewpoints where possible.

15.30. There are in fact three balls of spiderlings, with one to the left of the others, shaded and well hidden under a broad sedge leaf. The other two are now both unshaded and bursts of activity are noted in both, when the sun emerges. The balls are beginning to join up.

15.55. Sunlight now continuous as clouds have broken up. The two right hand balls have coalesced to form a crescent concave upwards, approximately facing the direction of the sunlight. More a radio telescope shape than a lens shape.

Observed formation shape change consistent with basking behaviour to increase body temperature. This would increase metabolic rate and consequently growth rate.

Increased activity during periods of sunlight consistent with increased metabolic rate and muscular activity with increased body temperature.

Stimuli for activity bursts not known.

16.10 End.

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The hidden third noted ball of spiderlings on the left, shaded by a sedge leaf. The next two are visible and partly obscured.

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Same view closer in and a little later.

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Crescent formation

Study 3

Fen Raft Spider behavioural study record 003

 

Location:                                           Carlton Marshes: Dyke 10. Same as in Study 002.

Date:                                                   09.07.19

Time start:                                        11.30

Time finish:                                      12.15

Weather (from BBC weather app):

  • General:                   Cool slight breeze
  • Humidity:                74%
  • Pressure:                 1022 KPa
  • Temp:                       15C
  • Temp feels like:       –
  • Wind:                        S, 7mph
  • Cloud cover/sun:    Cloudy

Observational subject:

Same web as in 002.

Vegetation/macro location:

As before

Observations:

11.30. Web looks thinner and scantier since seen 18 hours previously. Volume taken by spiderlings seems less, suggesting either less spiderlings or that they are huddling more tightly. Two formations seen, a vertical sausage shape and a separate small ball. Both have a reduced surface area to volume ratio compared with the more diffuse shape of yesterday. No adult seen, very little activity indeed compared with yesterday.

Formation consistent with heat conservation.

12.15: No further activity noted and as I was getting cold (being unable to rapidly reduce my surface area to volume ratio), study ended.

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Study 4

Fen Raft Spider behavioural study record 004

 

Location:                                           Carlton Marshes: Dyke 5b, 8m South of bridge

Date:                                                   16.07.19

Time start:                                        14.00

Time finish:                                      15.45

Weather (from BBC weather app):

  • General:                  Sunny intervals and light winds. Feeling very warm.
  • Humidity:               58%
  • Pressure:                 1018 mb
  • Temp:                       21C
  • Temp feels like:      25C
  • Wind:                       N, 6mph
  • Cloud cover/sun:    V sunny with occasional cloud cover

Observational subject:

2 Balls of spiderlings in a nursery web with egg sac, adult beneath

 

Vegetation/macro location:

Web and spiderlings about 30cm above water surface in water soldier about 1m from east bank. Adult sitting on frogbit on water surface immediately beneath web.

Observations:

14.00. Dark unbanded adult female present

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Initially 2 balls of spiderlings seen in web. Little activity at this time.

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14.20. Adult has moved away from me to next frogbit pad. Can only see back of abdomen and spinnarets. Contrasting light and obscuring leaf cover prevent photo.

14.40 has turned around and is facing me

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15.00. Spiderlings have coalesced into a lens shape roughly facing the direction of the sunlight

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15.40. Spiderlings noted to be very active in full sun

 

Lens formation and increased activity consistent with increased exposure to warmth from sunlight. Suggests active basking behaviour in spiderlings. No active movement of adult into sunlight does not support active basking behaviour in this individual during this study.

14.45 End.

Study 5

Fen Raft Spider observational study record 005

Location:                                           Carlton Marshes: several dykes

Date:                                                  23.7.19

Time start:                                        11.30

Time finish:                                      15.00

Weather (from BBC weather app):

  • General:                              Sunny and light winds. Feels hot
  • Humidity:                            58%
  • Pressure:                            1018 mb
  • Temp:                                  22C
  • Temp feels like:                25C
  • Wind:                                  N 6mph
  • Cloud cover/sun:              clear sky

Observational subject:

My aim today was to observe adult spiders. Only 4 days ago on a routine survey we found 38 webs and maybe a dozen adults. Today on a very hot day, circumnavigating most of the survey-allocated Dykes at Carlton across 3 hours,  I saw only maybe 8 of those webs, most looking tattered, and only one adult, in a deeply shaded recess in the margin, under vegetation. Too dark and too distant even for a decent photo.

3 days ago we had storms and brief but torrential downpours. These would have damaged or destroyed many of the webs we had seen on the routine survey. After speaking to a biology graduate friend, I understand that spiders tend to shelter in the cool in hot weather, and are prone to desiccation in such conditions. Maybe the FRS adults had all gone into the shade, or perhaps underwater. There was no sign of guarding adults in the very few webs with spiderlings present that I saw today.

Vegetation/macro location:

N/A

Observations:

It seems reasonable to conclude that the storms followed by hot weather affected my ability to find viable nursery webs and provides explanation for the apparent absence of adults.

Courtship and Defence

Here is a selection of fascinating photos taken while on a routine nursery web survey. Whilst not a formal behavioural study in the sense of the others written up here, it is worth including here as the most appropriate section overall.

I can’t take credit for the interpretation of the pics and videos -I sent them to Dr Helen Smith who kindly interpreted them for me. These are mostly her words:

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Though this individual is not behaving in any particular way, we were interested to know more about the brightness of its bands which we found striking. He appears to have lost his second left leg. There is also a recorded conversation about its age in a courtship video below -Helen comments on this too.

“Band colour and brightness varies between individuals and is not particularly age-related. The exceptions to this are (1) that tiny juveniles tend to have lighter ground colours and (2) adult females tend to have more subdued band colours, although you do see some brightly banded ones. I’d be interested in trying to quantify the latter!”

“Re the overheard conversation backing this video, this year’s juveniles will only be a max of 3 weeks old and a very few mm long – you’re unlikely even to notice them and they’ll mainly be in the marginal vegetation rather than on the water. Anything vaguely ‘middle sized at the moment will be from last year’s broods.”

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“This couple are indeed a courting pair – the female is already quite gravid. The bobbing in the video is part and parcel of the courtship communication – both sexes do it. In the male it only signals intention but in the female, done (I guess) at a particular frequency or intensity. it can also signal lack of interest! Subtle stuff.”

Here is a nursery web (top right) and below and to the left is a spider. Try and spot it. If you can’t the answer is at the end of this post.

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Here he is -and it’s a male. He has a slim abdomen and clubbed palps like boxing gloves -these contain sperm, ready to inseminate the female, facing him. You can see her legs between the two sedge leaves forming a triangle.

About the above videos (of the same pair of spiders as in the stills), Helen says: “This shows another courtship sequence with the male doing the classic leg-tapping to create concentric waves that signal intention to the female. This can be a very protracted business and the fact that she moved away doesn’t necessarily mean that she’s not interested and won’t accept him in the end.” Apologies for the extra noise -no one was aware I was recording!

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This shot shows a female guarding her nursery. Her body is quite thin because she’s hardly eaten for weeks while carrying her egg sac but her palps are straight and not clubbed as a male’s would be.

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Here the same female is being defensive and guarding her nursery. You can see one of her palps very clearly – and it’s straight, not clubbed at the end. Apologies for the focus -not a lot of control with the apparatus -my camera battery had run out and I used a camera phone held only about 18 inches away, so she had detected my presence. She is holding her right first two legs in a V-sign -very appropriate!

Answer to the spotting question: He’s at the bottom of the photo, to the right of the triangle formed by the two most right hand sedge leaves. In the apex of that triangle you can partly see a female facing him.

Mother and child

The Fen Raft Spider displays a remarkable degree of maternal protective behaviour. the fact that many higher animals (for example reptiles) show no protective behaviour for their young as soon as egg laying is over makes this all the more remarkable.

The following pictures were taken whilst on a routine survey of the Carlton dykes in mid July 2019.

The next three show two females carrying egg sacs. The first two pics are of the same lady, the third is a different individual.

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She has wrapped her eggs in a silk cocoon which has turned a brown colour due to oxidation. She will carry them like this until they are ready to hatch. Then she will build a nursery web for them and help them out of the sac by picking a hole in the silk.

 

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Here’s a ball of hatched spiderlings in a (fairly thin) nursery web

 

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Mum guarding the nursery. You can see two balls of spiderlings in the web above her.

 

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Another mum with her nursery. She has a thin abdomen and could be mistaken for a male, but the non-clubbed palps give away her gender. She has eaten very little for weeks, being too busy carrying the sac, and guarding the nursery to hunt. This is on top of the massive energy expenditure in creating her young, the egg sac, and the web. Slimming World could learn a thing or two from her. It has just rained. Spider surveyors are a dedicated bunch!

 

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Here are a few spiderlings on the move within the web.

 

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This is a male. I’ve included the pic only because it displays so beautifully how the fen raft spider is perfectly adapted to aquatic life -walking on water. His first left and right legs are resting on the water, feeling for vibrations in the meniscus, possibly signalling the arrival of the next meal.

 

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Another male -see his clubbed palps in front of him -the “boxing gloves”. These are full of sperm transferred from his primary genitalia and stored ready for mating. The shot is slightly fuzzy as I’ve enlarged it considerably to show his eyes and the palps. He has uncommonly bright bands and you can see his two rows of eyes at the front of the cephalothorax (combined head and chest).

Males don’t have anything to do with the nurseries or young -they are basically sperm donors in their world. I have included this shot not because it’s particularly good, but because it took me ages to get the view and exposure I wanted, He was in a relatively dark recess at a distance. I sweated over it!