Notes on Misumena vatia

Harvard 2007. ISBN 0-674-02480-X or 978-0-674-02480-9

This book is a fascinating account of many years of research into Misumena vatia in Maine, U. S. A., and would be a very useful read for anyone interested in investigating the behaviour of this species in the U.K. (or elsewhere)

John Partridge has a copy which he would be willing to loan out.
 
Added by John Partridge at 15:48 on Sat 18th Feb 2012.

Misumena vatia - European Spider of the Year - the Queen of Bridge!
Observations on Bridging and Decision-making in Spiders by Christa Deeleman

From The Newsletter No. 108 March 2007

Introduction
Studies on ballooning have appeared frequently in arachnological literature. Recently, a comprehensive documentation of literature (Vander Borre et al., 2004) was devoted to that subject. Most experiments relate to observations of ballooning in open agricultural situations as a means of dispersal; there is far less discussion on bridging or spanning.

The number of publications about ballooning suggests that it is a much more common event than bridging. Ballooning is in the focus of attention, and it certainly is in the perception of those concerned with predators on various pests in agriculture, where dispersal of spiders is of vital interest.

Under circumstances when the air is humid and lit by near-horizontal sunrays, strands of very fine silk can be seen shining up between grass-stems, twigs and branches, and sometimes by the hundreds in a few square metres! When walking from my house to the letterbox along a lane bordered with shrubs and trees, I can feel the touch of invisible threads. For most spiders living among woody vegetation, bridging is the normal way of moving around, from branch to branch and from tree to tree.

Can a spider actually adapt its behaviour and choose between bridging and ballooning? This choice is probably most often dictated by the environment. In wooded environments, air movements are rarely directed upwards as opposed to open landscapes such as heather and grassland, where upward air streams are common. Indeed, most published observations of ballooning were from open landscapes: grasslands, fields, etc. and related to linyphiids, lycosids and dictynids which more often live in open habitats. Also, in woodland loose strands of silk have a tendency to get tangled before the spider gets a chance to be lifted into the air. More observations are needed from habitats with trees and shrubs.

How to launch a silkline in the air?
Are the same silk emitting methods used as those described for the start of ballooning? The procedure at the initiation of ballooning and bridging has been the focus of much debate, particularly in behavioural techniques of initiating an airborne silkline. In both ballooning and bridging, a silkline is emitted, which is pulled and lengthened by air currents; it then either grows long enough to lift the spider to become airborne (ballooning) or it gets snagged on a nearby object and the spider walks across using it as a bridge (bridging). The original concept that silk can be spontaneously expelled directly from the spinnerets has been dismissed. It seems impossible because muscles are lacking in the silk glands and the area around the spinnerets. Various techniques which spiders use to produce a line and get it caught by the breeze have been described for an array of spider species. Eberhard (1987) and Jones (1994a, 1994b), amongst others, gave a detailed account of observations, mainly for ballooning spiders, how a strand of silk is created before it is caught by air currents. For ballooning, two principal methods have been reported: one in which a dragline, horizontal or vertical, is used and a breaking point is made. In erigonines starting from erect grass stems for instance, the spider drops a few centimetres and climbs up again, after which it exhibits its tiptoe behaviour and releases silk from the spinnerets. Another strategy has been described, where the spinnerets are spread wide, producing a short bit of thread in between, which is then pulled out further by air friction.

Observations
A holiday in a forest-house in southern Sweden provided an excellent opportunity to test dispersal behaviour in spiders. A series of experiments was done between 16th July and 5th August 2006 during a spell of hot weather (20–30ºC). The house was surrounded by hedgerows, areas of unmown grass and several big trees. The weather was warm and dry with hardly any perceptible wind, occasionally there were short spells of air currents in various directions. The Dolomedes and Misumena were caught while picking red currents (Ribes silvestre) in a row of old shrubs adjacent to the north side of the house.

1. Araniella sp. immature female, 4 mm. This spider was found crawling on one of our sleeves. It appeared to be a specimen eager to disperse so we took her to a stand of dead Anthriscus silvestris (Umbelliferae) flowers. She soon crawled up to the highest point of the stem, made some searching movements, lifting her abdomen now and then. During bursts of air flow she became agitated, rapidly moved her legs and was seen to tap leg IV a few times on the spinneret area. The next moment the spider was moving along a 10 cm bridge spanning the gap to the next flower-head, where she repeatedly shifted her position in various directions. During a short spell of air movement a silkline of about 60 cm appeared. This snagged on the next plant, the spider quickly hauled the line to straighten it and sailed rapidly across at an amazing speed. This was repeated several times till she reached a Ribes shrub.

2. Dolomedes sp., sub-adult, 6 mm. The spider was released on an old horizontal dead branch over a field of unmown grass. During the first experiment the spider remained inert. It was recaptured and released again some days later on the same spot. It started running back and forth a few times, alternating with spells of immobility, when it stretched its forelegs along the surface of the wood. After five minutes it suddenly lifted its abdomen vertically into the air. Twenty seconds later, without any other visible action such as hauling, it walked through the air on a partly invisible line hanging in a loop spanning a distance of almost 6 m and within seconds it had reached a lower branch of an old oak tree. The rapidity of the transfer was puzzling. I did not see the entire stretch of the line, and in retrospect I believe this may have been a case of ballooning rather than bridging.

3. Misumena vatia I, immature, 4 mm. This spider became my dear friend! It exhibited exemplary cooperation. Where Dolomedes was wary and shy, and a rapid runner being disturbed at the slightest commotion (Araniella did not like too much interference either), this little spider did not pay any attention to what I was doing. She allowed me to approach her with my camera at 5 cm and she even let my head and hand-lens approach her at 1 cm! A movable black background was improvised, to make silklines visible.

The spider was placed on the tip of a tall grass-stem, with the nearest object more than a metre away. Within a few minutes a 50 cm long line (clearly visible against the black background) was seen swerving from the spinnerets through a wide angle, showing the versatility of air currents. The spider kept aligning her abdomen with the direction of the line, pivoting around the stem. The length of the produced line stopped growing at 80 cm, too short to snag the nearest object. Several times the spider was seen to reel in the line with the two front leg pairs, after which a new line was initiated. With the front legs the hauled silk was crumpled into a little white knot which either remained on the stem surface or was incorporated into the basal part of a new line. Several times, new lines were set up and reeled in again. Between these activities, during spells of still air, the spider was seen hanging upside down with carapace hanging free, front legs stretched sideways perpendicularly to the body, with legs III embracing the stem, legs IV with knees bent over 90 degrees and tarsal tips touching the stem. Each new line was initiated during a thrust of air movement, by pressing the spinnerets to the substrate, after which the abdomen was visibly “pulled” away, showing a 1 cm long thread between the spinnerets and the substrate. In a quick movement one leg IV disengaged the base of the line, and almost immediately the abdomen was pointed up and a free line shot out. The wind bursts were however weak and the line got caught on my hand lens, the spider moving across and sitting on it. Another attempt brought the spider into my hair. Too much intimacy, time to end the session!

4. Same spider as 3. The next day was a day with more turbulence in the air. The spider was placed on a dead stem about midway between a stone wall and a Ribes shrub, each at a distance of about 1 m from the spider. Immediately legs I and II were spread out in the characteristic way, hanging free and remained so for several minutes. It seems reasonable to interpret this as assessing the new environment and setting its target. During a moment of strong air turbulence the abdomen was pressed against the stem, there was a short rapid movement of legs, a 1 cm long line appeared on the lifted spinneret end of the abdomen and was seen rapidly growing in length. The 20 cm long, very thin line floated in the direction of the wall, but was hauled back in before reaching it. The next flush of air was in the direction of the Ribes and was used to create a new line through the same process as before; this time it grew much longer, but not sufficiently long to reach the Ribes directly. The line became tangled on a stem between the spider and the Ribes and she traversed the bridge. The whole procedure was repeated twice more until, through intermediate objects, the Ribes was reached. The spider settled on the underside of a leaf and the experiment was stopped. 5. Misumena vatia II, a well fed sub-adult female, 6 mm. The spider was placed on a dead Anthriscus stem, 1.20 m from the house; 1 m in the opposite direction was the next dead perennial and another at 1.50 m, the latter adjacent to a concentration of perennials and shrubbery. The observed activities were similar to those of the younger specimen (I). The temperature was lower than the previous days, about 22°C, the wind bursts were much stronger and the predominant direction was towards the house.

Immediately after being released on the top of the stem, she spread the front legs and sat still for a while – she repeated this in various postures and positions (Figure 1). During bursts of wind she became very active and emitted lines just the same way as described for the smaller Misumena; these lines waved in the direction of the house. The lines were slightly thicker and more visible than in the small specimen – some seemed to have been abandoned, others were hauled in and glued on the stem in little balls. Over the next 30 minutes she remained on the spot, alternately stretching legs and moving around. Significantly, only when there arose a burst of airflow in the direction away from the house did she point the abdomen into the air and produced a silkline. After some 20 minutes a crisscross of lines had been created around the point of departure and I saw 3–4 long lines floating around in all directions: one line was attached directly to the spinnerets, others were attached to the substratum or held in one of tarsi I or II.

About half an hour after the beginning of the experiment one of the lines snagged on the nearest dead stem opposite; it was pulled taut and finally she moved heavily and happily along in the direction of her Rubus shrub, just like the one where she had been collected the day before.

Conclusions
1. Producing a free silkline by pressing the tip of the spinnerets on the substrate and pulling out a short strand of silk, has often been described. This behaviour was also observed in Misumena as a start for making a bridge. In Misumena, the strand was seen to be disconnected from the substrate with tarsus IV before the abdomen was pointed upwards to continue the silk flow. In the Araniella and Dolomedes I was unable to see these details; these may very well differ from those in Misumena.

2. Misumena was seen stretching its anterior legs and remaining still between attempts at creating an airborne silkline. The tarsi bear sensory organs, and the action served obviously to identify the physical environment and assess the wind properties. The spider seems to be determined in which direction it wanted to go. Silklines are only propelled during a suitable wind-direction. Araniella and Dolomedes must also have their methods to gather information, but this behaviour differed somewhat from that in Misumena.

Thus, my observations of this summer seem to support a positive answer to the questions posed above: bridging spiders are deliberately aiming at the target they want to reach. Whether these spiders also have the alternative choice to be lifted up in the air to be transported over larger distances remains unanswered. In my opinion, the tested specimens were too heavy for such a way of transport under the given weather conditions and the quality of the silkline. In Dolomedes the bridge was very long; such a long line might easily be mistaken for a ballooning line.

Of course there is nothing new in this. We usually find our spiders exactly where we expect to find them and this means that the spiders are perfectly capable of spotting these places and move into them. Even so, it is exciting to watch them do it! Especially, the speed of expelling silk with the wind is prodigious, even with a low breeze. Indeed, I was surprised by the speed with which some of the tasks were carried out.

I am most grateful to Flip Stoutjesdijk for practical and mental assistance during the experiments, and inspiring tips and ideas concerning microclimatical conditions for ballooning.

Selection of literature
Duffey, E. (1998) Aerial dispersal of spiders. Proceedings 17th European Colloquium Arachnology, Edinburgh. Burnham Beeches, Bucks., UK: 187–192.
Eberhard, W. G. (1987) How spiders initiate airborne lines. J. Arachnology, 15(1): 1–10.
Jones, D. (1994a) How ballooning spiders become airborne. Newsl. Br. arachnol. Soc. 69: 5–6.
Jones, D. (1994b) How ballooning spiders become airborne: a Postscript. Newsl. Br. arachnol. Soc. 70: 4.
Suter, R. B. (1999) An aerial lottery: the physics of ballooning in a chaotic atmosphere. J. Arachnology, 27(1): 281–293. Vanden Borre, J., Bonte, D. & Maelfait, J. (2004) Aëronautisch gedrag (“ballooning”) bij spinnen (Araneae). Nieuwsbr. Belg. arachnol. Ver. 19(1–2): 1–24.

 
Added by John Partridge at 15:40 on Sat 18th Feb 2012.

MISUMENA VATIA (CLERCK) - INFORMATION PLEASE by Dr. G. Oxford

From The Newsletter No. 51 March 1988

Discontinuous variation, other than that related to sex, is relatively uncommon in British spiders. Perhaps the best-known example of this phenomenon is found in Enoplognatha ovata. Another species which apparently has distinct colour varieties, at least in females, is the crab spider Misumena vatia. According to Locket & Millidge (1951, British Spiders I) and Jones (1983, Country Life Guide to Spiders of Britain and Northern Europe) two female forms are found: one has the dorsal surface of the abdomen plain white or yellow (are there two different varieties here?), whereas the other is yellow/ white with two red lateral lines. Roberts (1985, The Spiders of Great Britain and Ireland 1) mentions two pairs of lateral red spots, which may be absent or which can be joined to give the striped form mentioned above. I am interested in just how discontinuous these colour forms are and in their relative frequencies in different populations. I would be very pleased to hear from anyone who has information on either point, or who is willing to collect information for me this spring/ summer. It is worth noting that the red pigment of E. ovata is rapidly lost in alcohol so, if the same thing happens with Misumena, preserved material might be misleading.
 
Added by John Partridge at 16:58 on Wed 4th Jan 2012.

REPLIES TO QUESTION BOX

From The Newsletter No. 20 February 1978

Changes in the colour of the eyes of Thomisid Spiders
In reply to Dr Arthur Lindley's query, Dr W.S. Bristowe writes as follows: "Blackwall, and later 0. Pickard-Cambridge in 1887, both noticed the colour changes in some spiders' eyes. The latter attributed these to slight movements of the spider with corresponding alterations in the reflection of light (1907). Strickland heartily disagreed and said that the changes were brought about 'at the will of the spider' (1906). T.P. Pillai (1908) suggested the posterior tips of the eye cavities could be moved by muscular action to change the field of vision. Whatever it was, it was known to occur in some Salticids and some Thomisids (W.S. Bristowe, The Comity of Spiders Vol. 2. p. 420) and my examination of the phenomenon in living spiders under the microscope convinced me that the conical part of the eye did not move, but that a movement of the retina up and down the cone caused this colour change. This suggested a change in focus but I realised this explanation might be unsatisfactory and provisionally I was tempted to classify the flicker as an enticing movement along with the movements of Salticid spiders' palps when stalking an insect. That was in 1941. Since then others may have had better suggestion to make".

Mr Dick Jones has also written on the same subject as follows: "In the course of a vain attempt to duplicate T.H. Savory's experiment of keeping a Misumena vatia (Clerck) in a transparent container on coloured paper to induce a change of colour my attention was drawn to its anterior median eyes. In a completely random way these two frontal eyes were changing from the normal black glossy appearance to a very pale pink for a fraction of a second and then back to normal again. Occasionally both eyes exhibited this effect together but mostly it occurred to one only and then the other. Although this change happened with great rapidity I thought I observed a corresponding darkening under the chitinous membrane or the head at the side of the eyes whenever they lightened. It appeared as if the eyes were being moved inside the head. I have read in Dr Bristowe's World of Spiders that salticids flicker their eyes when pursuing prey and the objections to this on the grounds of an altered angle of the lighting relative to the observer's line of sight to the eye. However, I took this into account: being a Lecturer in Photography I am all too aware how a tiny change in the angle of a light source can produce varying effects in reflective surfaces, particularly when these are curved but my observations did not indicate this effect to be operating. I have examined salticids for eye movement but so far I have not seen a suspicion of a change, but it was accompanied by an upward movement of the spider's head and I must dismiss my sighting as probably an optical effect. However two specimens of Misumena displayed the same very obvious phenomenon so I set about to photograph it. The larger of the two M. vatia was liberated in my garden where it was seen to catch a number of flies on a large Poppy flower. Several days later I photographed the spider sitting on top of the seed case at 1.5x magnification using electronic flash fixed to the lens. Although the spider is in a slightly different position in each photograph I secured two consecutive frames with similar, if not identical, lighting where in the first shot the right anterior median eye is a fleshy pink, the other a brownish colour (the other eyes being black). The second shot in the same sequence but taken earlier where the lighting is somewhat different (shown by the degree and position of the reflection of light in the eye - known as 'highlight') shows the eyes changed as in my first description. Thus, different angles of light can show the same effect, as photographed, whilst similar angles of light show opposite colours in the two eyes."

Secretary's Note: Those members of our Society whc attended the 6th A.G.M. at Birkbeck College, London on 22nd March 1975 will remember Dr. Michael Land's very interesting lecture on Vision and Behaviour of Spiders when he proved quite conclusively that salticids were able to alter the focus of their eyes by muscular action.
 
Added by John Partridge at 16:55 on Wed 4th Jan 2012.

QUESTION BOX

From The Newsletter No. 19 October 1977

Dr Arthur Lindley, Conservation Officer to Surrey Trust for Nature Conservation sends the following observation and query:
'Earlier this year I led a series of classes for adults, which were intended as an introduction to the taxonomy and ecology of spiders for beginners. On the evening of June 2nd, during one of these classes when we were out in the field sampling the fauna of some rather overgrown heathland, we took an adult female of Misumena vatia (Clerck). Examining it, one member of the class remarked that the spider's eyes appeared to be changing colour. This was corroborated by other members of the class and when I looked at the specimen I observed the following: The two anterior median eyes (and only these two) were switching colour from black to red and back again to black, at an irregular rate, but on average about once every two seconds. There appeared to be no synchronisation between the two eyes, and the switching was visible no matter at what angle one looked; this would seem to rule out an effect due to reflection of light changing as one move to a different view point or re-oriented the specimen. As the switch from one colour to another was very rapid, I imagine the effect was produced by some muscular action behind the spider's eyes. Whether this muscular action was effecting a change in focus of the eyes, or altering some reflective surface behind the retina, or something else, I do not know, and its purpose I could not even guess.

Has this phenomenon been recorded before for Thomisid spiders and has anyone made any investigation of its causes?'
 
Added by John Partridge at 16:46 on Wed 4th Jan 2012. Return to Summary for Misumena vatia