SUMMARY
Spiders are one of the most widespread arthropods which are widely known for their web building activities. Their presence ranges from houses to fields and they can build their web anywhere. They have special structures called spinnerets to build the web; meanwhile, legs help them weave the web. Spiders are arthropods that have 4 pairs of legs and mostly it is believed that they have evolved extra pairs of legs as it is known that they can survive easily even after losing few legs. It is a frequent instance for spiders to lose legs through autotomy when they remove their own legs to escape any predator. Autotomy helps them get away from the predator quickly, but the loss of legs have certain costs that include altered web building behavior and thus, web parameters.
The aim of this study was to assess the effect of autotomy on web building behaviour so that we can measure altered web parameters in order to determine how autotomy affects spiders in the wild. To find that out, spiders were divided into three groups; control group, forelegs removed group, and hind legs removed group. Spiders were captured from Farooka and then kept in specially designed wooden boxes covered with PVC sheets. The spiders in the control group had intact legs while in the forelegs removal group, the first two pairs of legs (I & II) were removed. While in the hind legs removed group the last two pairs of legs (III & IV) were removed. Spiders were given two house flies daily as feed to keep them alive and also observe their prey capturing behaviour and how legs loss affects it. The legs of the spiders were removed from femur-trochanter joint Observations were made every morning and pictures of the webs were taken. The web parameters (Number of spirals, mesh height, number of radii, web diameter, radius, capture area, and anchoring thread length) were noted and compared.
Results showed that the removal of forelegs had no significant impact on the web parameters of the orb-web spider whilst hind legs removal caused a considerable change in the web parameters altering number of spirals, number of radii, and anchoring thread length. Results of this study has provided data to conduct in-depth future researches to find study detailed impacts of loss of legs on web architecture of spiders.
INTRODUCTION
Spiders are among the oldest, most omnipresent and numerous predators in both agricultural and natural ecosystems. Many spiders are specialized web spiders, whereas others hunt their victims. Their webs serve the purpose of catching the prey by trapping it in the intricately built webs. Insects constitute the major source of prey for spiders, but certain other arthropods are often consumed as well. Thus spiders are regarded high in value for pest control (Foelix, 1982).
Spiders are predators that have developed a great variety of different ways to capture prey. All spiders produce silk and several species use this ability to construct webs as catching devices. Among the various kinds of web-building spiders, orb weavers have specialized to build webs that catch airborne prey (Craig, 1986).
Only web spiders use their ability to produce silk for the construction of webs. They mostly use fourth leg to build the web using silk ejected from silk glands. The well-known orb-shaped web is one of the many kinds of webs built by different spider families (Herberstein, 2000). There are significant variation within species and it has effect on prey capture ability. Webs of different size, inclination and mesh height will capture different types and sizes of prey at different rates. (Uetz et al., 1978). The orb web is certainly the best known of all webs. Essentially it is made up of three components which are radial threads, spiral threads, and frame threads. Web building is an innate behaviour of spiders yet experience and learning also plays role in web-building (Chacon et al., 1980).
Many spiders lose legs when they come across predators. (Roth, 1984) Almost 10% of all orb web spiders lose one or more legs during their life with serious consequences for their fitness (Vollrath, 1998). Loss of an appendage can impair foraging abilities, locomotor performance, competitive abilities, and mating. With the loss of one or more legs, female orb-weaving spiders can be penalized twice: firstly, because the legs are necessary for web construction and secondly, the legs are essential for the control of the prey after its interception by the web. In orb-weaving spiders, the use of the eight legs is of extreme importance during web construction. Indeed, a full set of leg is utilised during the installation of various types of threads (Pasquet et al., 2011)
After autotomy, juvenile individuals may regenerate the lost appendage during a subsequent molt. It is known however that a regenerated leg, which is generally shorter than a normal one, generates structural modifications of the web (Witt et al. 1968). For orb-weaving spiders during their adult life, autotomy could first result in the modification of construction behaviours, inducing possible alterations of the web properties, and thus decreased prey interception efficiency. Secondly, handicapped spiders could be less efficient in locomotor activity to capture the prey (Pasquet et al., 2011).
The effect of leg autotomy differs with the habitat of the spider species as well. Their foraging ability and walking speed varies after leg loss depending on the type of habitat in which they live but it is generally observed that the walking speed of the spiders become less after losing their legs. (Amaya, 2001).
Leg autotomy occurs in spiders when a leg was pulled or injured. It occurs consistently at the level of the coxa-trochanter joint near the base’ of the leg. A special mechanism provides for minimization of bleeding at the site of leg detachment, and spiders can withstand the loss of one or two pair of legs (Camazine, 1983).
So keeping in view, the importance of legs for web building our study aimed at studying how loss of legs can impair web characteristics and web building in spiders.
OBJECTIVES
- This study aims at assessing the effect of legs loss on architecture of web built by spiders.
- Another objective of this study is to assess the altered web characteristics due to loss of legs.
REVIEW OF LITERATURE
Under challenging circumstances, many animals, both invertebrates and vertebrates will sacrifice a body part, frequently a leg. According to a review (Fleming et al., 2007), members of three vertebrate classes, as well as five phyla and 14 classes of invertebrates, are known to engage in this behaviour. Fleming in 2007 defined the concept of Autotomy according to which autotomy is the deliberate, anxiously mediated defensive action of self-amputation of a limb or other appendage. Autotomy is the ability to lose a grasped or blocked appendage by reflex, and in some species, the lost limb can then regenerate. Lizards and spiders are some known examples (Maiorana, 1977). .
Autotomy can happen in response to a variety of unfavorable yet external circumstances, such as fleeing from a predator or emerging from a molt, engaging in intra or interspecific combat, contracting an infection or being envenomed, or reacting to shocks. However, the intensity of autotomy depends not only on external factors but also on the specie kind. (Guffey, 1999; Fleming et al., 2007).
When an animal is either being grabbed by a predator (such as the salamander or spider is attempting to divert a predator, limb autotomy frequently occurs. Therefore, an increase in individual survival is the most visible fitness gain an individual receives from autotomizing one of its appendages. When assaulted by a scorpion, for instance, spiders of the genus Filistata will autotomize one or more of their legs (Formanowicz, 1990). This motion diverts the predator and gives the spider a chance to get away. Even if the spider is successful, autotomy may still have long-term effects that reduce the organism’s overall fitness compared to those still intact. Research says that though Autotomy helps the invertebrate to get an escape, but till the time it regenerates it lost part, the life is not simple. However, for those invertebrates, if the number of legs is more, for instance, eight, it will easily carry on with activities but a little slow (Fleming et al., 2007).
All spider species are supposedly capable of growing new legs (Brown et al., 1995; Foelix, 1982). In other species, the legs of captured or wounded animals are even appendotomized or detached at specific joints (Wood, 1926; Bauer, 1972; Roth, 1984). Spiders shed an appendage by using Autotomy or autotilly. By rotating the articulation or by tearing with the help of chelicerae and other legs, the animal itself cuts the leg from the body in autotilly. In Autotomy, the joints are separated by an internal mechanism without the use of external force. Whether an animal cuts off a leg by autotilly or Autotomy appears to depend on the species (Roth, 1984).
It has also been found that Autotomy reduces spider fitness by adversely affecting their capacity and success at foraging. Losing a limb can affect a spider’s ability to move, as seen by the much slower running speeds of spiders with fewer than eight legs (Amaya et al., 2001; Apontes et al., 2005; Brown et al., 2012). Although studies testing foraging performance in spiders with autonomies have shown mixed findings, limb loss may also influence a spider’s capacity to acquire prey and adversely impact the web architecture. While Brueseke et al. (2001) discovered that autotomized Pardosa milvina consumed smaller crickets than their intact counterparts, Amaya et al. (2001) found no difference in the number of attacks required to capture prey items between intact and autotomized spiders of two species. When examined on a diverse, natural substrate, scientists discovered that Schizocosa ocreata ones with autotomized legs had lower prey catch rates, and their web architecture plus the ability to make web gets poor (Uetz et al., 2008).
More than half of the 40,000 spider species make webs that serve as a trap, composed of a silky structure that can catch and hold prey (Foelix, 2011). These structures come in a wide variety, but the geometrical webs have predictable structural patterns. Although variations in the establishment of the attachment points, frame, and radial threads, which involve modifications of the behavioral sequences such as thread addition and removal, are known to occur in these webs. The sticky and auxiliary spirals, composed of a series of silk lines between two radii, result from repetitive behaviors and with the help of legs (Zschokke, 1996).
The spider web is something worth noticing. It has been argued that if a spider loses a pair of the leg, it becomes difficult for it to weave webs, just as getting food and movement is difficult for them. Orb webs have stunning architecture, especially with their geometric uniformity. The following is a description of how such webs are made: First, the spider attaches silk threads to the supports that make up the framework for the web. Next, the spider weaves the web. The spider builds the radii first, followed by an auxiliary spiral that is formed from the center out. The spider then places a sticky spiral (capturing thread) by traveling towards the center of the web from the edges while utilizing the auxiliary spiral as a guide (Foelix, 2011). The existence of radii surrounding the hub and the sticky spiral attached to these radii characterize the geometry of the orb web. The orb web design is known to change depending on external or internal factors. Studies conducted show that morphological handicap (missing or a shortened limb) impacts the weaving process of web, and in most of the cases the spiders are not able to weave (Punzo, 1997). Web features are also a direct reflection of spider behavior and can change at the intraspecific and intra-individual levels (Heiling et al, 2000).
The position of each string releases the sticky spiral that is used to weave webs depending on information perceived by the movements of the first pair of legs (L1) (Vollrath, 1985). The orb-web structure anomalies are linked with abnormal leg positions (Eberhard WG, 1990). The first pair of a spider’s legs (legs I) are the most anterior, and the fourth pair (legs IV) is the most posterior. Each set of the spider’s walking legs has a different purpose when it attacks its victim, but legs I and IV are particularly crucial. To attack prey, wolf spiders often make short leaps. Legs I are elevated in a high arc first, and then legs II are raised similarly. The spider will then use legs IV to propel itself forward and slant upward as it leaps toward the prey object. The spider’s front set of walking legs (I and II) make first contact with the prey, and its back set of walking legs (III and IV) are subsequently used to move (Parry, 1957).
The usage of the fourth legs is crucial while creating a web in orb-weaving spiders. Indeed, while installing different varieties of threads, a full complement of legs is used (Foelix, 2010). Juvenile individuals who have undergone autotomy may recover the missing appendage during a subsequent molt. However, it is understood that a regenerated leg, which is often shorter than a normal one, results in structural changes to the web. Regeneration is impossible when autotomy develops in adults who are no longer able to shed their skin. When orb-weaving spiders reach adulthood, autotomy may first change their construction behaviors, which may then modify the web’s characteristics and reduce the effectiveness of their prey interception. Second, spiders with disabilities may be less effective in catching prey through locomotor activity. Since males do not produce webs as adults, autotomy in these situations may impair female fitness, particularly by limiting the accumulation of reserves required for egg development (Wrinn et al., 2007).
The disadvantage for adult orb-weaving spiders that are unable to regenerate damaged limbs as adults may be threefold when compared to earlier research focusing on spiders that do not spin webs (Amaya et al., 2001; Brueseke et al., 2001; Uetz et al., 2008). Though spiders, in case of a problematic situation, lose their leg through the process of autotomy, later on, they soon realize that movement, taking food, and weaving web are now difficult because of a missing leg (Rypstra et al., 2007).
MATERIALS AND METHODS
Spider Collection:
Spiders Neoscona theisi were collected from field areas in Sargodha. The areas were selected randomly on the basis of presence of fields. Areas that were selected to collect spiders from are Farooka (31.88O N, 72.41 O E). Spiders were collected during normal weather conditions when it is neither rainy nor windy. The sampling was completed in the duration of four months from June to September 2022.
Capturing Spiders:
To capture an orb-web spider from its web, a small jar which was (4’ x’6’’) was placed beneath the web. Then the web was slightly tapped from to drop it into the jar and cover was placed from other side of the web. Before transferring live spiders to the wooden arena designed for their captivity, many twigs, leaves, and wet cotton swab was placed into the jars. The small twigs and leaves were added to give them the sense of a natural environment and cotton swabs provided the necessary humidity. For each samples, a separate jar was used so that they do not eat each other as spiders are known for cannibalism. Spider samples were then divided into three groups; Control Group, Group I (Two pairs of forelegs removed), and Group II (Two pairs of hind legs removed). The samples were carefully observes for assuring the presence of all four pair of legs as first two and last two pairs were removed to perform the experiment and find out the results.
Enclosure to Keep the Spiders:
Wooden frames of 2/2 feet were used to keep the spiders alive and study the web-building of the spiders and the behaviour related to it. To keep the web safe and prevent the spiders from escaping, the frame was covered with thin, slightly transparent, and rather flexible PVC sheet from both sides. On the inside, there were hooks to attach a thread to provide anchoring support to the spider to build the web by attaching the anchoring thread of the web. The spiders were kept hungry for three days before introducing them into the frames so that the strongest spider survives and is used in the experiment.
As frames were kept in the same place yet they were separated from each other by thin PVC sheets. In order to prevent silk threads from getting attached to the sheets, the sheet was smeared with Vaseline from both sides. The sheet could be removed easily from both sides to introduce spider and provide feed to the spider. Additionally, wet cotton swabs were placed in the corners of the wooden box to provide the required humidity that ranges from 65-70%. Then the samples were carefully transferred into the wooden frames. All wooden arenas were kept in a place that does not receive direct sunlight and the temperature is 27±3 with the light and dark cycle of 11:13 hours.
Feeding the Spiders:
Spiders were given two live houseflies (Musca domestica) and the feed was kept constant throughout the experiment. The flies were captured using honey jars by quickly closing the lid as soon as they entered the jar. The live and buzzing prey acted as a bait to lure the spider to build the web and trap that prey. Then they were transferred to the wooden boxes by removing PVC sheet from one side and tapping the jar onto the edge.
Cutting the limbs:
As we have to study the effect of legs loss thus the spiders must be handicapped. They have inbuilt mechanism of autotomy so the loss of legs will be induced in them. Their legs will be stretched from coxa-trochanter joint using a bicep so that they self-amputate their legs. But if they do not then the leg will be cut from coxa-trochanter joint.
Grouping of Spiders:
Spiders were subdivided into three groups in order to study effect of legs loss for two subsequent pairs. Thus one will be control group with intact legs. While there were two test groups with legs removed.
In group I, first two pairs (I & II) of legs were removed. In group II, last two pairs of legs were removed. The two pairs were removed to study the significant difference as spider can easily survive with the loss of one pair.
Web Parameters and Imaging:
Pictures of webs were taken with Oppo F19 against a dark background and every other day web parameters were noted after observing the web building at each observation. The images were takes at the dawn using Oppo F19 android cellphone. At every observation, the parameters recorded were number of spirals, number of radii, and diameter of the web (vertical and horizontal both), radius of the web, mesh height, anchoring thread length, and capture area. As the web of the spider is elliptical that is why it was calculated using the “Ellipse formula”. The total surface area of the web of the spider is called as capture area. (Herberstein and Tso, 2000).
Capture Area= (dv/2) (dh/2)π
Where dv stands for vertical diameter and dh for horizontal diameter.
When every observation was done and parameters were recorded, the previous web was destroyed and spiders were kept in the wooden box again to let them build another web. All the conditions were maintained throughout and food supply was given constantly. The prey entanglements and capturing was also observed for every group at each observation.
Statistical Analysis:
To compare the effects of legs loss on the web building and web parameters of test groups with controls, a one-way ANOVA was applied followed by Tukey’s test. To compare the effect of legs removal of both groups with control group, two sample t-test was used. Both of these tests were applied using GraphPad Prism 8.0.1.
RESULTS
The results of this study are:
Web building and web parameters:
First of all, observations of controlled groups were made that had all normal parameters and web-building. It showed no degree of difference as all the legs were intact and conditions provided were normal, nearly similar to the ones in the wild. The results of the observations varied for the treated groups with spider samples. Their legs were removed and they showed different web-building and web parameters from the controlled group. The results of group I with forelegs removed did not show much variation from the controlled group. The results varied very little from normal and they showed not much difference in building the web.
When the webs of the first group were observed, only the number of spirals slightly varied and that too was negligible. This study did not show significant importance of forelegs in the building of the web except for one parameter. The parameter that was altered due to the loss of forelegs was the length of anchoring thread that is considerably greater from the control group. The results through comparison of control group and group I through T-test showed significant difference for number of spirals (P-Value=0.0055) while number of radii showed slightly significant difference (P-Value=0.0065). The anchoring thread length was also significant (P-Value=0.0038).
When the group II was observed, the results were significant. This group has spiders with two pairs of hind legs removed. The results showed much impact on the web-architecture of the spider as a few parameters were significantly altered. These parameters that varied considerably are the number of spirals, the number of radii, and anchoring thread length. The rest of the parameters did not show much variation. The results through comparison of control group and group II through T-test showed highly significant difference for number of spirals (P-Value=0.0409) while number of radii also showed significant difference (P-Value=0.00260). The anchoring thread length was also significant (P-Value=<0.0001)
The prey capture was observed in all three groups. All spiders were able to capture spiders in their webs, but the observations for prey handling was a little different for the group I with forelegs removed. The spiders in group I with missing forelegs were observed to be slow to seize the fly, and 20% webs, one fly was found to be just trapped in the web but not eaten. It was confirmed through continuous observation that the group I spiders were slow in seizing their prey.
Table No 1: Comparison of web building between Forelegs Removal group (Group I) and Hind Legs Removal (Group II) using ANOVA
|
Sr. No |
Parameters | Treatments | Mean±SE | Df | P-Value | F-Value |
| 1 | No. Of Spirals | Control Group | 28.50±1.241 | 2.27 | 0.0140 | 5.022 |
| Group I | 26.90±1.206 | |||||
| Group II | 23.40±1.035 | |||||
| 2 | No. of Radii | Control Group | 26.70±1.325
|
2.27
|
0.0122
|
5.214
|
| Group I | 25.30±1.174 | |||||
| Group II | 21.40±1.097 | |||||
| 3 | Mesh Height | Control Group | 3.165±0.065 | 2.27 | 0.4337
|
0.8618
|
| Group I | 3.258±068 | |||||
| Group II | 3.141±0.065 | |||||
| 4 | Diameter | Control Group | 19.69±0.389 | 2.27 | 0.3948
|
0.9622
|
| Group I | 19.36±0.370 | |||||
| Group II | 18.96±0.57 | |||||
| 5 | Radius | Control Group | 9.880±0.183 | 2.27 | 0.3093
|
1.226
|
| Group I | 9.730±0.184 | |||||
| Group II | 9.480±0.178 | |||||
| 6 | Capture Area | Control Group | 314.1±
12.73
|
2.27 | 0.7587
|
0.2790
|
| Group I | 310.4±
12.64
|
|||||
| Group II | 301.5±
11.44
|
|||||
| 7 | Anchoring Thread Length | Control Group | 39.05±
0.8083
|
2.27 | <0.0001
|
20.22
|
| Group I | 42.20±
0.6864
|
|||||
| Group II | 35.13±
0.8583
|
Table No 2: Comparison of web building between control group and Forelegs Removal (Group I)
| Sr. No | Parameters | Treatments | Mean±SE | Df | P-Value | T-Value |
| 1 | No. Of Spirals | Control Group | 28.50±
1.241 |
18 | 0.3673
|
0.924 |
| Group I | 26.90±
1.206 |
|||||
| 2 | No. of Radii | Control Group | 26.70±
1.325 |
18 | 0.4395
|
0.790
|
| Group I | 25.30±
1.174 |
|||||
| 3 | Mesh Height | Control Group | 3.165±
0.06522
|
18 | 0.3385
|
0.893 |
| Group I | 3.258±
0.06850
|
|||||
| 4 | Diameter | Control Group | 19.69±
0.3894
|
18 | 0.5467
|
0.614 |
| Group I | 19.36±
0.3700
|
|||||
| 5 | Radius | Control Group | 9.880±
0.1837
|
18 | 0.5720
|
0.575 |
| Group I | 9.730±
0.1849
|
|||||
| 6 | Capture Area | Control Group | 314.1±
12.73
|
18 | 0.8379
|
0.207 |
| Group I | 310.4±
12.64
|
|||||
| 7 | Anchoring Thread Length | Control Group | 39.05±
0.8083
|
18 | 0.0082
|
2.971 |
| Group I | 42.20±
0.6864
|
Table No 3: Comparison of web building between control group and Hind Legs Removal (Group II)
| Sr. No | Parameters | Treatments | Mean±SE | Df | P-Value | T-Value |
| 1 | No. Of Spirals | Control Group | 28.50±
1.241 |
18 | 0.0055
|
3.157 |
| Group II | 23.40± 1.035
|
|||||
| 2 | No. of Radii | Control Group | 26.70±
1.325
|
18 | 0.0065
|
3.080 |
| Group II | 21.40±
1.097
|
|||||
| 3 | Mesh Height | Control
Group |
3.165±
0.0652
|
18 | 0.7987
|
0.258
|
| Group II | 3.141±
0.0659
|
|||||
| 4 | Diameter | Control
Group |
19.69±
0.3894
|
18 | 0.1844
|
1.380 |
| Group II | 18.96±
0.3578
|
|||||
| 5 | Radius | Control
Group |
9.880±
0.183
|
18 | 0.1362
|
1.560 |
| Group II | 9.480±
0.178
|
|||||
| 6 | Capture Area | Control
Group |
314.1±
12.73
|
18 | 0.4701
|
0.737 |
| Group II | 301.5±
11.44
|
|||||
| 7 | Anchoring Thread Length | Control
Group |
39.05±
0.8083
|
18 | 0.0038
|
3.325 |
| Group II | 35.13±
0.8583
|
Table No 4: Comparison of web building between Forelegs Removal group (Group I) and Hind Legs Removal (Group II)
| Sr. No | Parameters | Treatments | Mean±SE | Df | P-Value | T-Value |
| 1 | No. Of Spirals | Group I | 26.90±
1.206
|
18 | 0.0409
|
2.202 |
| Group II | 23.40±
1.035
|
|||||
| 2 | No. of Radii | Group I | 25.30±
1.174
|
18 | 0.0260
|
2.426 |
| Group II | 21.40±
1.097
|
|||||
| 3 | Mesh Height | Group I | 3.258±
0.068
|
18 | 0.2343
|
1.231 |
| Group II | 3.141±0.065
|
|||||
| 4 | Diameter | Group I | 19.36
±0.370
|
18 | 0.4472
|
0.777 |
| Group II | 18.96± 0.3578
|
|||||
| 5 | Radius | Group I | 9.730±
0.184 |
18 | 0.3441
|
0.971 |
| Group II | 9.480±
0.1789
|
|||||
| 6 | Capture Area | Group I | 310.4± 12.64
|
18 | 0.6079
|
0.522 |
| Group II | 301.5±11.44
|
|||||
| 7 | Anchoring Thread Length | Group I | 42.20±0.686 | 18 | <0.0001
|
6.433 |
| Group II | 35.13±
0.8583
|
DISCUSSION
In our study, the effects of the loss of legs by removal of two pairs of forelegs and two pairs of hind legs on the web architecture of an orb-web spider Neoscona theisi was studied. It is an orb-weaving spider that uses all of its eight legs in constructing the web. While installing various types of silk, they use the full set of legs for that purpose and make a framework of the web (Foelix, 1996). Another aspect of the legs loss that we observed was prey capture, which did not vary significantly with the loss of legs except for negligible number of webs. It is because left forelegs (I & II) have a considerable role in touching and exploring the prey (Govind, 1988, Ades, 2002).
Leg autotomy is a good strategy for escaping from predators in several animals. In spiders, autotomy is common (5–40% of spiders may have missing legs) and it reduces their speeds and can affect the ability to find mate, food, mates etc (Gerald, 2017).
Our results showed that the removal of group I has not much effect on the web characteristics of the spider. There was some distance between the turns of the spiral for a few webs but the results were not impacted by that much difference. This result is also supported by the spare-leg hypothesis (Guffey, 1999). Our results were also in accordance with the study conducted by Alain et Al., 2011. Spiders can easily lose two legs and still survive in the wild with web parameters almost remaining unaffected (Alain et Al., 2011).
Another study conducted by Vollrath (1987) studied that spiders use all of its legs present on one side of the body to measure the distance between subsequent spirals. The role of forelegs is only that they find the point where the capture spiral is to be placed and that is why the web parameters were not much affected with the removal of forelegs. So, when the first two pairs of the legs are removed there is no affect on web parameters like number of spirals and mesh height.
The prey capture though was slightly affected by the removal of forelegs as it is proved that legs I and II are important in chasing the prey. When it comes to sensing and capturing the prey leg I have a significant role in doing that. Though spiders can effectively capture the prey despite removal of legs because the rest of the legs are capable of performing all functions to survive according to the “Spare-leg hypothesis”, I & II have shown to more effectively capture the prey according to the study of Ades (2002).
Another study also confirms that spiders with regenerated short forelegs did not differ greatly in web-building behavior from normal spiders and the webs had functional parameters (Krink et al., 1999). In Araneus. diadematus, like most other orb spiders that have all their legs, the two pairs of front legs detect the presence of threads and measure distances while the spinneret lays and affixes the silk assisted by the fourth pair of legs with the third pair holding onto the supporting threads (Vollrath and Krink, 2020).
The second group which had spiders with hind legs removed showed significant differences in web parameters. According to our results the web parameters that differed from control group were number of spirals, number of radii, and anchoring thread length. The study of Vollarth (1987) supports these results as they worked with spiders who had grown shortened hind legs after autonomy. According to that study, spirals are fixed by legs III & IV. It measures the placement of the next spiral from the capture spiral and so on, thus the difference in the number of spirals (Vollrath, 1987).
CONCLUSION
This study concludes that forelegs have no significant impact on web building and without them spiders can build a normal web. The removal of hind legs cause significant changes in web parameters particularly number of spirals as leg III & IV are important in the placement of spirals. Still, this topic needs further elaborate studies both in the wild and in laboratory because web building behavior of spiders is subject to a lot of factors.
References
- Amaya, C. C., Klawinski, P. D., … and Formanowicz, D. R. (2001). The effects of leg autotomy on running speed and foraging ability in two species of wolf spider (Lycosidae). Am Midl Nat., 145(1), 201-205.
- Ades, C., and Ramires, E. N. (2002). Asymmetry of leg use during prey handling in the spider Scytodes globula (Scytodidae). J. Insect Biol., 15(4): 563-570.
- Apontes P., and Brown CA (2005) Between-sex variation in running speed and a potential cost of leg autotomy in the wolf spider Pirata sedentarius. Am Midl Nat., 154:115–125
- Brown, R.M., Taylor, D.H., … and Gist, D.H. (1995). Effect of caudal Autotomy on locomotor performance of wall lizards (Podarcismuralis). J. Herpetol., 29: 98–105
- Eberhard, W. G. (1989). Effects of orb web orientation and spider size on prey retention. Bull. Br. Arachnol. Soc., 8(2): 45-48.
- Eberhard WG (1990) Function and phylogeny of spider webs. Annual Review Ecol Syst., 21: 341–372
- Fleming, P. A., Muller, D., … and Bateman, P. W. (2007). Leave it all behind: a taxonomic perspective of Autotomy in invertebrates. Biol. Rev., 82: 481-510
- Foelix, R. F. (1982). Biology of spiders. Harvard University Press.
- Foelix, R. (2010). Biology of Spiders. Oxford Univ. Press, New York, USA.
- Gerald, G. W., Thompson, M. M., Levine, T. D., & Wrinn, K. M. (2017). Interactive effects of leg autotomy and incline on locomotor performance and kinematics of the cellar spider, Pholcus manueli. Ecol. Evol., 7(17), 6729-6735.
- Guffey, C. (1999). Costs associated with leg autotomy in the harvestmen Leiobunum nigripes and Leiobunum vittatum (Arachnida: Opiliones). Can. J. Zool., 77(5), 824- 830.
- Heiling A. M., and Herberstein M. E., … and Spitzer G. (1998) Calculation of capture thread length in orb webs: evaluation of new formulae. Ann Entomol Soc Am. 91: 135–138
- Herberstein M. E., and Heiling A. M. (1998) Does mesh height influence prey length in orb webs spiders (Araneae). Eur J. Entomol., 95 :367–371
- Herberstein, M. E., Craig, C. L., Coddington, J. A., … and Elgar, M. A. (2000). The functional significance of silk decorations of orb-web spiders: a critical review of the empirical evidence. Biol. Rev., 75(4): 649-669.
- Heiling A.M., and Herberstein M.E., (2000). The importance of being larger: intraspecific competition for prime websites in orb-web spiders (Araneae, Araneidae). Anim. Behav., 136: 669–677
- Krink, T., and Vollrath, F. (1999). A virtual robot to model the use of regenerated legs in a web-building spider. Anim. Behave., 57(1): 223-232.
- Maiorana, V. C. (1977). Tail autotomy, functional conflicts, and their resolution by a salamander. Nat., 265: 533-535.
- Parry, D. A. (1957). Spider leg-muscles and the autotomy mechanism. Journal of Cell Sci., 3(43): 331-340.
- Pasquet, A., Anotaux, M., … and Leborgne, R. (2011). Loss of legs: is it or not a handicap for an orb-weaving spider?. Naturwissenschaften, 98(7): 557-564.
- Punzo, F. 1997. Leg autotomy and avoidance behavior in response to a predator in the wolf spider, Schizocosa avida (Araneae, Lycosidae). Journal of Arachn., 25: 202-204
- Roth, V. D., and Roth, B. M. (1984). A review of appendotomy in spiders and other arachnids. Bull. Br. Arachnol. Soc., 6(4): 137-146.
- Schneider, J. M., and Vollrath, F. (1998). The effect of prey type on the geometry of the capture web of Araneus diadematus. Sci. Nat., 85(8): 391- 394.
- Uetz, G. W., and Hartsock, S. P. (1987). Prey selection in an orb-weaving spider: Micrathena gracilis (Araneae: Araneidae). Psyche., 94(1-2): 103-116.
- Venner, S., Casas, J. (2005). Spider webs designed for rare but life-saving catches. Pro R Soc B., 272:1587–1592
- Venner, S., Thevenard, L., Pasquet, A., … and Leborgne, R. (2001). Estimation of the web’s capture thread length in the orb-weaving spiders: determination of the most efficient formula. Ann Entomol Soc Am. 94: 490–496
- Vollrath, F. (1987). Altered geometry of webs in spiders with regenerated legs. Nat., 328(6127), 247-248.
- Vollrath, F., Downes M, … and Krachkov, S. (1997) Design variability in web geometry of an orb-weaving spider. Physiol Behav., 62: 735–743
- Vollrath, F.1992. Analysis and interpretation of orb spider exploration and web- building behavior. Adv. Stud Behav., 21: 147–199.
- Vollrath, F., & Krink, T. (2020). Spider webs inspiring soft robotics. J. R. Soc. Interface, 17(172), 20200569.
- Wrinn, K. M. &Uetz, G. W. 2007: Impacts of leg loss and regeneration on body condition, growth, and development time in the wolf spider Schizocosa ocreata. Can. J. Zool. 85: 823—831.
- Wrinn KM, Uetz GW (2008) Effects of Autotomy and regeneration on detection and capture of prey in a generalist predator. Behav Ecol., 19:1282–1288
- Zar, J.H. (1984). Biostatistical analysis. 2nd ed. Prentice-Hall, Inc
- Zschokke, S. (1993). The influence of the auxiliary spiral on the capture spiral in Araneusdiadematus (Araneidae). Bull. Br. Arachnol. Soc., 9: 169–173.