SPIDERS DIVERSITY by Dr. Pankaj w. Chaudhari
Overview
Its a chapter of my Book on diversity of Spiders from Yavatmal and adjecent area.
SPIDERS
INTRODUCTION:-
Liveliness is the exclusive character of Earth, with a vast biodiversity but, the entire flora and fauna is not yet recognized and still awaiting for its identification in different ecosystems. Arthropods are the most diverse group amongst the animal kingdom and class Arachnida rank seventh in total species diversity with all other groups of organisms. Spiders are abundant generalist predators in terrestrial habitats and they are also an important source of food for other animals and forms a valuable part of ecosystem. Order Araneae or spiders belong to class; Arachnida of phylum Arthropod. The current world list of spiders includes 45,776 species under 3974 genera distributed over 114 families (WSC, 2016). In India they are represented by 1686 species belonging to 438 genera of 61 families (WSC, 2015; Keswaniet al., 2012). Keswaniet al., (2012) listed 91species of Mygalomorphae under 28 genera belonging 8 Families. Present list includes a total of 111 species of Mygalomorphae distributed over 32 genera under eight families from India. The name Arachnida was given by Lamarck in 1815 when he separated Scorpions, Spiders and Mites from the order Aptera of the Linnean Insecta. (Savory, 1928)
Spiders (Order Araneae) are air breathing arthropods evolved in Devonian era about 386 million years ago. True spiders have been found in Carboniferous rocks from 318- 299 million years ago. The main groups of modern spiders Mygalomorphae and Araneomorphae originally emerge in the Triassic period before 200 million years ago. Spiders like arachnids with silk producing spigots evolved during the Devonian period but these animals truly lacked spinnerets. Spiders differ from other arthropods in various aspects but the main character of spider is to produce the web.
Spiders secrets the fluid to produce silk through spinnerets, which hardens on contact with air. Six types of silk glands are located within the abdomen that has been modified in spinnerets that extrude silk.
Generally spider species are divided into two suborders: Mesothelae (segmented spiders) and Opisthothelae (includes all other spiders). Later one is again divided into two infraorders: Mygalomorphae (ancient spiders such as tarantulas, trapdoor and funnel web spiders) and Araneomorphae (modern spiders include the vast majority of spiders) (Coddington, 2005; WSC, 2015). The segmented spiders are easily distinguished by groove on the top of the abdomen, evidence of spider’s common ancestry with scorpions (Culin et al., 2014).
Most spiders are cannibalistic in nature they feed upon other species of spiders; few species of spiders that construct web exist together in large colonies and shows social behavior. The most social species probably from genus Stegodyphus which forms colonies up to fifty thousand individuals. (Tikader and Biswas, 1981)
All spiders try to protect themselves by biting, especially if they are unable to run away. Some Tarantulas have different type of defense, with a patch of urticating on their abdomen, these ultra fine hairs causes irritation and sometime even allergic reaction during the attack. Some other species of spiders for example, the golden wheeling spiders of the desert Namibia escapes Tarantula hawks by flipping on to its side and cart wheeling away.
The biodiversity of invertebrate species on agricultural land is very important in terms of pest control and conservation. Spiders are dominant predator found in Arthropods communities (Gertssch, 1979).
Spiders are important but in general poorly studied arthropods due to unawareness, lack of knowledge, fear and general dislike towards them. The broadly spread concept that spiders are toxic and dangerous, may be the one of reason to stay away from them. All spiders are not venomous only a small number of species such as Black Widow spider, Recluse spider or Red Back spiders bite is harmful for human beings, and sometime they may cause allergic reactions. Venom produced by spiders is poisonous to their common pray like insects, mites and other small Arthropods; venom is inserted to pray through the fangs to immobilize them. Spiders only use their venom to immobilize their prey and hence they act as natural pest controller, so the study of diversity and variety of spiders in agro ecosystem is useful for determination of the benefits of agricultural practices for conservation of spiders, important for pest control (Eyre et al., 1989). Spiders are wide spread in agro ecosystems making up to 20-80% of predatory fauna (Legotay, 1980; Zhang, 1992).
Citrus canker is a disease, affecting citrus trees, caused by the bacterium Xanthomonas axonopodis, infection causes lesions on the leaves, stem and fruits, these bacteria are carried by citrus leaf miner larvae (Phyllocnistiscitrella).
To control effects of pests various pesticides are regularly been used by farmers, but these pesticides are having various adverse effects on non target fauna, sometimes these pesticides are harmful to human beings also, therefore more emphasis should be given on bio-pesticides, spiders plays major role in controlling population of insect pests.
There are still major gaps in our knowledge of diversity of spiders in many areas within varied ecosystems of India. Here the attempt was made to find out the comparative diversity of spiders from forest area around Upper Wardha Dam as well as citrus fields in nearby area. The data will remain helpful to analyze the spider’s fauna in both the ecosystems, as well as their role in citrus fields as integrated pest management.
1.1Evolution of spiders
The evolution of spiders has been going on for at least 380 million years, since the first true spiders (thin waisted arachnids) evolved from crab like chelicerate ancestors. The oldest known ground arthropods are Trigonotarbids, members of an extinct order of spider like arachnids. (Garwood, 2011) Trigonotarbids share many external characteristics with spiders, including a terrestrial lifestyle, respiration through book lungs, and walked on eight legs, with a pair of leg like pedipalps near the mouth and mouth parts. Influence still stays open as they possessed the ability to create silk. This had been an accepted consideration for quite some time, until an unpublished fossil was described with distinct microtubercles on its hind legs, similar to those used by spiders to direct and manipulate their silk. Trigonotarbids are not considered true spiders, but are accepted as an independent group of arachnid not directly ancestral to modern spiders.
1.1.1 The Mygalomorphae:
This name is given to the group of families that are considered to be comparatively primitive. Spiders have two pairs of book lungs on the underside of the abdomen, fangs that operate vertically in a paraxial fashion and no obvious female epigynum. They usually live in burrows either in the ground or in crevices in tree trunks because they cannot tolerate conditions that lead to desiccation (drying out). Mygalomorphs have compact spinnerets, blade like fangs and two pairs of book lungs similar to ancestral ground existing spiders.
1.1.2. The Araneomorphae:
This name given to the spider families that are considered modern spiders (or advanced) and can tolerate showing habitats that support desiccation. Araneomorphs have only one pair of booklungs, fangs that operate in a pincer-like biaxial fashion and a distinctive epigynum on the underside of the female abdomen.
1.2 Morphology of spiders:-
Spiders occurs in large range of size and color the smallest dwarf spider of subfamily Erigoninae are less than 1 mm in body length while the largest and heaviest spiders occurs amongst Tarantulas with body length up to 90mm and leg spans up to 250mm. Many people confuse spiders with insects. The easy way to recognize the spider from an insect is that spider has 4 pairs of legs and an insect has 3 pairs. One major difference is that insects have compound eyes whereas the spider has singular eyes with lenses. Unlike insects, spiders do not have antennas. Spiders are predatory invertebrate animals that have two body segments, eight legs, no chewing mouth parts and no wings. Spiders are beautiful in structure, with remarkable habits and complex life histories,
Kingdom – Animalia
Phylum -- Arthropoda
Subphylum – Chelicerata
Class -- Arachnida
Order -- Araneae ( Clerk, 1757)
The body of a spider has two distinct parts. The first, front, part consists of a fused head and breast part, called as prosoma or cephalothorax. It is made from a hardened material, called chitin. The second, rear, part is the soft abdomen, called opisthosoma. A tiny tube called pedicel connects the cephalothorax and abdomen. The eight legs, the two jaws (chelicerae) and the two feelers (palps) are connected to the prosoma. The males have a bulb at the end of their palps. These are filled with semen before copulation and are used to inject the semen into the sexual organs of the female. Some spiders have six eyes but most of them have eight eyes located on the front of the prosoma.The back or top of a spider is the dorsal side and at the bottom is called the ventral side. The genitals of the female spider (epigynum) are located just behind the legs on the ventral side.
Fig: - 1. Morphology of Spider
1.2.1 Cephalothorax:-
All spiders has a fused head and thorax called cephalothorax or prosoma, is a complete fusion of the segments but in an insect there are two separate tagmata, the head and thorax. The rear tagmata are called the abdomen or opisthosoma. In spiders, the cephalothorax and abdomen are connected by a small cylindrical section, the pedicel. The shape of cephalothorax is variable from species to species. The cephalothorax is dorsally covered by hard sclerotic shield, the carapace, and ventrally by the sternum. The legs are articulated in the pleural membrane between the lateral edges of the carapace and sternum.
Eyes of spiders
Cephalic region of spider has six to eight simple eyes. The eyes are generally of two types black or diurnal and white or nocturnal. The eyes are arranged in a double row namely anterior row and posterior row. The cephalic area occupied by eye is called as Ocular area.
The eyes of spider differ greatly between families. Spiders who hunt without a web like wolf spiders (Lycosidae), lynx spiders Oxyopidae) and jumping spiders (Salticidae) have a well-developed eye sight. Jumping spiders can see nearly as well as humans. Experiments have shown that they are even capable of seeing colors. Cave spiders, which live in the dark, have no or hardly any eyesight. They depend completely on sound and feeling. The structure of the eye is in basic similar to our eye; behind a single cuticular lens lays a cellular vitreous body and the visual cells. Together with pigment cell this forms the retina. The spider has two types of eyes; the main eyes are always the middle largest ones of the eight eyes the most spiders possess. The main eyes at the front of spiders heads are pigment cup ocelli that are capable of forming images. (Ruppert, et. al. 2004). There are few families of spiders with six eyes. Sometimes the secondary eyes have a light reflecting layer (tapetum). This can be easily observed if one shines with a light in the eyes of a spider during the night. Orb weaving spiders, like the Araneus diadematus, have very small eyes. They do not depend heavily on their eyesight to catch their prey. They have a good developed feeling mechanism that makes them capable of detecting the movements in their web. Spiders detect smell with scent sensitive hairs located on their legs. A spider feels their prey with chemo sensitive hairs on their legs and senses if the prey is consumable.
Chelicerae: -
The chelicerae are the first pair of appendages of the cephalothorax. The chelicerae has curved fang at its tip and at inner side it may be denticulated with groove having tooth on each side. The outer row of these teeth are called as promargin and inner row as retromargin.
Pedipalps: -
The pedipalps are the second pair of appendages of the cephalothorax the palp is composed by six segments namely coxa, trochanter, femur, patella, tibia and tarsus. In mature males the tarsus of palp is modified as copulatory organ. The structure of mature male palp is very important for generic or specific identification of spiders.
Legs: -
In all spiders there is four pair of legs designated as I, II, III and IV respectively each leg is composed of seven segments, namely coxa, trochanter, femur, patella, tibia, metatarsus and tarsus. There must be a difference in the structure of the legs between families.
For example, there are thousands of fine hairs on the tarsi of the wolf spider. Every hair sticks to the smooth surface. Orb weaving spiders have claws on their tarsi. This is the reason they cannot climb on smooth surfaces but are very capable of hanging on threads. The spider grabs a thread with its middle claw and squeezes the middle claw against rough bristles, situated opposite the claw. This gives a solid grip. To release the thread the claw is superior and the bristles push back the thread. The movement of the legs of a spider is partly hydraulic, partly by muscles. The spider stretches its legs by raising the blood pressure in the legs. A jumping spider can create a force that makes them capable of jumping 25 times of their total length. This hydraulic system works excellently for the jumps. Leg expansion in spiders can be done by hydraulic pressure and jumping spiders are able to reach relatively large distances by use of their hind limbs only (Parry and Brown, 1959a; Parry and Brown, 1959b)
Spiders can generate pressures up to eight times their resting level to extend their legs,( Parry, and Brown,1959)
1.2.2 Abdomen:-
The abdomen may be united to the cephalothorax by a narrow pedicel-the seventh somite, and is usually without appendages. The abdomen is pitted dorsally and ventrally by a few pairs of scars called sigilla, which mark the point of attachment of a series of internal dorso ventral muscles. (Tikader, 1987). The abdomen is produced posterior into a conical anal tubercle and bears three pairs of spinnerets ventrally and called as first or anterior pair, second or median pair and third or posterior pairs of spinnerets. Each spinneret has many spigots, each of which is connected to one silk gland.There are at least six types of silk gland, each producing a different type of silk. Silk is mainly composed of a protein very similar to that used in insect silk. It is initially a liquid, and hardens not by exposure to air but as a result of being drawnout, which changes the internal structure of the protein. (Vollrath, and Knight, 2001).
The ventral side of abdomen has one or two pair of book lungs followed by one or two pair of spiracles with transverse fold of epigastric furrow called epigyne the female genital opening.
Spiders are separate group from insect placed under class arachnida, which also include scorpions, pseudoscorpions, solpugids, ticks, and mites. Spiders often confused with Harvestmens which belongs to order Opiliones. Sometimes ant like spiders or beetles like spiders are also confused with insect. Spiders are separated from other arthropods by the following charecters( Kaston, 1978)
Character | Spiders | Insect |
Body region | Two | Three |
Antennae | Absent | One Pair |
Legs | Four Pairs | Three Pairs |
Pedipalps | One pair | Absent |
Poison apparatus | Opening on fangs of Chelicerate | If present usually opening at posterior end of abdomen. |
Wings | Absent | One or two pairs in pterygotes |
Eyes | Simple ocelli generally 6or 8 | Generelly 1 pair of compound eyes with 2 or 3 oceli. |
1.3 Diversity and abundance of spiders:-
Spiders are one of the most diverse animal groups in the world. Various types of spiders can easily be found in a small area. India is also rich in both flora and fauna and is a mega diverse Country. Information about the diversity, distribution and abundance of spider in India is very rare. Studies of spiders are always remained neglected. They are largely been ignored. Spiders serve as bio-control agents (CIKS 2002). Spiders regulate the terrestrial arthropod population as they are important predators (Reichert and Bishop, 1990; Coddington and Levi,. 1991)
Spiders are abundant in number and are ecologically important in almost every terrestrial and semi-terrestrial (wetland) habitat on Earth, from cold Tundra and Alpine ecosystems to tropical rainforests and deserts. There are about 45,776 species under 3974 genera distributed over 114 families (WSC, 2016). In India they are represented by 1686 species belonging to 438 genera of 61 families (WSC, 2015; Keswani et al., 2012). Keswani et al., (2012) identified and described spider species which correspond to only a small number of their total diversity Numbers often go beyond 100 per square meter, which is equal to 1 million spiders per hectare (Colemanand Crossley, 1996). Some species are found on the shores of the ocean and some dive into ponds and streams in search of prey-members of one Eurasian spider family (Argyronetidae) even live underwater in smooth "diving bells" which they fill with air brought from the surface clinging to their hairy abdomens. Spiders are found high up on Mount Everest, and some of the most northerly animals are spiders, as well.
1.3.1 Diversity and Abundance of Spiders in Various Agro ecosystems:-
Arachnids are an important but generally poorly studied group of arthropods that play a significant role in the regulation of insect and other invertebrate populations in most ecosystems (Russell-Smith, 1999). Spiders are habitual to each and every favorable ecosystem with great diver’s conditions and their role in varies according to their diversity. It is studied that the Green plant hopper and Brown plant hopper are considered the most important pests in rice and their populations were always altered in irrigated rice field. In India for many years, insecticides were widely used to control rice pests but the continuous use of pesticides cause many side effects including loss of biodiversity, toxicity, the recovery of insect pests and environmental pollution (Heinrich and Mochida, 1984; Ganeshkumar and Velusamy, 1996; Holland et al., 2000; Amalin et al., 2001; Lu Zhong-xian, 2007). Due to these constraints, researchers developed an alternative, economical and eco friendly method of insect control (Venturino et al., 2008; Chatterjee et al., 2009). The researchers studied that spiders in rice field can play an important role as predators pests which also reducing plant hoppers and leafhoppers (Chiu, 1979; Visarto Preap, 2001; Lu Zhongxian, 2006) Some workers also studied the predatory nature of spiders in rice ecosystem (Samiyyan, 1996; Sahu et al., 1996; Pathak and Saha, 1999; Bhattacharya, 2000; Sigsgaard, 2000; Vanitha, 2000; Mathirajan, 2001; Jose, et al., 2002; Satpathi, 2004; Sudhikumar et al., 2005; Sebastian et al., 2005; Motobayashi et al., 2006). According to Bhatnagar et al. (1982) and Peter (1988), the crop having more insects or insect visitors always had more spiders.
Kapoor, (2008) investigated spiders in coffee fields also with great diversity from westerns ghats.
1.3.2 Abundance of spiders in citrus argoecosystem:-
Citrus is the most important fruit crop of Central India. Upper Wardha Dam situated on Wardha river basin surrounded by various in which cotton and citrus are particularly grown as cash crops. The diversity of spiders was extensively studied to know the occurrence of various species which are preying on the pest on orange trees. Spiders play an important role in regulating insect pests in agriculture ecosystems (Nyffeler and Benz, 1987; Nyffeler et al., 1994; Sunderland, 1999). Studies of Hamamura (1969); Sasaba et al. (1973); Gavarra and Raros (1973); Samal and Misra (1975); Kobayashi (1977); Chiu (1979); Holt et al. (1987) and Tanaka (1989) clearly described the role of spiders as predators in reducing insect pests in rice fields. Muma, 1975; Carroll, 1980; Mansour and Whitcomb (1986); Van Den Berg et al.,1992; Breeneet al., 1993; Amalinet al. (2001a;b); Ghavami Ghanadamooz (2008) and Tahir, et al. (2011) investigated diversity and habitat use by spiders in citrus ecosystem in Florida, California, Israel, South Africa, Texas, Florida, Iran and Pakistan respectively. Similarly many of the pests that occur on citrus in South Africa are under effective biological control (Bedford, 1978). However, the natural enemies of a few others, like the citrus psylla, are unable to keep these pests below the economical threshold. The adult citrus psylla, Triozaerytreae (Del Guercio) (Hemiptera: Triozidae) is the only known vector of the greening disease of citrus in South Africa (McClean & Oberholzer, 1965; Catling, 1970). Production loss due to greening has been estimated at Rands 35 million annually (Van den Berg et al., 1987b). Large numbers of spiders are often present in citrus trees as reported in other countries (Shulow, 1938 ; Carroll, 1980; Mansour et al., 1982; Mansour &Whitecomb, 1986) and in South Mrica (CatIing, 1970; Van den Berg et al., 1987a). Several unidentified spider species have been observed to prey on the citrus psylla (Vander Merwe. 1923; Catling & Annecke, 1968; Catling, 1970) while Van den Berg et al. (1987a) observed many species of spiders preying on adult citrus psylla and they expressed the opinion that spiders are possibly the most important predators of this pest.
Aphids under favorable condition can grow very quickly and causes damage to citrus tree during the growing seasons. Citrus white fly is usually found feeding on the base of the tree level. To feed on the citrus tree, the white fly also lays their eggs on underside of the leaves when eggs hatch, the juveniles are small oval and being sucking the sap from leaves and damages the whole citrus tree. Orange dog caterpillars are the caterpillar attaches to citrus tree by eating the tree’s leaves. The adult butterfly lays her eggs on new citrus leaves and as the eggs hatch and new caterpillar emerges, they can very rapidly defoliate an entire tree in on a few days. Citrus thrips are a tiny orange or pale yellow insects that attacks the citrus tree, they mainly attacks on young leaves and juvenile fruits and feed on the tree’s sap. Brown soft scale is a common problem on citrus tree; these insects are small, non mobile and remains attached to the wood, foliage and sometime to fruit. The citrus bud mite generally attacks lemons; it is small elongated insect which affects whole lemon tree. Citrus red mites can also infect the leaves and fruits of citrus tree. (www.citrus –tree –care.com)
Very little work has been carried out to study the spider diversity in Citrus agro-ecosystem from India and hence this is the primary attempt made by us.
1.4 Predatory Nature of Spiders in :-
In India insecticides are widely used to control rice pests from many years. The continuous use of pesticide has caused many side effects, including loss of biodiversity, the problem of secondary pests, insecticide resistance, toxicity, and environmental pollution. Recently, many efforts have been made to combine various non chemical control methods with insecticides in systems of Integrated Pest Management (IPM). One such effort is the combined use of natural enemies with insecticides. Many uses of parasitic and predatory natural enemies to control agricultural pests have been reported (Van den Bosch et al. 1992).
Spiders are carnivorous arthropods and most abundant predators of insects of terrestrial ecosystems (Edwards et al., 1976). Spiders play an important role as stabilizing agents or regulators of insect populations in agro, forest and other terrestrial ecosystems. Thus their presence in an ecosystem may influence the population of other arthropods in fields. They are predators of pest and kills a large number of insects from their surroundings and hence has a great importance in reducing and preventing the insect pests in agriculture (Sunderland et al., 1986). Spiders feed on insects and some other arthropods and playimportant roles in pest's control. Most of investigations on spiders are inagricultural ecosystems in Iran from rice field, Pakistan from Citrus and from India in Cotton fields. Some researchers were performed on spider fauna and abundance of rice fields (Ghavami, 2004), oliveorchards (Ghavami, 2006d and Ghavamiet al., 2007b), Rose fields (Ghavami and Nematollahi, 2006c) citrusorchards (Ghavami, 2006 a, b; Ghavami and Ghanadamooz, 2008b) and cotton fields (Ghavamietal., 2007b and 2008a and Ghavami, 2007a). Spiders consume a large number of preys, anddo not damage plants. Hence spiders have been considered important predators which help regulate the population densities of insect pests (Pickett et al.1946, Dondale 1956, Duffey 1962, Kajak et al.
1968, Fox and Dondale 1972, Tanaka 1989). Spider communities in areas with at emperate climate achieve equilibrium in the control of agricultural pests (Riechert 1982). In spite of this, they have not usually been treated as an important biological control agent, because there is so little information on the ecological role of spiders in pest control (Turnbull 1973, Riechert and Lockley1984). Some research has shown that spiders in rice fields can play an important role as predators inreducing the densities of plant hoppers and leafhoppers (Hamamura 1969, Sasabaet al. 1973,Gavarra and Raros 1973, Samal and Misra 1975,Kobayashi 1977, Chiu 1979, Holt et al. 1987, Tanaka1989).