The Structure and Habits of Spiders

CHAPTER III.. Spinning-Habits.—Spinnerets.—Spinning-Glands.—Beginning

Spinning-Habits.—Spinnerets.—Spinning-Glands.—Beginning of a Thread.—Holes and Nests.—Burrows of Lycosa.—Trap-door Nests.—Tubes and Nests of Drassidæ.—Webs of Agalena.—Webs of Linyphia and Theridion.—Spiders living in Webs made by Others.—Round Webs.—Epeira Vulgaris.—Zilla.—Nephila.— Habits in the Web.—Curled Webs.—Cribellum and Calamistrum. —Webs of Amaurobius.—Regular Webs of Dictyna.—Triangle Web.—Round Webs with Curled Thread 38

CHAPTER IV.. Growth of Spiders.—Differences Between Male and Female.—

Growth of Spiders.—Differences between Male and Female.— Differences between Old and Young.—Male and Female of Nephila and Argiope.—Heads of Male Erigone.—Palpal Organs.—Epigynum. —Use of Palpal Organs and Epigynum in Various Spiders.—Laying Eggs.—Cocoons of Drassus, Attus, and Epeira.—Cocoons of Argyrodes and Argiope.—Care of the Cocoon.—Parasites.—Growth in the Egg.—Hatching.—Habits of Young Spiders.—Moulting. —Habitats of Spiders.—Distribution of Spiders 86

LIST OF ILLUSTRATIONS.

PAGE 1. Under Side of Epeira Vulgaris 13 2. Foot of Epeira Vulgaris 14 3. Foot of Attus Mystaceus 15 4. Upper Side of Epeira Vulgaris 18 5. Section of Epeira Vulgaris 20 6. Mygale Hentzii 24 7. Dysdera Interrita and Eyes 26 8. Drassus 26 9. Agalena Nævia 27 10. Lycosa and Eyes 28 11. Salticus and Eyes 29 12. Thomisus and Eyes 30 13. Theridion 31 14. Mandibles of Epeira Vulgaris. Front View 33 15. Claw of Mandible 33 16. Spinnerets of Epeira Vulgaris 39 17. Single Spinning Tube 40 18. Spinning-Glands 40 19. Spinneret of Prosthesima 41 20. Spinneret of Agalena with some of the hairs removed 41 21. End of Thread 42 22. Trap-door Nests. Copied from Moggridge 47 23. Nest of Dolomedes 52 24. Web of Agalena 55 25. Web of Linyphia Marmorata 57 26. Web of Linyphia Communis 59 27. Pholcus swinging 61 28. Round Web of Epeira Vulgaris 62 29. Web of Zilla 65 30. Web of Nephila Plumipes. From Wilder 66 31. Part of Web of Nephila, to show the smooth threads. From Wilder 67 32. Epeira Spinea 69 33. Spinnerets of Amaurobius 72 34. Calamistrum of Amaurobius 73 35. Dictyna spinning Curled Web 73 36. Part of Web of Amaurobius 74 37. Part of Web of Dictyna, showing regular arrangement of threads 75 38. Unfinished Web of Triangle Spider. From Wilder 76 39. Finished Web of Triangle Spider, and Spider holding the Web. From Wilder 78 40. Young Lycosa flying 81 41. Flying Spider with a Thread attached to the Ground 84 42. Large Attus flying by a Brush of Threads 85 43. Male and Female Nephila Plumipes. From Wilder, in Proceedings Boston Society Natural History 78 44, 45. Heads of Males of Several Species of Erigone 88, 89 46. Palpal Organ of Mygale 89 47. Palpal Organ of Epeira 90 48. Palpal Organ of Theridion 91 49. Epigynum of Epeira Riparia 92 50. Epigynum of Theridion 93 51. Epigynum of Theridion 94 52. Copulation of Lycosa 95 53. Copulation of Linyphia 96 54. Copulation of Agalena 96 55. Copulation of Epeira Riparia 97 56. Drassus laying Eggs 99 57. Lycosa carrying Cocoon attached to her Spinnerets 100 58. Attus Mystaceus laying Eggs 101 59. Epeira Strix making Cocoon 101 60. Epeira Strix laying Eggs 102 61. Cocoon of Argyrodes hanging by a Stem 103 62. Cocoon of Epeira Riparia. From Wilder 103 63. Eggs during Segmentation 106 64. Eggs further Advanced 108 65. Young Epeira Riparia after First Moult 109 66. Moulting of Nephila Plumipes. From Wilder in Proceedings American Association 111 67. Nephila Plumipes just after Moulting. From Wilder 111

THE STRUCTURE AND HABITS OF SPIDERS.

CHAPTER I.. Anatomy and Classification.

ANATOMY AND CLASSIFICATION.

The spiders form a small and distinct group of animals, related to the scorpions, the daddy-long-legs, and the mites, and less closely to the insects and crabs. They are distinguished by the more complete separation of the body into two parts; by their two-jointed mandibles, discharging a poisonous secretion at the tip; and by their spinning-organs, and habits of making cobwebs and silk cocoons for their eggs.

The common round-web spider, Epeira vulgaris of Hentz, will serve as well as any species to show the anatomy of spiders in general. Fig. 1 shows the under side of this spider; Fig. 4, the upper side; and Fig. 5, an imaginary section through the body, to show the arrangement of the internal organs. To begin with Fig. 1: the body is seen to be divided into two parts, connected only by the narrow joint, A, just behind the last pair of legs. The front half of the body, called the thorax, contains the stomach, the central part of the nervous system, and the large muscles which work the legs and jaws. The hinder half, the abdomen, contains the intestine, the breathing-organs, the principal circulating-vessels, the organs of reproduction, and the spinning-organs. Connected with the thorax are six pairs of limbs, four pairs of legs, B B B B, a pair of palpi, C, and a pair of mandibles, D.

LEGS.

The legs are used chiefly for running, jumping, and climbing; but the front pair serve often as feelers, being held up before the body while the spider walks steadily enough on the other six. One or both of the hinder legs are used to guide the thread in spinning; the spider at the same time walking or climbing about with the other six or seven. The legs are seven-jointed; and on the terminal joint are three claws, Fig. 2, A, B, C, and various hair and spines. In many spiders a brush of hairs takes the place of the middle claw, as in the jumping spiders, Fig. 3. Spiders with these brushes on their feet can walk up a steep surface, or under a horizontal one, better than those who have three claws. The legs of most spiders have among the hairs movable spines, which, when the spider is running about, extend outward at a right angle with the leg, and, when it is resting, are closed down against the skin.

PALPI.

In front of the legs are the palpi, Fig. 1, C, C,—a smaller pair of limbs, with six joints and only one claw or none. They are used as feelers, and for handling food, and, in the males, carry the curious palpal organs, which will be described farther on. The basal joints, Fig. 1, E, of the palpi are flattened out, and serve as chewing-organs, called “maxillæ.”

Mr. Mason has lately described, in the Transactions of the Entomological Society of London, a large spider which has teeth on the inside of the palpi, which, when the spider is angry, are rubbed against teeth on the mandibles, producing a noise.

MANDIBLES.

The front pair of limbs, the mandibles, Fig. 1, D, are two-jointed. The basal joint is usually short and stout, and furnished on the inner side with teeth and hairs. The terminal joint is a small and sharp claw, which can be closed against the basal joint when not in use.

ABDOMEN.

On the under side of the abdomen, just behind the last pair of legs, are two hard, smooth patches, which cover the front pair of breathing-organs, the openings to which are two little slits at Fig. 1, H. Between these is the opening of the reproductive organs, and, in female spiders, the epigynum, Fig. 1, J,—an apparatus for holding the reproductive cells of the male.

At the end of the body are the spinnerets, which will be described in another chapter. There are three pairs of them; but many spiders close them together when not in use, so as to cover up the middle pair. The third pair of spinnerets are often several-jointed, and extend out behind the body like two tails. In front of the spinnerets is a little opening, Fig. 1, K, which leads to air-tubes that give off branches to different parts of the abdomen. At M, Fig. 1, are usually two colored bands, or rows of spots, marking the course of muscles attached to the skin at various points along these lines.

Fig. 4 is the back of the same spider. The head is not separated from the rest of the body, as in insects, but forms, with the thorax, one piece. On the front of the head are eight eyes, Q, which are differently arranged in different spiders. At the back part of the thorax is a groove, P, under which is attached a muscle for moving the sucking-stomach, Fig. 5, d. From this point radiate shallow grooves, that follow the divisions between the muscles of the legs. On the abdomen are several pairs of dark smooth spots, which mark the ends of muscles extending downward through the abdomen. The markings of this spider are very complicated. The spot on the middle of the front of the abdomen is a very common one, and, in some spiders, extends the whole length of the body. The waved lines on each side are also common, and, in long-bodied spiders, often form two bright-colored stripes, or rows of spots, running nearly straight the whole length of the abdomen.

INTESTINE.

Fig. 5 is a section of the same spider. The mouth is at a b, just under and behind the mandibles, and between the maxillæ. It has an upper, a, and under lip, b, each lined with a horny plate, in the middle of which runs a groove. When the lips are closed, the two grooves form a tube, which leads to the œsophagus, c, and so into the stomach. At the end of the œsophagus is the sucking-stomach. This consists of a flattened tube, to the top of which is attached a muscle, d, connected with the groove in the back; and to the bottom, muscles, f, attached to a tough diaphragm spreading across the thorax, and fastened between the legs on each side at g g. When these muscles contract, the top and bottom of the sucking-stomach are drawn apart, and whatever is in the œsophagus sucked in. By this pumping motion the spider is supposed to take liquid food from the mouth, and drive it backward into the abdomen. Just behind the sucking-stomach, the intestine gives off two branches, e e, which extend forward around the stomach muscle, and meet over the mouth. Each of these branches gives off on the outer side four smaller branches, m m m m, which extend downward,—one in front of each leg,—and unite on the under side of the thorax.

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