Art. XXV.—Notes on Nest, Life-history, and Habits of Migas distinctus, a New Zealand Trapdoor Spider.

By J. B. Gatenby.

Abnormal Forms of Nests.

Life-History.

About the months of February and March the female lays from thirty to sixty small white eggs. These are placed between the wall of the nest and a piece of silk stretched across a rounded part of the tube (fig. 10, O, the arrow).

The egg-bag is placed variously in the nest, but in fig. 14 (top) the commonest position is shown. The piece which stretches across the sides of the tube is ⅖in. in diameter. Separate egg-cases, with two sides, not connected to the tube; are rare. The young emerge and lie dormant, inside the case. After a week or so the mother removes the covering,. and often weaves in lieu of it a transparent filament-like veil of silk over them (fig. 10, b).

After the young become strong enough they push out of the covering, and wander out of their old home. Often some few remain with their mother, and frequently are met with as late as the end of April. These must be provided with food by their parent, for they are often a fair size.

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When the young emerge from the parent nest the majority are pounced upon and eaten by an eager, hungry horde of bank-inhabiting, vagabond' spiders. Few escape; those that do proceed to burrow their tiny tunnels and to make their nests. They bite out the earth with their falces, which are very strong. Of course, the state of the earth determines the length of time taken to make the boring. The doors of the nests of young spiders are round, very small, being less than 1/12 in. in diameter, and very difficult to detect. As the spider grows she needs to enlarge her door.

Enlargement of Tube and Door.

If the food-supply is good the spider grows rapidly, and soon the nest becomes too small for her. When she wishes to enlarge her nest she tears away one side of the silken lining of the nest and widens that side in its entire length. She then spins a silk web over this. The door is enlarged as shown in fig 7, a, b, c, d, e. Fig. 7, a, shows a door which has been enlarged once, the original door of the young spider being the circle inside the larger door. Fig. 7, e, shows a door which has been enlarged six times. Nests are seen with nine or ten enlargements.

When the spider wishes to enlarge her door, after having enlarged the tube, she spins under the old door an entire silk layer the size of the newly enlarged tube. The door after a few enlargements becomes very ragged, and hence less conspicuous. The newly spun layer is covered with earth where the edge protrudes beyond the rim of the old door. Where the lids have a thick earthy layer, and only one or two silken ones, the spider cements a rim of earth around the old door and then spins a web underneath it. I believe the spider enlarges her door and tube six or seven times during her life

The Spider's Enemies, etc.

Although encased in a strong tube with a deceptive door, this Arachnid is not free from enemies. The greatest destroyer is excessive heat. In the middle of summer the banks, especially the clay ones, become very hot. Unless the spider is able to capture enough juicy insects to assuage her thirst she soon becomes dusty and emaciated, and ultimately succumbs. Sometimes before she dies, in a last despairing effort to evade the ardent rays of the sun, she weaves a silken partition between herself

and the door (fig. 10, c, the arrow). In many cases she is found dead behind this screen, while her door, after warping with the weather, allows the entrance of all sorts of vermin—woodlice, centipedes, aptera, small spiders, and a large number of other forms of insect-life. These cannot reach her, for the screen shuts them off.

Unless there is an absence of moisture, hunger has no terrors for these spiders, for they are easily able to exist without food for three or four months. Frequently in a famine a spider devours her neighbour, a hard fight always ensuing first.

I have several reasons to suspect that Pompilius fugax, &c., is a keen enemy of M. distinctus. I have caught P. fugax dragging a trapdoor spider across a bank. Whether the spider was caught by the fly by the latter opening the door, or by the spider jumping out to catch the fly and instead catching a Tartar, I know not, but I have more than once found a pupa-case of a small Ichneumon fly lying among the remains of a spider.

The Spider's Age.

This is a question I could not definitely settle, although I have kept specimens three years and a half. Unfortunately, I was obliged to travel to the north for a holiday, and my pets were put with their box in the garden, and when I returned the only remaining member of the thirty spiders was a young one three months old.

I know that some spiders take two to three years to reach maturity, but if the food-supply is short the time may be longer. I have kept mature spiders three years and a half, and possibly they would have lived much longer. Hence the spider may be six or even seven years old when it dies.

The Food of M. distinctus.

This consists mainly of Diptera and small Lepidoptera. The young eat small organisms like Aptera (Podura). While catching her food she shows a cleverness that is immensely superior to that of other sedentary spiders.

On fine sunny days flies and other insects hover about the banks. Now and again they will alight on the bank near a group of nests. The spiders, if they are hungry, keep on the alert; when one hears a fly she creeps up from the bottom of her den, lifts the door slightly, and reconnoitres (fig. 10, b). Whilst peering out the spiders often become rather excited when an unsuspecting fly draws nigh, and this is shown by the rash way in which they sometimes open the door; the fly then discovers its enemy, and escapes. This makes the spider more circumspect, and the next fly that draws nigh is watched more carefully.

The person who is watching the hunting operations of the spider is compelled to admire her great patience, and also the way she controls, with a front leg, the peeping-out space between the door and the rim of the tube (fig. 10, b; notice the bent leg). At last her patience is rewarded: a fly accidentally alights right in front of the treacherous door; the spider throws open the trapdoor and leaps right upon the back of the fly, driving her falces into it (fig. 8). She withdraws quickly into the tube, and pulls the door till it shuts firmly. Then she crawls down to the end of her tube and devours the fly. The capturing takes a very short time, and unless the observer watches closely he will miss the whole operation.

She will seldom dash out unless the fly is right in front of the door. If it is too far away she would be obliged to expose her body to danger while she reopened the door. As it is, her abdomen keeps. the door open, so she soon slips back. When the spider has eaten the fly she drops out of the door those parts which she discards.

I kept thirty spiders in a small box placed on a shelf. On the sunny days when the flies were about I would sprinkle a few grains of sugar in front of each door, and put the box in the sun. The unsuspecting flies would come to feed on the sugar, and would fall easy prey to the spiders. In winter, when few flies were about, on the fine days I would catch house-flies and tie cotton to their wings, and make them walk over the door. The spiders would drag them in, cotton and all. Next day the cotton, with the dry carcase of the fly, would be found often an inchi from the door.

Spiders may be killed whilst attacking an Ichneumon fly inadvertently-This would explain why nests, even in a plentiful insect season, are-found tenantless, except for vermin.

Even when not looking for food, spiders will be caught watching out of their nests. Before they emerge at night they always reconnoitre for an hour or so. If a spider is alarmed she rushes up from the terminus of her tube and proceeds to resist an entrance.

The Spider's modus operandi Whilst Holding Down Her Door.

Four legs (the front pairs) are, together with-the falces, used to fix on the silken underlining of the door. The falces are driven into the middle of the door, the four legs being placed so that the claws hold to the edges of the lid (fig. 12). The thick bristles on the ultimate and penultimate joints of the first two pairs of legs present a spiny array (fig. 1, female; fig. 2, male). (Fig. 3 shows a few of these terminal protective bristles, with the claws.) The remaining pairs of legs are placed around the tube, the claws sticking into the silk lining (fig. 11). All the legs are slightly bent when holding on, so that the spider's hold is elastic, and better able to withstand a jerk. When in this position the spider pulls the door tightly, often exerting a force capable of lifting a half-ounce weight.

Fig. 11 shows the profile of a spider holding her door. It will be noticed how well the spider's abdomen is protected by the curve in the side of the tube.

Sometimes whilst frantically resisting the entrance of an enemy the spider will suddenly let go the door and make as if to rush out on the intruder. If a person has his hand near when this happens he quickly drops the pin with which he has been holding the door, and removes his hand to safety. But this is apparently what the spider wishes to happen, and immediately she turns on her back again (fig. 11) and closes the door. The whole business is a ruse on the part of the spider, for she would not forsake her nest to bite any enemy.

Some spiders relinquish their hold when they perceive that they are weaker than their enemy, but they remain watching nearly hidden around the bend of the nest. Some spiders run to the bottom of their den when beaten at the door, and seek to hide themselves.

In wet weather spiders often remain at the end of their dens even when the door is touched. In captivity spiders often weave some strands

of silk between the door and rim, in order to keep out an intruder (fig. 10, a, near letter D). Sometimes they do this whilst hibernating. If the tube pierces the bank in a downward direction, in order to protect its abdomen while still holding the lid it would be obliged to hinge the door on the bottom side of the open. Consequently the lid would be continually falling open with its own weight. Hence the tube pierces the bank in an upward direction (fig. 14).

Habitat

This spider is seldom found many miles from the sea-coast. The spiders prefer- a sheltered bank, never, as far as I know, burrowing into the ground, as some other trapdoor species.

Spiders of the same species from different localities often show curious differences in habits and manner of building their nests. This is taken into account when I say that the results may be slightly dissimilar if spiders from provinces other than Auckland or Wellington are studied.

I have been disappointed to find that M. distinctus is free from parasitic Acarina.

Explanation Of Plate XV.

• Fig. 1. M. distinctus, female; × 2.

• Fig. 2. “male; × 2.

• Fig. 3. Tarsus of female, front leg, showing bristles.

• Fig. 4. Terminus, female palpus.

• Fig. 5. Male palpus, side view.

• Fig. 6. Eyes.

• Fig. 7. a, young spider's door, and so on to, e, the adult door, from above.

• Fig. 8. Female leaping on back of fly (see fig. 10).

• Fig. 9. Side view of sections of nests, showing different devices for keeping the door from opening too far.

• Fig. 10. Female watching a fly, which is unaware of its danger. (Fig. 8 shows what happened a second later.)

• Fig. 10. a, at D, strands of silk woven to keep the door closed; O shows position of egg-bag (see fig. 14, top). b, at arrow, film of silk woven over young spiders. c, M shows partition often woven by moribund spider.

• Fig. 11. Female holding door against intruder (profile).

• Fig. 12. Same from above, showing position of legs, &c.

• Fig. 13. Nests built under a stone. Both have two doors, one at each end.

• Fig. 14. Top nest with egg-case; middle nest which has been denudated, after which the spider has bored in farther; lowest a nest built near surface on account of hardness of earth. (Fig. 14 also shows a bank in which the nests are in their natural position.)

• Fig. 8, 9, 10, 11, and 12 do not, of course, show true position of tube; they should be as in fig. 14; but if drawings are turned around, the proper effect is obtained.