WTF?! I was under the bus shelter when a high pitched squealing started, I kinda sounded like the noise you get from burning and dripping plastic.
On further investigation the shrill appeared to be coming from a webbed ball of spiders eggs. Beside the ball was a tiny web-cave with a dutiful parent on guard.
Is this Twilight Zone spookiness a usual thing for baby spiders to do? What was going on?

[youtube]http://www.youtube.com/watch?v=kqYDRxdgnC0[/youtube]

Did you kill it with fire? It almost always works.

I have never heard of screaming spiders. Maybe it was like how grasshoppers do that thing with their legs and it makes a noise.

Kill them?! Fucking no I did not. The only killing I do is bacon.

Ironclad wrote:WTF?! I was under the bus shelter when a high pitched squealing started, I kinda sounded like the noise you get from burning and dripping plastic.
On further investigation the shrill appeared to be coming from a webbed ball of spiders eggs. Beside the ball was a tiny web-cave with a dutiful parent on guard.
Is this Twilight Zone spookiness a usual thing for baby spiders to do? What was going on?

If they were making a noise, then it would have been either through rubbing bristles on their legs, or maybe by twanging strands of silk. Spiders don't have vocal chords, or the ability to inhale and exhale, so they weren't squealing!

Next time I shall capture the oddness on my phone and post it up. Creepy thing, like the end scene of The Fly, the 1958 movie.

Holy smoke, its demonic
[youtube]http://www.youtube.com/watch?v=Et--lFINQOM[/youtube]

That is damn close to the sound these things, or the watchful parent, gave off.

Why's the other spider not legging it? Was it dead?

Spearthrower wrote:Why's the other spider not legging it? Was it dead?

It was probably turned on, mate. Hell, with all that rock n roll throbbing through your hairy abdomen, so too would you be.

First of all, since many spiders rely upon directional vibration sensing to determine where prey or threats are present, it's hardly surprising that they would utilise vibration for signalling. Sound, after all, is nothing more than the vibration of air molecules arising from other molecules in motion.

Second, quite a few spiders utilise stridulation as a means of signalling. Numerous species belonging to the Family Theraphosidae, the Family that contains the large "bird eating" spiders amongst others, utilise stridulation for a number of reasons. Theraphosa leblondi, the Goliath Bird Eater, for example, uses stridulation as a warning to potential attackers to back off, before unleashing its defensive weaponry, which in the case of this and numerous other Theraphosids, consists of 'hair-kicking' - stroking the rear legs vigorously against the abdomen, in order to dislodge abdominal hairs into a cloud in the attacker's face. The hairs of Theraphosid spiders are coated in irritant chemicals called kinins, which in some species are capable of raising blisters on human skin - Acanthoscurria geniculata is a classic example of a spider whose irritant kinins are particularly powerful. Spider keepers exercise considerable caution if they have to handle the known 'hair-kicking' species. Usually, the spiders engage in stridulation as an audible warning of what is to follow, as a means of dissuading threat organisms from pursuing the matter further. Here's a video clip of a Theraphosa leblondi stridulating and warning a potential 'attacker' (in this case the owner's feeding tongs). If the warning isn't heeded, the next step is for the spider to perform a rapid 180° turn, and kicking a shower of irritant hairs toward the thread before making good its escape. Video clip follows:

[youtube]http://www.youtube.com/watch?v=wjrpdGFyCoA[/youtube]

Many of the large South American species engage in this behaviour, including members of the Genera Xenesthis, Acanthoscurria, Pamphobeteus, Lasiodora and Megaphobema, all of which are large spiders.

The video clip posted by DoctorE, on the other hand, features entirely different spiders, namely small jumping spiders belonging to the Family Salticidae. These spiders possess excellent vision, and the males engage in elaborate limb-waving displays in order to signal to females an invitation to mate. However, since these spiders are usually amongst the smaller members of the Class Arachnida, you need specialised equipment to hear any noises emanating from them, and given their size, most of the sounds emanating from the smaller species will be in the ultrasound range of human hearing anyway, so you'll not only need sensitive microphones to pick up any sounds they make, but a frequency shifter to shift the detected sounds into the audible human range.

This scientific paper is one of a number on the subject, viz:

Communication Via Substratum-Coupled Stridulation And Reproductive Isolation In Wolf Spiders (Araneae: Lycosidae) by Gail E. Stratton & George W. Uetz, Animal Behaviour, 31(1): 164-172 (February 1983)

Stratton & Uetz, 1983 wrote:Abstract

Our studies of a new spider species, Schizocosa rovneri (Uetz & Dondale), and its sibling species, S. ocreata (Hentz), provide an example of how sexual communication functions as a species isolating mechanism. Sexual communication by substratum-coupled stridulation proves to be a critical factor in the reproductive isolation of these species. In laboratory pairings, males of both species court conspecific and heterospecific females indiscriminately. However, females only respond receptively and copulate with conspecific males. A forced mating technique that employed anaesthetized females tested for interfertility. Heterospecific pairings of female S. rovneri with male S. ocreata and female S. ocreata with male S. rovneri resulted in the production of egg sacs and offspring in each case. We designed a series of experiments to isolate the various components of sexual communication in S. rovneri. For the male S. rovneri, olfactory and/or tactile cues from the female's silk are sufficient to release courtship behaviour. For the female S. rovneri, substratum-coupled sound production (stridulation of the male palps) is necessary and is by itself sufficient to induce receptive behaviour.

The behaviour described above, in effect, consists of a male spider of the species in question drumming upon the supporting surface upon which he is standing, in order to signal to the female that he is a potential mate as opposed to a potential meal. Presumably, from the limited information in the abstract (why, oh, why are interesting papers like this behind stupid fucking paywalls?), different species have different drumming patterns, allowing females to determine that they are being courted by a male of the correct species.

The same authors also published this paper:

Acoustic Communication And Reproductive Isolation in Two Species Of Wolf Spiders by Gail E. Stratton & George W. Uetz, Science, 214: 575-577 (30th October 1981) [Abstract available here]

Stratton & Uetz, 1981 wrote:Abstract

Sound production by male wolf spiders during courtship is critical for behavioral reproductive isolation of two sibling species. Females only respond to and copulate with conspecific males, and acoustic signals through a substrate are necessary to induce receptivity. No reproductive barriers that could arise during mating (such as genital or mechanical incompatibility) or after mating (infertility) are in effect between the species, since forced interspecific matings produce viable offspring.

Additionally, we have this paper, connected with Salticid jumping spiders of the sort featured in DoctorE's video clip above:

Sound Production And Associated Morphology In Male Jumping Spiders Of The [i]Habronattus agilis Species Group (Araneae: Salticidae)[/i] by Wayne P. Maddison & Gail E. Stretton, Journal of Arachnology, 16: 199-211 (1988) [Full paper available for download here]

Maddison & Stretton, 1988 wrote:ABSTRACT

Stridulating male jumping spiders in the Habronattus agilis species group have a file on the back of the cephalothorax and stout, curved setae on the front of the abdomen . Compared to non-stridulating Habronattus species, stridulators have modified sclerites around the pedicel, and much more massive muscles running from the lorum to the dorsal carapace apodeme and from the side of the pedicel to the epigastric plate, Sound mostly below 3500 Hz is produced during courtship when the abdomen is vibrated up and down against the back of the carapace. When most of the scraper setae are ablated, the sound is diminished . Stridulation may have evolved from the common salticid behavior of abdomen twitching.

We also have this paper (again, behind a paywall - sigh):

A New Mechanism Of Sound Production By Courting Male Jumping Spiders (Araneae: Salticidae, Saitis michaelseni Simon) by D. T. Gwynne & I. R. Dadour, Journal of Zoology, 207(1): 35-42 (September 1985) [Abstract available here]

Gwynne & Dadour, 1985 wrote:Male Saitis michaelseni Simon (Araneae: Salticidae) produce sounds during courtship which can be heard several metres away. Courting males stridulate on dead leaves and are positioned on the opposite side of the leaf from the female. The courtship display contains both visual and acoustic elements. Courtship consists of three phases. In the first two phases, the male stridulates, and in the third phase, in which he makes tactile contact with the female, he alternates bursts of stridulatory sound with bouts of percussive sound in which the first pair of legs strikes the substratum. Stridulation apparently results from the thickened bases of short hairs on the anterior part of the abdomen moving over two files on the posterior part of the carapace. This stridulatory mechanism has not been previously reported for salticid spiders. The frequency spectra and amplitude modulation patterns of sounds produced by stridulation and percussion are presented.

Hmm, looks like my view that the sounds would not be audible to humans in Salticids needs revising in the light of the above! Nice to know I can still learn something!

However, one paper that is available in full is this one:

Marchena And Other Jumping Spiders With An Apparent Leg-Carapace Stridulatory Mechanism (Araneae: Salticidae: Heliophaninae And Thiodininae) by Wayne E. Maddison, Bulletin of the British Arachnological Society, 7(4): 101-106 (1987) [Full paper downloadable from here, along with 3 other sources]

Maddison, 1987 wrote:Summary

The western North American jumping spider Marchena minuta (Peckham & Peckham) is redescribed: Marchena sissonii Peckham & Peckham and Sitticus synopticus Chamberlain are synonymised with M. minuta. Marchena and the Neotropical Genus Helvetia are here considered to belong in the Subfamily Heliophaninae, otherwise known only from the Old World, for they share with the Heliophanines a row of setae-bearing tubercles on the first leg, and rugose carapace sides. These two structures are well placed to function as a leg-carapace stridulatory mechanism. Stridulation may function in social communication in these possibly-communal jumping spiders. The Thiodinine Cotinusa has a similar leg-carapace stridulatory mechanism.

Introduction

This paper began as a review of the little-known jumping spider Genus Marchena of western North America, and indeed much of the paper still consists of a redescription of the single species, Marchena minuta. However, the discovery of peculiar tubercles on the femora of the first legs led me to expand the study to include a search for close relatives of Marchena. I found the tubercles of the Neotropical Helvetia, a Genus studied by Galiano (1963,1975, 1976), and in many of the Old World Heliophaninae, a Subfamily recently studied by Prószyński (1983a, b, 1985), Andreeva et al (1984) and their co-workers. These tubercles not only suggest a Subfamilial placement for Marchena and Helvetia, but they also appear to be part of a stridulatory mechanism. Previous reports of sound production by Salticids (Ewards, 1981; Maddison, 1982; Gwynne & Dadour, 1985), have described stridulation during courtship, but in the Heliophanines stridulation is probably used outside of courtship and may help maintain a social organisation, as discussed below.

Other sources for the above paper include this and this.

Another paper you can all have fun reading is this one:

Copulatory Mechanism In Holocnemus pluchei and Pholcus opilionoides, With Notes On Male Cheliceral Apophyses And Stridulatory Organs In Pholcidae (Araneae) by Bernard A. Huber, Acta Zoologica (Stockholm), 76(4): 291-300 (1995) [Full paper downloadable from here]

Huber, 1995 wrote:The pholcid spiders Holocnemus pluchei (Scopoli, 1763) and Pholcus opilionoides (Schrank, 1781) are investigated with respect to functional morphology of their genital organs using freeze-fixation of spiders during copula in liquid nitrogen and subsequent preparation of histological serial sections of the copulatory organs in functional contact. Special attention is paid to the mode of male pedipalpal arrestation before copulation, which is achieved in two quite different ways: in Pholcus by contact of the lateral cheliceral apophysis with the pedipalpal trochanter-apophysis, in Holocnemus by locking the pedipalpal trochanter between chelicera and pedipalpal coxa. The condition in Pholcus is considered to be apomorphic and to present a synapomorphy of about a dozen genera for which the name “Pholcus-group” is proposed. The stridulatory apparatus of Holocnemus pluchei is described, its biological significance discussed and an overview of accounts on stridulation in Pholcidae given.

Next, we have this paper:

Sexual Selection, Male Morphology, And The Efficacy Of Courtship Signalling In Two Wolf Spiders (Araneae: Lycosidae) by Sonia J. Scheffer, George W. Uetz & Gail W. Stretton, Behavioural Ecology & Sociobiology, 38: 17-23 (1996) [Full paper downloadable from here]

Scheffer et al, 1996 wrote:Abstract Males of the brush-legged wolf spider, Schizocosa ocreata (Araneae: Lycosidae), possess a conspicuous male secondary sexual character: dark pigmentation and tufts of bristles on the tibiae of their forelegs. We tested several hypotheses relating to the role of this conspicuous trait in sexual selection. Triad mating experiments suggest that the tufts do not play an obvious role in the operation of sexual selection by either male competition or female choice, as there were no significant differences in the mating success of intact and experimentally shaved males. However, females mated more often with males that initiated courtship first, suggesting that capture of a female’s attention by male signalling may play a critical role. In behavioral experiments that paired a single male with a female in arenas that allowed both visual and vibratory signal transmission during courtship, female receptivity did not vary significantly with the presence or absence of tufts. However, experiments that isolated the visual component of communication (by eliminating vibratory communication) revealed a significant effect of the presence of tufts: females showed receptivity less often to males with tufts removed. Female response to visual signals was much greater in S. ocreata than in its sibling congener, Schizocosa rovneri, which lacks male tufts. We hypothesize that the tufts serve to increase the efficacy of visual displays of S. ocreata, as vibratory communication is constrained by the complex leaf litter habitat of some populations. Such environmental constraints may make visual signalling over distance a critical factor for effective courtship communication, which may in turn strongly influence male fitness.

Finally, I'll leave you all with this paper:

Vibration In Heteropoda venatoria (Sparassidae): A Third Method Of Sound Production In Spiders by Jerome S. Rovner, Journal of Arachnology, 8: 193-200 (1980) [Full paper downloadable from here]

Rovner, 1980 wrote:ABSTRACT

Pheromone-stimulated Heteropoda venatoria (L.) produce sounds during bouts of leg oscillation whilst coupled to the substratum by their tarsal adhesive hairs. No stridulatory organ is involved. Preventing palpal percussion and abdominal vibration does not eliminate primary sound production. Leg oscillation rates of 63, 83 and 125 Hz, roughly estimated from high speed cinematographic samples of signalling, were within 1 SD of the mean frequencies of the lowest (Y=88 Hz) or highest (Y-=146 Hz) wave-trains, as indicated by oscillographic analysis of such sounds. These signals resemble and are analogous in origin to insect flight-sounds, the fundamental frequency being determined directly by the appendage oscillation rate. Hypotheses about the role of vibration in these and other spiders, including Araneids, are considered.

So there you have it. Everything you ever wanted to know about spider stridulation.

Super feedback as usual, Cali. Many thanks. I wonder if my shadow urged the parent to stridulat (-e?) defensively.

Anyhoo, mystery effectively solved.

bookmarking

[youtube]http://www.youtube.com/watch?v=NAKyokwktsI[/youtube]