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Meeting of the 22nd Jan. 1843 p 349 vol. IV R Westring Kroyer's Naturhistorisk Tidskrift

We know from the examination of singular and various insects that at least some few kinds of the smallest kinds of insects can produce either a humming or creaking noise, Was this of the animals free will, or likewise in the captive state, when irritated with the fingers or other object, when tormented, struck upon a pin this insects, which can produce the creaking noise by means of the friction of two parts against one another, are we know always possessed of a harder covering in the parts, wh. rub together,

It must consequently appear surprising to us, on the first thought on the subject, that amongst the European spiders […] which we know are furnished peculiarly with respect to the abdomen) with quite a soft covering yet such a kind can be found, and what it be able similarly with all other

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Insects with harder coverings to produce a creaking sound;

Considering that the body is made in so slight a fashion, namely, only of two visible (literally "in the eye falling") principal parts of which the anterior consists of head & thorax completely grown together into one piece, and the posterior consists of the soft abdomen which is fastened with the thorax only by means of a small fibre; considering this, it seemed as first difficult to us to find by what means the creaking noise could be produced.—

The beetle which afforded me the occasion for the investigation of the power of stridulation in question, the same which was first described by Herr Schranck under the name Aranea Serratipes and likewise was described "as quite a different spider"? by Prof. Sundercall in the Roy. Swedish Acad. Sci. 1831, p. 133

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under the name Drassus phaleratus (Panz); Whose generic name according to the above professor's Conspectus Arachnidum 1831. p. 19 ought…to be separated from the genus Drassus & to obtain a name "Asagena" to itself.—

When the above spider (male) was caught by me at Gottenburg some years since, I observed that the thorax, as in some of the nearly related kinds among the genus Theridion, rather unusually was hard covered with a fine shagreened (Thorax with)[in Darwin's hand] surface, except the most outside base which was smooth & shining; but observe: the base of the abdomen was surrounded, about the fibre which joined it with the thorax, but a somewhat raised (& living)[in Darwin's hand]  border, which in the margin margen was finely serrulated serrulerad.—

As the spider likewise had the edge margen of the thorax finely serrulated and besides was

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Furnished with rows of teeth along the leg, and as both these peculiarities did not lead to the supposition of any purpose with respect to the animals mode of life, connected there with — as this was so — neither could I by the knowledge of the existence situation? Of the serrulated border set down any excessive purpose as belonging to it; and because the animal was killed before the sticking on the pin, there was no opportunity on that occasion for the experiment which was tried afterwards.—

Last year (1841) it happened that I caught 3 specimens, which were all males like the previous one.—

The females seem to be rarer, for even in summer I have caught several specimens, but they were entirely males. I presume then that the males seem more numerous merely on the following account,

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that they are more often found wander about in the grass, probably seeking at the pairing season after the females which seem rather to keep themselves there under some stone or hiding place.—

When I had taken the specimen out of the small paper, shaped like a thimble, which I employ in collecting spiders, and had stuck the spider upon a pin I thought that I observed a creaking noise. I thought at first that this noise arose from a beetle which stood in the collecting box on the table; the noise was renewed & I thought that it now came from the spider, which I held between my fingers at the time.

I now remembered the discovery which I had made some years before of the serrulated border, & I now reflected that the noise might be occasioned by

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The rubbing of the serrulated border against the thorax. I withdrew for greater certainty from  the collecting box & went to the window & also touched the spider's abdomen with my finger.

He began then at once & frequently to wriggle his abdomen up & down, whereby he rubbed the serrulated border against the smooth base of the thorax and at the same time was the sound now heard, which still more markedly was strengthened by this, that I stuck a pin against a piece of paper right into this spider's body.—

I stirred up the two other papers and with a pencil pressed on the remaining spider's thorax & the same noise was heard afresh & somewhat stronger in consequence of the resonance of the paper bag.—

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The noise appeared almost the same as that which we hear produced by Cerambycidae & Lepturetae, Reduvius personatus &c.; but compatibly with the smaller size of the spider's body, somewhat weaker.—

According to the experience we possess of other insects it seems that no case occurs, where the noise is produced by means of the moving of the abdomen against the thorax, but indeed by the contrary process viz: in the Cerambycidae & Lepturetae by means of the under back edge of the thorax against the mesonotum or the smooth piece which like concealed before the scutellum.

In consequence of the above experiment we may hereafter augment with Aptera the list of insects which possess the power to produce the stridulatory

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Noise and in which we hitherto counted the following orders:—

Coleoptera Orthoptera Rhyncota & Hymenoptera.—

How far the females can produce the stridulation I can not exactly discover; but if the only specimens which I possess are as it appears really the females of the species question, I presume that they cannot produce the above noise, although they certainly possess the raised border about the base of the abdomen; but it appears to be not in the least degree serrulated.—

One might believe, althoug' quite by gaels, that, provided we do not give our judgement that insects have no power of hearing, the males whilst they are wandering about in the grass, allow their stridulation to be heard

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in order to entice therewith the females from their hiding place; or perhaps it may constitute the prelude or means of excitement enumerated before the act of copulation.

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[in Darwin's hand:]

What name does he use?

Reduvius - stridulation

Reference:

Westring, R. 1843. Underretning om det af ham opdagede Stridulationsorgan hot en Arachnide, Asagena serratipes, Sehrk. Naturhistorisk Tidskrift 4: 349-353.