Wrote Letter 58 of 1687-09-09 (AB 103) to Members of the Royal Society

September 9, 1687
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Text of the letter in the original Dutch and in English translation from Alle de Brieven / The Collected Letters at the DBNL - De Digitale Bibliotheek voor de Nederlandse Letteren.

The original manuscript, written and signed by Leeuwenhoek, is preserved at the Royal Society (MS. 1923. L 2. 8).

Reception in London

Two months after it was written, this letter was read at the meeting of the Royal Society on November 16/26, 1687 (O.S./N.S. Birch's History, vol. IV p. 552, 553-554):

Part of a letter of Mr. Leeuwenhoeck, concerning the generation of ants, was read; wherein he was of opinion, that the white things, taken for their eggs, are really worms, which, he said, he had observed to be hatched into ants in a little time. The rest of the letter was referred to the next meeting.

At the next meeting, on November 23/December 2:

The latter part of Mr. Leeuwenhoeck's letter of September 9, 1687, concerning the generation of ants was read, wherein he concluded three things,

1. That the real eggs of ants are exceedingly small, and not bigger than ordinary grains of sand.

2. That out of these eggs are worms produced, which being without any motion of their own and helpless are fed by the old ants; whence it comes to pass, that they are so busy in carrying food to their nests in summer, and not in order to lay up any magazine of provision against winter, as was vulgarly supposed: and

3. That those which, were most commonly called ants eggs, are either those worms or aureliae of young ants, or else a sort of webs, wherein one sort of ant-worms were observed by Mr. Leeuwenhoeck to wrap themselves a little before their maturity.

He took notice by the way of the manner of the stinging of ants, which he found not to be by biting, as some imagined, but by a real sting in the tail, which is all along on the back thereof grooved with a deep groove not unlike the scheit used by seamen to wet sails withal; by means of which groove the ant conveys to the point of her sting a small drop of venomous transparent liquor, which by its acrimony occasions the smart and swelling, that generally follows the sting of ants.

Birch's History ended the following month, December 1687. This letter is the last one for which we have a record that the Royal Society read it. However, there is no reason to believe that they stopped doing so.

Response to other researchers

In the text, Leeuwenhoek continued his response from the previous Letter 57 to the illustrations in Johann Franza Griendel's Micrographia nova, a Latin-language book published in 1687.

After completing my last missive, I have let my thoughts dwell on ants, and I firmly imagined that, in the so-called ant's eggs, a young ant was made: the more so because I saw that a German author (whom I mentioned in my preceding missive) had shown us a picture of an ant inside an ant's egg, a drawing of which is enclosed herewith, as fig. 1. Which egg was shown (very approximately) as being only one eighth of the size of an adult ant.

The print from Griendel's book is on the right. Leeuwenhoek had his draughtsman re-engrave the ant egg in the lower right, so Leeuwenhoek's Fig. 1 is a reverse image. He suspected that there was something other than a fully developed ant inside that egg, but he was able to approach the question with fresh eyes.

I have nevertheless set aside my own conclusions, and have thought fit to investigate the truth of this for myself, and in addition to discover, if possible, how, and in what way, the so-called ant's eggs might be made to grow.

Specimens and methods: ants in his garden

While Leeuwenhoek examined many things that came from great distances, he could find plenty of ants in his own garden. This garden was outside the walls of Delft, but he never specified where exactly.

Reflecting that in my garden, there was no need for me to be in want of ants' nests since we used to be badly pestered by them, I mixed a whole spadeful of earth with both ants and eggs, laid these on a clean sheet of paper, and sat down in front of it, closely watching the ants (whose habit it is to remove their eggs when one stirs their nest).

From many of them I took away what they were removing; and I observed that what many of them carried away was an ant that was quite white and motionless; while in other, similar ants the whitish color had already changed into a reddish color. Others, again, burdened themselves with a white, longish body, and these I concluded, were the genuine so-called eggs. These latter, I noticed, were - in every sort - as small as a common grain of sand, so that, at first, I only took notice of what the ants were carrying, and took away from them what I judged might serve my purpose.

Away from home, he did not bring one of his powerful lenses.

To that end I had brought with me several small, new glasses, into which I put each separate sort as far as possible; and since I had nothing with me, at the time, but a more than usually magnifying pair of spectacles, I searched (after most of the Ants had run away) the earth (which consisted of a mixture of clay and sand), in which I still found several very small, white particles; but among these I also picked up some particles of sand, which I had mistaken for parts originating from the ant.

If he had spectacles that magnified more than he needed them to for everyday use, then he must have used them when he did not need even the weakest of his ground lenses.

What motivated him?

Curiousity about the world around him. What something happened, he wanted to know exactly what it was. As an off-hand remark in this letter, Leeuwenhoek gave an indication of how long he had been using lenses to investigate nature.

These swellings, which I received from the ants while investigating their reproduction, caused me more pain than they gave me at any other time in the whole of my life, although I have many times been stung by them: For it is now about twenty years ago that, having once been stung hard by the same, I then discovered that the abdomen was provided with a sting.

Twenty years before this letter was written in 1687 was 1667, a year or so after he made a short visit to England. There, he used a lens to look more closely at the chalk on the coast. How powerful were his lenses then? The lens best suited to looking at chalk and at an ant's body would have been much less powerful than the lenses Leeuwenhoek later used for looking at little animals in canal water in the 1670's.

Public reception: "How anybody can let his imagination run away with him."

By the time he wrote this letter, Leeuwenhoek had been struggling for over a decade with people who had not seen what he had seen and thus did not as accurately understand how the world worked. Unlike them, he was always willing to change his ideas based on visual evidence.

I must say that, before this, I never had any other idea than that these worms (which hitherto, in our ignorance, we have always called by the name of ants' eggs), examined with the naked eye, were, in fact, ants' eggs, and that the black spot which we see in the body of these worms, was the small, young, unborn ant.

At the end of the discussion, Leeuwenhoek returned to Griendel. He was not an ignorant Delftenaar, but an educated German, a Capuchin monk and author of several other books. The image on the right is from the book Leeuwenhoek referred to, Micrographia nova. Griendel also died in 1687, which Leeuwenhoek might not have known when he wrote this letter in September of that year.

But what amazes me above all is, how anybody can let his imagination run away with him to such a point that he presumes to have seen in the so-called egg, through the microscope a small, half-grown ant. And, in addition, illustrates the body, head, legs and eyes of the same, whereas, on the contrary, nothing in the world has ever become visible of the worm (which, so far, has always been called an egg), either to him or to ourselves.

He followed that with a summary of what he had observed.

This being so, we have now completely repudiated the common saying, to wit, that the diligence of the ants, which they apply to the carrying of food to their nests, serves only to enable them to live on this food during the winter.

Whereas, on the contrary, it is clear that it is chiefly, nay, who knows, solely, for the purpose of rearing the worms that have come out of their eggs (and are powerless to feed themselves), and bring them food, long enough until they have got so far that they assume the shape of an ant.

He concluded the discussed by asserting his empiricism. If he saw it, it must be so.

I am well aware that these my assertions and observations will meet with very much contradiction; and the more so because so many people have written about the diligence of the ant, and its thoughtful foresight towards the winter: But I will take no notice of that, I express my thoughts as I conceive them myself.


The original drawings are lost. The Dutch and Latin editions that Leeuwenhoek published used the same plate with all eight figures. The one below (click to enlarge) came from the 1730 fourth edition of Continuatio Epistolarum, as did the images on the sidebar. In the text, Leeuwenhoek noted that someone else drew the figures.

Among the smallest parts that I took away from the ants, or sought out from amidst the earth, I found several eggs which were so tiny that I could not recognize them with the naked eye. I have put such an egg before the microscope, and I had it drawn, as is shown here in fig. 2. ABC.

Plate from
Continuatio Epistolarum

Figures 1 - 8

He also did something he rarely did. Still discussing Fig. 2, he spoke of a tool that he used, in this case a ruler.

Furthermore, in order to illustrate the minuteness of such an egg, I laid the same on a graduated ruler; and I am bound to say that ninety diameters of the thickness of one egg do not amount to the length of one inch.

As he had in several recent letters, Leeuwenhoek implied that he and his draughtsman did not always see the same things when he noted that in this case the draughtsman did see what Leeuwenhoek wanted to illustrate. Referring to Figs. 4 and 5, he wrote:

I also had one of these eggs drawn, because the draughtsman was able to recognize all the worms' members in this egg. ... I further put before the microscope one of the Worms which, during the aforesaid time, had crept out of the Eggs, and had it drawn just as it appeared.

Discussing Fig. 6, he noted that the figures illustrated only the beginning of the life cycle of the ant. Oddly enough for someone who had so much difficulty with public acceptance of his ideas, he spoke of how easy these creatures were to imagine.

These worms lie a bit curled up when they are young: But by the time they have grown to almost full-grown size; they begin to straighten out. This worm is drawn through a much less magnifying glass than that through which the preceding figures are drawn, so that one may surely conclude from this how small the eggs are. I might illustrate the size of a full-grown worm through the microscope; but I think this unnecessary, because one can easily imagine what a worm is like that retains the same figure when it is ten times larger.

Other publications

While the Royal Society did not publish this letter in Philosophical Transactions, it was extracted twice in foreign journals, as were all the letters in Vervolg der Brieven, Letters 53 through 60. In the year after it was written, Jean Le Clerk published an excerpt, including four of the eight figures, in Bibliothèque universelle et historique, vol. 9, p. 152-157.

In 1689, Otto Mencke pubished a short extract, without any figures, in Acta eruditorum, vol. 8, pp. 172-173.