Thomas Jefferson Papers

To Thomas Jefferson from Jonathan N. Havens and Sylvester Dering, 1 November 1791

From Jonathan N. Havens and Sylvester Dering

Shelter Island Novr. 1st: 1791


We have not the honour of a personal acquaintance, but have presumed to adress this Letter to you at the request of Mr. L. Hommedieu of Southold, by whom we have been informed, that it would be very agreeable to you to receive every possible information respecting the hessian fly; that as a member of the agricultural society of Pensylvania you were in a more particular manner desirous of gaining that information; and that, when he saw you at Southold in the month of June last, he had mentioned our names to you in conversing on that subject. By him we have been encouraged to hope, that if we were to transmit to you an account of our observations on that insect, we might possibly drop some useful hint, or say something which might throw further light on so interesting a subject; and were assured, that if we should be particular in describing its various transformations, and in giving a relation of the various times in which it has prevailed in our part of the country, the account would not be the less agreeable. This intended communication has been delayed until this time, to afford an opportunity of making further observations during the last summer, and examining whether the opinions we had heretofore entertained concerning its nature were in any great degree erroneous; and to see whether further discoveries might not be made which would be useful. When it first made its appearance in our part of the country, if we had apprehended that any of our observations on its nature would have ever extended beyond the sphere of our personal acquaintance, we should without doubt have been more diligent in our inquiries; but as all our experiments and observations were then made merely to gratify private curiosity, or to throw light on the subject in common conversation, we did not pay so much attention to it as its importance required. We reside near each other, and are well acquainted with each other’s observations and opinions on this subject, and have united in writing a single letter to avoid a repetition of the same ideas and sentiments.

The hessian fly was first perceived on Shelter Island, and the adjacent parts of Long Island, a little before the harvest of the year eighty six, and in its progress through the country appeared to come from the westward; and in the fall of the same season it was found in great plenty in the green wheat, and did most injury to that which had been most early sown. At this time the nature of the insect, and its varous transformations, were with us very little understood. In the winter following it was currently reported that the fly was to be found in great plenty in the wheat in sheaf; from whence it was concluded that it must have some immediate connection with, or dependence upon the wheat in grain, either for food or for the preservation of its species. This led us into a careful examination of that kind of insect which was affirmed to be the hessian fly; and we found it in the first place to bear a very great resemblance to a book-louse, in shape, agility, and colour; and as it grew larger it appeared gradually to turn brown, and to have wings, but not to undergo any regular transformation; and at last it became a small black fly. We could discover no other insect except this which could be imagined to be the hessian fly; and this we had no doubt might have been easily discovered before if the wheat had been examined: it was sufficiently evident, both from its shape, and every other attending circumstance, that it could have no relation to, or connection with, the insect discovered in the field; and in this opinion we were abundantly confirmed by all our succeeding observations. In the spring of the year eighty seven, the insect in the field, which was the real hessian fly, increased very fast in the green wheat and at the ensuing harvest many fields were almost wholly destroyed; and in the fall of the same season the wheat again suffered as great injury as before, and the harvest of the year eighty eight was cut off almost universally. The kinds of wheat then in use were the red balled, and summer wheat; both of these were equally affected; rye tho’ less affected in general was in many places much injured; and what appeared most singular was, that a piece of summer barley belonging to Mr. Dering, was about that time wholly cut off. After so general a destruction of wheat for two successive harvests rye was in general sown, except in some instances where the bearded wheat had been obtained, and at the ensuing harvest in the year eighty nine the insect appeared to be gone; and in the fall of this year the several kinds of bearded wheat were pretty generally introduced, and the harvest next following, which was in the year ninety, was in general very good, and very few of the insect were to be seen. This gave great encouragement to farmers and induced them to suppose, that the raising of bearded wheat alone without any other precaution, would prove an effectual remedy against the hessian fly; but notwithstanding the use of this, the fly has again increased in the present year so as to be found in great plenty in many places, which we suppose must be occassioned by our sowing our wheat early; a circumstance very necessary to be attended to with us, that the wheat may obtain a good growth before the cold weather, and be less liable to be injured by the winter. In the two years abovementioned, in which the fly proved so generally destructive to wheat, we made a variety of experiments and observations with a view to ascertain its nature, and method of propagation; and have again had an opportunity of renewing our observations with more particular attention since its increase in the present year; and the result of our inquiries is this; that the hessian fly is a species of insect which has no direct dependence upon the wheat in grain, either for food, or in any other manner for its preservation, but is in the winter season a chrysalis, and remains in the field on the green wheat without suffering any apparent injury from frost or snow, and is transformed into a fly as soon as the weather becomes warm enough in the spring. The period of time in which this transformation is made will begin more or less early according as the season may be more or less forward, and generally continues according to our observations about three weeks: in the year eighty seven we observed it to begin about the sixteenth of april, and end about the first of may; and this we think may be considered as the usual time of its commencement and continuance in our climate. The fly disengages itself from the wheat, by boring a small round hole through its brown case, and through the leaf of the wheat just opposite to the place where it is lodged, and comes forth wrapt in a thin white skin, which it soon breaks, and is then at liberty; and this hole is to be seen in the stubble as long as it remains entire. Very soon after the fly comes out, it is prepared to spread itself every where in the field where it has lain during the winter, or to take its flight to more distant places in search of wheat on which to lay its nits or maggots; and it is at this time that it has an opportunity of going on the summer wheat, which would otherwise escape without being injured. The great variety in the time of its first becoming a fly in the spring, produces the like variety in the time of its laying the maggot on the wheat, but this we suppose may be generally placed between the twentieth of april and the tenth of may; and this period of time like the former must necessarily be regulated by the season; and may perhaps be affected by bad weather and unfavourable winds, which may benumb the fly, or prevent it from taking its flight. The maggot is always found between the inside of the lowest part of the leaf, and the outside of the part which forms the stalk or straw, to which it closely adheres, and is generally, as near the root as possible; but to this there are some few exceptions for it is sometimes, tho’ very rarely, to be found a little above some of the upper joints. It appears at first like a very small white nit or egg; and as it grows larger becomes a sluggish, and almost inanimate maggot, or worm, of a white colour, and capable of very little perceivable motion. This is properly the first state or mode of existence with the insect, and is that in which it destroys the wheat; and altho’ it appears at first to resemble a nit or egg, yet we are inclined to suppose that the fly is viviparous, for we never could discover that any transformation took place from a nit to a maggot. In this state the proper and most natural food of the insect is the sap or juice of that kind of green wheat which has the most delicate straw, and next to this may be ranked the several kinds of wheat whose straw is more firm and solid, and last of all rye and barley: some have affirmed that they have been found on oats, but of this we have no certain knowledge. The maggot obtains the juice altogether by suction, and has no means or faculty of corroding or consuming the solid part of the straw, and as it grows larger its whole body indents the straw, and prevents the rise of the sap, and the grain either falls down or perishes before it has grown to be of any considerable height. The size of the maggot when grown, and the time necessary to compleat its growth, depend in a considerable degree on the quantity of nourishment it may obtain from the grain, and the number of them that may happen to be on one straw; and this time according to our observations is somewhere between four and six weeks, and their growth will generally be compleated in the first part of June: but here the several causes of variety before mentioned conspire to render this time so various that some will be transformed into a chrysalis, whilst others are small, and this circumstance has led many skilful observers to suppose that there are two compleat generations of the insect before harvest. As soon as the maggot has obtained its growth it is transformed into a chrysalis of a dark brown colour, this is the second state or mode of existence which the insect assumes, and is that in which it is mostly observed: in this state it is found in the time of harvest, and when the wheat is gathered remains in the stubble until it undergoes its transformation into a fly; excepting those few which are sometimes in the upper joints, these must necessarily be gathered with the wheat and must always go with the straw, because they adhere too closely to it to [be] beaten or threshed off without being destroyed. The time of their continuance in this state appears to be regulated very much by their enjoying that particular degree of heat and moisture, which is most agreeable to their constitution: if they are removed into the house, and kept dry, and in the shade, they continue longer a chrysalis, than if they remain in their natural situation in the field: cold and wet affect them no otherwise than to continue them in the same state, and prevent their transformation into a fly, as long as they remain in that situation; but of heat they can endure but a small degree, beyond that which is natural for them in the summer seasons and will perish on being exposed to the rays of a hot sun, in such manner as to become very dry, and have all their natural moisture exhaled. Those and various other circumstances render it difficult to ascertain with precision the length of time that they continue a chrysalis during the summer season, but we conclude from our observations that it is not less than two months; and may be prolonged to a much longer time by any of the causes before mentioned. The several causes of variety in the time of their continuing in this state, together with the various times in which they are first formed into a chrysalis in the month of June, conspire to render the period of time in which they make their next transformation, much longer than any of the other periods of time in which they make their several transformations: we think it begins in many instances as soon as the twenty fifth of August, and continues in a greater or less degree through the whole month of September, but by far the greater part are without doubt transformed into a fly in the first part of this month. A reflection here naturally arises, that nature appears to have fixt this transformation, to commence with, and continue through, the whole of that season of the year which is most proper for sowing wheat. The fly is the third and last state of the insect, and compleats what we term one generation: it resembles the moscheto in almost every respect, except that it is much smaller, and has a short bill: it never preys upon the wheat and very probably requires no other nourishment than what it may obtain from dew, or moisture: it is of so delicate a texture as to be injured and destroyed by the slightest accident: and soon after it becomes a fly, it again lays the maggot on the wheat sown in the fall; and if this is not sown soon enough so as to be up at the time the fly requires it, the maggot will be in great measure lost, and the species reduced to an inconsiderable number. The length of time in which it naturally continues a fly is very difficult to ascertain, but is without doubt very short. In the fall of the year the maggot generally proves more destructive to wheat than in the spring, and before cold weather is transformed into a chrysalis, in which state it is prepared to remain during the winter, without any apparent injury from frost, snow, or wet, and in the spring again becomes a fly, which compleats two generations of the insect in one year. It is probable that many, reasoning from analogy, will doubt the reality of this transformation into a fly in the fall, and will suppose that there can be but one compleat generation of the insect in one year: but in support of this we will mention one of our experiments; we gathered a number of the chrysalis from the wheat about the middle of last June, and kept them in the house in a dry place, and out of the sun, and where they could not be molested; and a number of these were transformed into a fly between the tenth, and the thirteenth of September; and besides these a number of others gathered from the stubble after harvest, and placed in the same situation, became a fly about the same time: the remainder of those, which were not transformed at that time, still continue in the same state; this we impute to their being too cold and dry to make their transformation. Since the first of September we have examined the stubble as often as once or twice in a week, and have found them to diminish in number, but that there are still some remaining; from whence we conclude that this transformation in the fall will be in some degree partial; and that many of those, which become a chrysalis late in the month of June, will remain in that state for so long time, that the weather will become too cold for them to make their transformation in the fall; and then they must necessarily continue in that state through the winter, until the weather becomes warm enough in the spring. To this we may add, that if we suppose but one generation in a year, it must follow; that the chrysalis which is formed in June will without exception continue through the winter, and be disposed by nature to be transformed into a fly at the same time with the chrysalis formed in the fall; and that the fly which comes out in the spring will live through the whole summer, and become prolific a second time in the same season; but these are consequences which appear improbable, and difficult to reconcile to phænomena. In the course of all our examinations into the nature of the insect, we have taken the most pains to determine these three points; whether it has any connection with the wheat in grain; whether it is a chrysalis in the time of harvest, and remains in that state in the stubble for any considerable time afterwards; and whether it is transformed into a fly in the fall of the year: with respect to the first of these points, we think it may be considered as clearly decided in the negative, that the insect has no dependence upon the wheat in grain, either for food, or as a place in which to deposit any nit or egg for the preservation of the species: and with respect to the two last, we think, there can be no doubt but that they must be considered as decided in the affirmative.

Of all the various methods which have been proposed to the public for preventing the injurious effects of this insect, that of raising the different sorts of bearded wheat has best succeeded. This kind of wheat, having a more solid straw, resists the impressions made by the body of the insect, and in great measure prevents the injury which arises from stopping the rise of the sap; and very possibly there may be some peculiar quality in this sap, which may render it in some measure disagreeable to the constitution of the insect; but experience shews, that even this sort will not succeed, unless it be attended with the circumstance of being sowed late. Whether any preference ought to be given to any one of the different sorts which have a more firm and solid straw, we have had, during the last year, an opportunity of making one fair experiment; in a field belonging to one of us, were sown three different sorts of wheat, contiguous to each other, and all at the same time; the white bearded; the yellow bearded; and the great red balled, or red-chaff wheat; of these three sorts, the red-chaff was by far the most injured; and the yellow bearded, which lay adjoining to it, least of all.

We will here take the liberty of suggesting a method of destroying them, which has frequently occured to our minds, and which we have not heard mentioned by others; and that is to destroy the stubble of grain soon after harvest. This idea naturally occured on discovering that the insect is then a chrysalis and remains so for some time afterwards. Whether this would be best affected by burning or other wise; and whether the wheat in this case ought not to be cut with the sickle, rather than mowed or cradled; whether the cost that would attend it would not overbalance the advantage; and whether the aid of government might not be necessary to render it uniform and general, are points to be taken into consideration in determining whether any thing of this kind would be feasible, and which we shall not now pretend to discuss: but if the stubble of wheat were to be universally burnt, turned over with the plough, or other wise destroyed soon after harvest, and this were to be done for several years together; we have little doubt in our minds but that it would prove an effectual means of destroying the species: for it is not very probable that the species would be continued long on rye, more especially, as that can be sown much later than wheat without injury from the winter; and the stubble of rye might, if necessary, be as easily destroyed as that of wheat: and if in aid of this, the best sort of bearded wheat were to be used, and that to be sown as late as possible consistent with a good crop, it would be still more likely to succeed.

It has been a received opinion in the country, that they will stay only three years in a place and then be gone; but experience shows that this cannot be true, and we can see no reason why the species should not continue as long as it can find proper food for subsistence. With respect to the probability of their being imported from any foreign country we shall make only one remark, that by our experiments in the last summer it appears, that they may be removed from their natural situation in the field, and be kept alive long enough to be carried across the Atlantic; from which circumstance it appears possible that they might have been imported in straw or stubble. It has been generally remarked, that in spreading over the country, they go between twenty and thirty miles in a year, but as they are a fly twice in the same season, it appears probable, that the fly itself never goes much farther than twelve or fifteen miles. All abstract reasoning and theory on subjects of this nature ought no doubt to be consistent with phænomena, and yield to the test of experiment; if therefore it should appear evident from the experiments and observation of others, that we are wrong in our opinions concerning the nature of this insect, we shall with pleasure stand corrected. A great many particulars respecting our experiments, and the various appearances of the insect, might have been mentioned; but to have given a particular detail of these, would have exceeded the intended bounds of this letter. We are with the greatest respect your most obedient humble Servants,

Jonathan N. Havens

Sylvester Dering

RC (DLC); recorded in SJL as received 1 Dec. 1791. Signed but undated covering letter reads: “Sir, Enclosed we have the honour of presenting you an account of the hessian fly. We reside at Shelter Island in the county of Suffolk, and State of New York, about six miles from Mr. L’hommedieu’s. With the greatest respect we are yours &c.” (RC in DLC: TJ Papers, 67: 11707; franked; endorsed: “Recd. and forwarded by Sir your mo. obedt. Servt., David Gelston”).

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