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Hessian Fly

When Thomas Jefferson opened his mail on October 22, 1791, he found a small packet of dried stubble from the wheat fields of Long Island. Inside, according to the accompanying letter, was a thriving population of the most infamous insect of the 1790s. Hessian flies [1] had arrived at 274 Market Street, well ahead of the rest of their tribe, still working their way south through the farms of New Jersey.

This was not Jefferson's first encounter with the diminutive enemy of wheat. He had examined some "in the worm state" along the Hudson River the previous May, and throughout the rest of his month-long tour of New York and New England he questioned farmers, tavernkeepers, and roadside blacksmiths about their experiences of the winged pest. Jefferson had taken to the field in his role as chairman of a new committee of the American Philosophical Society, charged with the mission of collecting materials "for forming the natural history of the Hessian fly" and finding "the best means of preventing or destroying it."

The adult Hessian fly is a delicate and harmless member of the gall midge family, in the Order Diptera. Its larval form, however, attacked wheat with such voracity that the appearance of the insect was considered by some American preachers a divine judgment for political sins. The effect of its destruction was captured in an article in the American Museum in 1787: "It is well known that all the crops of wheat in all the land over which it has extended have fallen before it, and that the farmers beyond it dread its approach; the prospect is, that unless means are discovered to prevent its progress, the whole continent will be overrun--a calamity more to be dreaded than the ravages of war."

In the spring of 1791 Jefferson had decided to take an active part in repelling the invaders, first by creating a committee and then by setting out to survey the site of the Hessian fly's earliest depredations. He travelled the entire length of Long Island, eventually reaching the very spot (now under Brooklyn) where American farmers had first watched their wheat stalks shrivel and break in 1777.

In the first years of its ravages, the insect was viewed as an immigrant, a stowaway in the straw for the Hessian troops who disembarked at Flatbush in 1776. George Morgan of Princeton claimed the honor of providing the sobriquet "Hessian." Linking the marauding midge to the German mercenaries provided, he thought, a "useful National Prejudice."

By the 1790s, however, students of the subject were beginning to absolve the Germans of responsibility. Richard Peters declared that "the appellation was bestowed during our revolutionary excitements, when every thing we disliked we termed Hessian." And Dr. Samuel Mitchill, a Long Islander himself, attributed the name to the country people, "ever fond of ascribing every thing disagreeable to the Germans." This professor of agriculture and natural history at Columbia College, after consulting European scholars and scientific works, believed that the fly was an American native.

Jefferson, who heard Mitchill's "Short Memoir on the Wheat-Insect" read at an August 1791 meeting of the Philosophical Society, came to the same conclusion in 1792. Back in 1791, when transmitting news of the Hessian fly committee to Thomas Mann Randolph, he had recommended that his son-in-law take up the study of the resident southern wheat pest, the grain weevil. Contemplating such an activity from a desk cluttered with letters of vice-consuls and notes on national debts, Jefferson was moved to lament, "I long to be free for pursuits of this kind instead of the detestable ones in which I am now labouring without pleasure to myself, or profit to others."

His chance came in June of 1792, when he was given a second batch of pupating Hessian flies (the fate of the first is unknown). For two weeks he watched over the flaxseed-like chrysalises, was present at their "hatching," observed an adult fly laying her eggs, and recorded details of a minute anatomy--presumably with the aid of a microscope, as the fly was "between the size of a gnat & musketoe." He recorded the eight saffron-colored "annuli" on its abdomen, its two "moniliform" antennae, and two "balances like the plectrum of the sticcada," a keyed instrument he had seen Benjamin Franklin play in France.

Certainly at hand were his zoological reference works, since he wrote to Randolph on June 15, "The examination of a single one which hatched a week ago, gives me reason to suspect they are non-descript, and consequently aboriginal here." When the Hessian fly finally received a scientific name in 1817, its describer, Thomas Say, also believed it indigenous to North America. Modern efforts to determine its nationality have resulted in disagreement (most favor Europe, some Asia), but all authorities now concur that Mayetolia destructor is an introduced species.

Since April 1791, when he had moved for the formation of the select committee on the Hessian fly, Jefferson had looked like the answer to Samuel Mitchill's call for a hero to defend American crops. "We are almost entirely in the dark respecting the history of the insects injurious to our useful plants," the learned doctor told a meeting of the Agricultural Society of New York in January 1792, "and that man would be laudably and beneficially employed, who should collect what is knowable concerning the different moths, bugs, flies and worms, which infest our fields and gardens."

That man was not to be Thomas Jefferson. Jefferson had made avid investigations on the fly's breeding grounds, had been an active committee chairman, and had made his own brief foray into entomology--but nothing followed. This is particularly puzzling because throughout 1792 responses were trickling in to the committee's widely published questionnaire about the wheat pest. These answers still lie unpublished in the chairman's papers. Jefferson seems never to have made his own conclusions known and his committee published no final report. He turned instead to combatting an infestation of Hamiltonian notions and the Hessian fly continued its southward progress.

It was observed "crossing the Delaware like a cloud." In 1797 it invaded the fields of Mount Vernon. In 1801 it was "laying waste" all the wheat near Washington. And in June 1803 Jefferson received specimens of the fly "in three stages" from his son-in-law John Wayles Eppes in Chesterfield County, Virginia. "I have examined your Hessian flies and find them very genuine," he replied from the President's House, "on which I condole with you."

His own fields at Monticello seem not to have been affected until 1811, after which there were bad years and worse. He lost one third of the wheat crop to the fly in 1813 and in 1817 was provoked to write: "We, of this state, must make bread, and be contented with so much of that as a miserable insect will leave us. This remnant will scarcely feed us the present year, for such swarms of the Wheat fly were never before seen in this country." Jefferson may then have wished that increasing social duties and the barbs of Hamilton had not distracted him from completing his fly research. Other factors had probably contributed to his retirement from the cause. The cyclical pattern of the Hessian fly's assaults caused some observers to believe it was on the decline in 1792. He may also have felt that some articles published in that year sufficiently cleared the good name of American wheat, by demonstrating that the fly never infested the grain. He had been incensed by a British Order in Council in 1788 prohibiting importation of American wheat which, it was feared, might harbor the new pest. Although Jefferson had no interest in sustaining Englishmen with American produce, he dreaded the effects of the British action on trade with nations he favored. "It is a mere assassination," he declared, a libel founded on faulty information.

It is just as well that the bug committee was dormant during Jefferson's presidential years. Federalist journalists had enough fun with the "bone committee" of the [[American Philosophical Society]], considered a hotbed of Jeffersonians. The sight of politicians peering into the secrets of nature offended Jefferson's opponents. "Science and government are two different paths," observed one author. "He that walks in one, becomes, at every step, less qualified to walk with steadfastness or vigour in the other." Honored for his breadth of vision by his friends, Jefferson was convicted by the Federalists for his curiosity. The philosopher-president was viewed as an irresponsible visionary, subject to "philosophic fogs."

Federalist satirists found the minute examinations of natural history particularly worthy of ridicule, and made Jefferson's study and measurement of fossils a frequent target. Fourteen-year-old William Cullen Bryant dismissed his chief of state with the rhyme:

Go search, with curious eye, for horned frogs,

'Mongst the wild wastes of Louisianan bogs;

Or, where Ohio rolls his turbid stream,

Dig for huge bones, thy glory and thy theme.

Jefferson's reputation as an observer of insects was not forgotten, at least by Washington banker John P. Van Ness, who in 1806 sent to the President's House two worms just plucked from his Lombardy poplar tree. Wondering if this might be the poisonous "reptile" lately exciting comment, Van Ness supposed that it would be "gratifying" to Jefferson "to observe the worm particularly."

Whether the Federalist journalists had any idea of the president's interest in insects, they could not resist portraying him in an entomological mode. Joseph Dennie, whose Port Folio adopted Jefferson as "our political Mammoth," published a supposed fragment of his diary, found on the banks of the Potomac. In it, Jefferson suffers writer's block after irritating public business interrupts his composition of a "dissertation on cockroaches." In 1807, a youthful Washington Irving created a fictional Tripolitan tourist, who hears that the president is "a very plain old gentleman--something they say of a humorist, as he amuses himself with impaling butterflies and pickling tadpoles."

Jefferson's amusement at the schoolboy satire of the opposition party was no doubt faint, but if he did not collect butterflies he did make a scrapbook of the poems, squibs, and caricatures of the Federalist press. His vexation surfaced later when he wrote that his opponents saw "even science itself as well as my affection for it as a fit object of ridicule and a disqualification for the affairs of government."

The explosion of the Hessian fly population in 1817 brought forth another burst of publications. Thomas Say gave it a proper scientific description and name in the journal of the Academy of Natural Sciences. John Hartwell Cocke of Bremo, in the American Farmer, described for the first time the hatching of its egg. Samuel Mitchill returned to the subject in the American Journal of Science, and his brother-in-law Samuel Akerly opened his own article with a reference to the greater scope offered to all manner of insects by the new immensity of the agricultural nation. He also recommended changing the fly's name, which had been "saddled upon the poor Hessians, who are innocent of the charge."

Akerly closed by reviewing the commonly used methods for evading the worst injuries of the insect: sowing late in the fall; using bearded wheat; manuring well; and ploughing in or burning the stubble after harvest. Jefferson's own optimistic view in 1792 had been that "a particularly vigorous species of bearded wheat and good husbandry seem to he a perfect preservative." In 1803 he still advocated manuring well and sowing the yellow bearded wheat, and actually considered the Hessian fly "a great blessing" because it drove American farmers to adopt improved agricultural habits.

As for sowing later in the fall, he once declared it "a poor remedy," but seems to have been forced to adopt it by 1814, when he recorded in his Farm Book the proper seeding time as October 10 to November 10. "What is sown either earlier or later is subject to the fly." Interestingly, the current "fly-safe" sowing date for Albemarle County is October 9. The Hessian fly, who now lives wherever wheat is grown in the United States, is kept in check by the very techniques practiced by the observing farmers of Jefferson's time: late planting, fertilizing, and cleaning the fields after harvest. And the search still goes on for a resistant wheat species.

In 1818, twenty-five years after Chairman Jefferson had gathered in letters and questionnaires, the findings of the [[American Philosophical Society]] committee on the Hessian fly were finally made public. Jefferson's son-in-law Thomas Mann Randolph read before the Agricultural Society of Albemarle "An Historical and Physiological Notice of the Hessian Fly" (published in 1825 in the American Farmer). Randolph summarized in turn the observations of each correspondent, whose reports had lain so long undisturbed in one of the cartons in Jefferson's cabinet. He concluded with the recent observations of General Cocke, whom he credited with being "the first to discover the locomotive power of the young caterpillar."

Federalists were forgotten and entomological investigations left to others when Jefferson contemplated the cosmos in 1823. To John Adams he wrote: "It is impossible for the human mind not to perceive and feel a conviction of design, consummate skill, and indefinite power in every atom." He knew what he was talking about when he itemized the movements of celestial objects, the structure of the earth, animals and plants "examined in all their minutest particles," and "insects mere atoms of life, yet as perfectly organised as a man or mammoth."

Primary Source References

1787 April 26. (William Hay to Jefferson). "The Farmer however has seen with sorrow his Crops of small grain, particularly the wheat and frequently the Corn almost totally destroyed, for some years past, by a pernicious Insect. The Damage is done, while it is yet in its first Stage of existence; the little Enemy dwells in safety between the outer Leaves which cover the Joints, and the Stalk. In this state they appear not unlike a young Bed Bug and smell exactly as they do, they differ in Colour only by a duskish black Streak across the Neck; when they have acquired wings, they are all over of that dusky Colour, except a very large one which you will find now and then of the same Colour of the Young Brood, whether Male of Female I have not been able to determine. No remedy has been found out for them. Their Progress is from South to North, and such Havock have they made, that Many Farmers have been obliged to leave off the Culture of wheat, and by that Means, they have left their Farms. The same Bug is known to the Northward and is there denominated the Hessian Fly."[2]

1788 July 24. (James Madison to Jefferson). "Crops in Virginia of all sorts were very prromising when I left the State. This was the case also generally throughout the States I passed thro' with local exceptions produced in the Wheat fields by a destructive insect which goes under the name of the Hessian fly. It made its first appearance several years ago on Long Island, from which it has spread over half this State [New York], and a great part of New Jersey; and seems to be making an annual progress in every direction."[3]

1789 February 16. (Thomas Paine to Jefferson). "A Paper from the Privy Council respecting the American fly is before Parliament. I had some conversation with Sir Joseph Banks upon this subject as he was the person whom the privy Council referred to. I told him that the Hessian fly attacked only the green plant, and did not exist in the dry grain. He said that with respect to the Hessian fly they had no apprehension, but it was the Wevil they alluded to..."[4]

1789 May 17. (Jefferson to Benjamin Vaughn). "Your nation is very far from the liberality that treaty inculcates. The proposed regulation on the subject of our wheat is one proof. The prohibition of it in England would of itself be of no great moment, because I do not know that it is much sent there. But it is the publishing a libel on our wheat sanctioned with the name of parliament, and which can have no object but to do us injury by spreading a groundless alarm in those countries of Europe where our wheat is constantly and kindly received. It is a mere assassination. If the insect they pretend to fear be the Hessian fly, it never existed in the grain."[5]

1791 April 2. (Jefferson to Charles Thomson). "The Philosophical society have appointed a committee, of which you are named, to collect materials for forming the natural history of the Hessian fly, the best means of preventing or destroying it &c. This committee meets tomorrow. I therefore send the bearer express, in hpes you will find it convenient to come..."[6]

1791 May 1. (Jefferson to Thomas Mann Randolph). "A committee of the Philosophical Society is charted with collecting materials for the natural history of the Hessian fly."[7]

1791 May 12. (Jefferson to Benjamin S. Barton and others). "TH:Jefferson presents his respects tot he gentlemen of the committee on the Hessian fly, and prays their attendance at the Hall of the Philosophical society tomorrow (Friday) at half after seven P.M....He leaves town on Sunday for a month, to set out on a journey which wil carry him through N. York and the whole of Long island, where this animal has raged much. He is therefor anxious to take with him the decision of the committee and particularly prays of Dr. Barton to have his queries prepared to present to them."[8]

1791 June 21. (Jefferson to James Madison). "I will thank you if in your journey Northward you will continue the enquiries relative to the Hessian fly, and note them."[9]

1791 September 10. (Ezra L'Hommedieu to Jefferson). "Since I saw you at this Place I have received from Colo Sylvester Dearing of Shelter Island some Observations he had made on the wheat Insect commonly called the hessian fly, which I send you herewith inclosed with some Stubble of the yellow bearded wheat...By carefully examining this Stubble, by opening the Straw near the Roots and first Joints you will find many of the Insects in their chrysolis State still alive and their Inclosure or Case very Tender. This Stubble was taken from the field in the beginning of Harvest..."[10]

1791 December 22. (Jefferson to Havens and Dering). "I return your thanks for your letter of Nov. 1. with the valuable information it contained on the subject of the Hessian fly. They throw peculiar light on the generations of that insect, which other information had placed under much confusion. If further observations should confirm the fact that there are but two generations a year, it may lead perhaps to a remedy. As the Committee of the Philosophical society will probably continue their enquiries thro' another year, any further observations which you may make will be thankfully received and communicated..."[11]

1792 June 3. (Jefferson to Daniel L. Hylton). "The Hessian fly is very mischievous around this city and considerably Shouthward, even into Maryland as is said. It has certainly made a great stride Southward this year."[12]

1792 June 15. (Jefferson to Thomas Mann Randolph). "The Hessian fly has made an alarming progress to the Southward this year. They talk of them at Baltimore. This neighborhood abounds with them. A particularly vigorous species of bearded wheat and good husbandry seem to be a perfect preservative against them. We have an opportunity now of examining this insect well. I have several of them now hatching. The examination of a single one which hatched a week ago, gives me reason to suspect they are non-descript, and consequently aboriginal here."[13]

1792 June 20. (David Redick to Jefferson). "I find by a late news paper that the Philosophical Society wishes to learn among many other things respecting the Hessian Fly wheather their progress have been Stoped [sic] by mountains as also the course they Steer. I can Now inform the committee that the fly appears this Season about Six or Sven Miles South of this Town [Washington]. Several fields of wheat are much injured."[14]

1792 July 16. (Joseph Moore to Jefferson). "I have taken this Opportunity to transmit to you Answers to some of the questions proposed by the Committee of the Phylosophical society, with regard to the Hessian Fly..."[15]

1792 October 6. (John Sheppart ot the Committee). "I receiv'd through your Casper Wistar a Request to Communicate what Accrued to my Observation in regard to the Hessian fly...'[16]

1792 October 12. (James Mease to Jefferson). "That the insect did not confine itself to the lower joint, but had in may instances invaded the second and nested in considerable numbers without the sheath of it. In one case I saw the worms on the head, among the aristae of bearded wheat, but this was a case where the spike had scarcely protruded beyond the investing foliage. My friend can justly claim the honor of the discovery, from all I have heard, of the fly being an entire American production..."[17]

1793 June 13. (Jefferson to Gouverneur Morris). "The Hessian fly, however, to the north, and the weavil to the south of the Potomac, will probably abridge the quantity (of small grain crops)."[18]

1801 November 16. (Jefferson to Thomas Mann Randolph). "The Hessian fly is laying waste all the wheat in this quarter, the late as well as early sown."[19]

1803 June 14. (John Wayles Eppes to Jefferson). "We have got the Hessian Fly I believe in our Wheat--I have lost I image 1/3 of my crop here-I enclose you a specimen of the Fly in three stages and will thank you to examine them and inform me whether you suppose it to be the real Hessian Fly--P.S. the crops in Charles city are entirely destroyed with the Fly."[20]

1803 June 19. (Jefferson to John Wayles Eppes). "I have examined your Hessian flies and find them very genuine, on which I condole with you. A poor remedy is sowing so late as to die by the rust. The advantageous remedy is to sow no more wheat grounds than can be well manured, and sowing the yellow bearded wheat, the surplus grounds put into rye and clover. They attack barley more readily than wheat. When they drive us to this, they are a great blessing."[21]

1803 October 10. (Jefferson to Richard Bailey). "I received lately from France a few grains of a wheat with a solid stem. As from this circumstance it will probably be proof against the Hessian fly, I an dividing it among those whoe I think will take care of it. I send you a few seeds."[22]

1807 November 16. (Jefferson to Thomas Mann Randolph). "The destruction of wheat by the Hessian fly is general through the states."[23]

1807 November 21. (Jefferson to James Maury). "The wheat sown for the ensuing year is in a great maesure destroyed by the drought and the fly."[24]

1811 May 5. (Jefferson to James Monroe). "The Hessian fly appears alarmingly in our growing crops."[25]

1811 June 10. (Jefferson to Charles Bankhead). "Altho' we have lately had very seasonable rains, the wheat does not get over the injury of the fly. The crop will be light except in the tobacco grounds and other very rich lands."[26]

1811 July 13. ((Jefferson to James Madison). "We are at the close of the poorest harvest I have ever seen. I shall not carry into my barn more than one-third of an ordinary crop...much of the evil had been prepared by the winter and the fly."[27]

1811 July 21. (Joel Barlow to Jefferson). "Mammoth Rye. I received it last year from France...The stalk being more solid than that of common rye it will probably resist the fly."[28]

1813 May 21. (Jefferson to James Madison). "We have never seen so unpromising crop of wheat as that now growing. The winter killed an unusual proportion of it, and the fly is destroying the remainder. We may estimate the latter of loss at one-third at present, and fast increasing from the effect of the extraordinary drought."[29]

1814 May 3. "The period for sowing wheat is from October 10. to Nov. 10. What is sown either earlier or later is subject to the fly."[30]

1817 May 10. (Jefferson to William Johnson). "We, of this state, must make bread, and be contented with so much of that as a miserable insect will leave us. This remnant will scarcely feed us the present year, for such swarms of the Wheat-fly were never before seen in this country."[31]

1817 July 16. (John Love to Jefferson). "He [Monroe] was then satisfyed from the different appearances of the common wheats, and the kind here called the Lawler, that the latter was unjured by the Hessian fly, and engaged from me 200 bush'ls for himself, and 200 for you, to whom he mentioned his intention to write on the subject."[32]

1817 August 3. (Jefferson to John Love). "I have heard much of it's superior security from the fly, and indeed know something of it from an example in my neighborhood. How it may stand in comparison with our red bearded wheat in other important circumstances we do not know, and therefore I have concluded to sow enough of it only to produce my stock of seed for another year."[33]


  1. This article is based on Lucia C. Stanton, Monticello Keepsake, November 1, 1991.
  2. PTJ, 11:319.
  3. Ibid, 13:414.
  4. Ibid, 14:567.
  5. Ibid, 15:133-134.
  6. Ibid, 20:245.
  7. Ibid, 20:341.
  8. Ibid, 20:395.
  9. Ibid, 20:560.
  10. Ibid, 22:139.
  11. Ibid, 22:428.
  12. Ibid, 24:22.
  13. Ibid, 24:83.
  14. Ibid, 24:103.
  15. See the complete letter, Ibid, 24:234-235. Also at the Library of Congress.
  16. See complete letter, Ibid, 24:446-447. Also at the Library of Congress.
  17. Ibid, 24:471.
  18. Ibid, 26:276.
  19. Library of Congress.
  20. University of Virginia.
  21. Ibid.
  22. Betts, Garden Book, 287.
  23. Library of Congress.
  24. Betts, Garden Book, 353.
  25. >PTJ"RS', 3:607.
  26. Ibid, 3:644.
  27. >Betts, Garden Book, 502.
  28. PTJ:RS, 4:49.
  29. >Betts, Garden Book, 511.
  30. Betts, Farm Book, 84.
  31. >Betts, Garden Book, 572.
  32. Ibid, 573.
  33. Ibid, 574.

Further Sources

  • American Philosophical Society's Circular on the Hessian Fly. 17 April 1791. PTJ, 22:430-433.
  • Jefferson's Notes on the Hessian Fly. 24 May-18 June 1791. PTJ, 22: 456-462.
  • Letter from Johnathan N. Havens and Sylvester Dering. 1 November 1791. PTJ, 22:244-253.


GregArrington's picture
This is the species of fly that is a significant pest of cereal crops including wheat, barley etc. It is important to do pest control. For more information about different types of flies visit online.


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