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Harmas de Fabre : collections d'insectes du cabinet de travail © MNHN - Agnès Iatzoura

Scientific work

Here are some of the numerous subjects studied by Jean-Henri Fabre, about which the scientist sometimes made discoveries that were ahead of their time.

Ethology and biological struggle

Fabre considered the Harmas to be a paradise for hymenoptera – orders of insects having two pairs of membranous wings, including ants, bees and wasps.

During his work, the entomologist discovered his role as predator on other species and, ahead of his time, laid the foundation for organic agriculture, which uses one species to rid itself of another.

Among the research conducted by Fabre on hymenoptera, his “favourite case” is a study of the care certain burrowing wasps lavish on their offspring. The wasps build reserves of paralysed insects for feeding their larvae. His interest in this “exquisite corpse” was prompted by the work of Léon Dufour, the dean of French entomologists (read the article in Pour la science).

Pheromones

Fabre also took an interest in the reproductive behaviour of butterflies, and in particular that of the Great Peacock Moth.

“The male, equipped with highly developed antennae, is capable of locating a female within a radius of up to ten kilometres.”
During the work he conducted in his study, Fabre observed that a female Great Peacock Moth, born that morning and “forthwith cloister[ed] (...) under a wire-gauze bell-jar,” attracts, in one evening, some forty males “coming from every direction”. Yet when housed in a sealed tin, she attracts no males at all.”

Following these observations, Fabre wonders:

"Are there (...) effluvia similar to what we call odour, effluvia of extreme subtlety, absolutely imperceptible to ourselves [...]? ”

Souvenirs entomologiques, 7th series, p. 374, Paris, Delagrave, 1925.

In this way the naturalist demonstrated the production of a sexual pheromone by the female butterfly, as well as the olfactory role of the antennae.

“It was a memorable evening, this Great Peacock evening [...] the magnificent Moth, largest in Europe, clad in maroon velvet with a necktie of white fur [...] The wings, with their sprinkling of grey and brown [...] have in the centre [...] a great eye with a black pupil and a variegated iris containing successive black, white, chestnut and purple arcs.

No less remarkable is the caterpillar, yellow-hued [...] [whose] robust cocoon [...] is usually found at the foot of old almond-trees. The leaves of the same tree nourish the caterpillar.

Well, on the morning of the 6th of May, a female emerges from her cocoon in my presence, on the table of my insect-laboratory. I forthwith cloister her [...] under a wire-gauze bell jar. [...] I incarcerate her from mere habit... [...] It was a lucky thought. At nine o’clock in the evening , just as the family is going to bed, there is a great stir in the room next to mine. Little Paul [...] is rushing about, jumping and stamping [...] like a mad thing. [...] “Come quick” he screams. “Come and see these Moths, big as birds! The room is full of them!” [...]

We enter the room, candle in hand. What we see is unforgettable. With a soft flick-flack, the great Moths fly around the bell-jar. [...] How many of them are there? [...] Coming from every direction and apprised I know not how, here are forty lovers eager to pay their respects to the marriageable bride born that morning amid the mysteries of my study.”

Souvenirs entomologiques, 7th series, p. 363 / 364 / 365, Paris, Delagrave, 1925.

Grand Paon de nuit © Wikimedia commons

Animal memory

“One would say that the insect possessed something more subtle than mere recollection — a kind of intuition of locality with which nothing in us corresponds — in short, an indefinable faculty which I call memory for lack of any other expression by which to designate it. The unknown cannot be named.”

Souvenirs entomologiques, 1st series, p. 303, Paris, Delagrave, 1925.

“To explain all these mysteries, we necessarily arrive at the notion of another mystery – that is, a special sensibility, denied to human nature. Charles Darwin, whose imposing authority no-one will challenge, arrived at the same conclusion. To determine if the animal is not impressed by telluric currents, seek to find whether it is not influenced by [...] a magnetic sensitivity? [...] I am speaking of the magnetism of physicists [...] and not that of a Messmer or a Cagliostro.”

Fabre thus eventually admitted the existence of “a special sense, so foreign to our own organisation that we can not even imagine it, that directs the pigeon, the swallow, the cat, the chalicodoma and so many others, to foreign lands. Whether that sense is magnetic or not I shall not decide, being satisfied that I have contributed, in no small part, to demonstrating its existence.”

Souvenirs entomologiques, 2nd series, p. 143, Paris, Delagrave, 1925.

Praticien du mesmérisme utilisant le magnétisme animal, Wood engraving, Franz Anton © Wellcomelibrary

Instinct

Based on his observations, the naturalist explains the behaviour of insects by instinct – a kind of internal force inherited from creation. In his view, “Instinct knows everything in the unchanging paths laid out for it; beyond them it is entirely ignorant.”
His research in fact served as point of departure for Bergson’s work on the subject.

“The instinct aroused by a chance act that proves favourable for the animal is an acquired habit. And on that, arguments invoke natural selection, atavism, the struggle for life. I see a good many big words, but I prefer a few small facts. And for forty years before long I have been gathering these little facts, examining them. And they don’t tally exactly with current theories.”

Souvenirs entomologiques, 2nd series, p. 51, Paris, Delagrave, 1925.

“Instinct knows everything in the unchanging paths laid out for it; beyond them it is entirely ignorant. The sublime inspirations of science, the astonishing inconsistencies of stupidity, are both its portion, according as the creature acts under normal conditions or under accidental ones.”

Souvenirs entomologiques, 1st series, p. 208, Paris, Delagrave, 1925.