At the time of his death, the San Francisco Chronicle reported that he was "reckoned among mental giants" and that he was "an authority of world-wide prominence" in many branches of science.

[1] Encouraged by his friends and mentors, Alexander von Humboldt and Karl Ritter, Behr left Bremerhaven on 27 May 1844 bound for Australia to study botany and entomology, in particular insects in the orders Lepidoptera and Coleoptera.

Arriving at Port Adelaide on 12 September 1844, he travelled to the Lutheran settlement at Bethanian and spent 13 months in the colony of South Australia exploring areas around Gawler, Lyndoch, the Barossa Ranges and the Light, Murray and Onkaparinga rivers.

[2] On 9 October 1845, Behr left the colony, the only passenger apart from the captain's wife, on a small boat, the Heerjeboy Rustomjee Patell, heading for Amsterdam via Batavia.

[4] He spent the next two years in Germany and had papers on the insects of the Adelaide area published in Entomologische Zeitung Stettin[5] and on Australian flora in Linnaea: Ein Journal für die Botanik in ihrem ganzen Umfange.

To avoid the young man's becoming more involved, Behr's father arranged for his son to return to Australia, travelling as ship's surgeon to Adelaide via Rio de Janeiro.

He stayed in South Australia for about one year, during which time he met the Victorian Government botanist, Ferdinand von Mueller and William Hillebrand,[4] who was later to publish Flora of the Hawaiian Islands.

[1] He earned a living as a doctor but there were sometimes conflicts, as when he was accused by the Lutheran newspaper of being a Jesuit, resulting in patients leaving him and forcing him to move his practice.