Ansorge, magistrate and collector in Bihar and Orissa; and an amateur entomologist, he wrote a Report on an Inquiry into the Silk Industry in India (1917) in three volumes but not without a major interruption. While in Bangalore on the silk study, on 17 April 1916, he received a telegram from the government seeking help on fly control in Mesopotamia. Appointed as an acting Lt-Col, he was sent to assist C.F.C. Beeson and shipped out from Bombay. He published on his investigations into the control of flies and other pests, a note in the Agricultural Journal of India included a photograph of his assistants from Pusa. He also introduced a treatment for the control of lice in the trenches called that kept away jigger fleas and ticks. It was reported that there was a fall of 66% in cases of dysentery, cholera and typhoid after his measures were put in place. A bout of beri-beri invalided him and he returned to India, recovered and then travelled to England. Shortly after, there was a problem with weevils infesting wheat in Australia which hampered food supplies during the war. In October 1917 he sailed to San Francisco and then to Sydney where he examined the wheat weevil problem along with W.W. Froggatt, the Government entomologist and suggested various measures. He also examined the issue of sheep blowflies Lucilia sericata before setting off from Sydney to England in May 1919. In 1924, Lefroy and his assistant Elizabeth Eades started producing bottles of woodworm treatment fluid from a small factory in Hatton Garden to manage a stream of requests, this led to the formation by them of a company called Rentokil Limited (now Rentokil Initial) in 1925. He registered the company on 29 September 1924, originally under the name of Entokill but this was objected to by the Board of Trade. Maxwell-Lefroy's students included Evelyn Cheesman who took up a position at the insect house in the zoo from 1919. Maxwell-Lefroy had been appointed honorary curator for the insect house. Cheesman and Olive Lodge also attended his classes which otherwise included only male students. He encouraged their studies and when Cheesman set off for South Africa, he emphasized the need for anyone interested in insects to spend time in the tropics to fully appreciate the subject. In 1922 he began to collaborate with Bruce Woolf who started a film company called New Era films