"before joining them", but also had two more plant books in mind, and a revision of Fertilisation of Orchids to work on. He also began an autobiographical work intended for his family's eyes only. After turning away a request to support a controversial book on contraception (Fruits of Philosophy) – Darwin was opposed to it – he got back to work on flowers and worms. As with much of his geological and evolutionary work, worms were a case of gradual, barely noticeable changes accumulating over time into large effects. He even went on a two-hour excursion to Stonehenge to see how its monoliths had been buried by earthworm castings. He was occupied by worms at Downe in 1880, his work coming first. He had help from the family, even receiving soil samples from Abinger's Roman ruins. He told Vladimir Kovalevsky (his Russian translator) of slow progress with his new book. Darwin calculated that there were 53,767 earthworms recycling away per acre. He carried out experiments indoors, where they worked the earth inside pots in a worm-littered room. He experimented with stimuli at night: strong light would send them into their burrows ("like a rabbit" said Darwin's grandson Bernard), but heat and sound had no effect. Their food preferences were also tested, raw carrots being their favourite. Darwin was fascinated by their behaviour, from enjoying "the pleasure of eating" (based on their eagerness for certain foods) to their sexual passions, "strong enough to overcome... their dread of light", even to their social feelings ("crawling over each other's bodies"). Their foraging was especially intriguing: they dragged leaves into their burrows, pulling them in the most efficient way, by their pointed end. On these semi-intelligent creatures Darwin wrote that they obtained a "notion, however rude, of the shape of an object", perhaps by feeling it out. Worms, "five or six feet" below the ground ploughed farmers fields. Darwin felt we "ought to be grateful" to these little recyclers, which he compared to "a man... born blind and deaf". He was wondering how long it would be until he would be consumed by worms himself. It would surely be his last major work; he told German translator Victor Carus "I have little strength & feel very old". By 1881 he was unable to summon the strength for revisions and handed Worms on to Frank. His health gave him troubles; he complained to his long-time