In 1799, he accepted a post as surgeon on the vessel
China, a merchant vessel that was to sail to
Java. He passed through
Batavia and was struck by the beauty of the region. In 1801, he applied to be a surgeon with the Dutch Colonial Army in Batavia. Taking up appointment there, he took an interest in the flora, fauna, and geology of the region. In particular, he studied the botany and the insects of the region. One of the first of many species to named after him was the butterfly,
Taenaris horsfieldii. The
East India Company took control of the island from the Dutch in 1811, and Horsfield began to collect natural history specimens on behalf of the governor and friend Sir
Thomas Stamford Raffles. In 1816, Java was restored to the Dutch and Horsfield moved west to Sumatra. In 1819, he was forced to leave the island due to ill health, and returned to London on board the
Lady Raffles. ==England==