4.3.2 Extraction The advantage of this system is the ease of extraction. The bats are not tangled and can be removed from the collecting bag when required. 4.4 Mist-nets 4.4.1 Description These nets consist of fine nylon or terylene netting, which is usually held in tension between two poles (Figure 4.6). Mist-nets are supplied to responsible licence-holders through the British Trust for Ornithology (BTO), in standard lengths of 6 mm) and 18 m (60'). Loose netting can also be purchased to makeup nets of any length. The height of the nets is divided into ‘shelves’, each with a loose pocket of netting that holds the trapped animals. Nets can have between one and four shelves, but four are most usually used for catching bats. The nets have a mesh size of 13" or, the latter being preferable as it is apparently less easily detected by bats. The main problems with mist-nets are entangling bats, risk of damaging them during extraction and potential predation. Mist-netting should be avoided between mid-June and mid-July because adult females maybe heavily pregnant, lactating orb HARP TRAP 43 carrying youngsters, which may become dislodged. They should not generally be used outside roost entrances, where large numbers of bats are likely to emerge/enter. The use of mist-nets will be licensed only following adequate training insetting of nets and extraction of bats.