or cold temperatures disrupt normal behavior. All cimicids harbour bacterial symbionts in paired structures known as "mycetomes". Although the significance of these has not been fully studied, they may be concerned with the biosynthesis of nutrients that the insect cannot synthesize itself, as is the case in other blood-sucking insects. Many cimicids can go without food for long periods, one and a half years in some instances. This allows them to survive the winter at summer bat roosts even when the bats are hibernating elsewhere, and may be an important adaptive trait because of their limited dispersal ability. Cimicids have occasionally been observed clinging to the fore limbs of bats away from the roost, and this is likely to be the means by which the insects disperse. The cimicids have no special adaptations to enable them to travel in this way, however the only two members of the Primicimicinae subfamily, Bucimex chilensis and Primicimex cavernis have claws and an erect a row of peg-like spines on the tarsus, and have been observed clinging to the bat's pelage with these. Hosts Cimicids are a specialised group of blood-sucking parasites that primarily feed on bats, birds and humans. They are thought to have evolved from predatory heteropteran ancestors, with about 60% of extant species using bats as their primary hosts. Bats are social mammals and many species congregate in communal roosts to give birth and rear their young. These roosts provide excellent conditions for their arthropod ectoparasites, with a steady temperature and opportunities for regular blood meals. However, the bats frequently groom themselves and each other, putting the parasites at risk of being eaten. Cimicids lessen this risk by hiding in concealed locations between feeding bouts, and by producing a repellent substance which makes them distasteful. In evolutionary terms, most species of cimicid probably specialised on insectivorous bats or birds, with the possibility of dispersal to other sites via their winged hosts. On returning to a roost, a bat may only be available to cimicids for a short time before it cools down and enters a state of torpor, with reduced blood flow. When the bats lived in close proximity to humans, in caves or in the roofs of their huts, a new opportunity arose; the cimicids could make use of the large size and homeothermic properties of a human, which provided an abundant food supply that led to the growth and