The thermal sense of blood-sucking insects: why physics matters

•The heat released by warm-blooded vertebrates is a major cue for host location.•Molecular receptors react to temperature; behaviour to exchange of thermal energy.•Different physical mechanisms are exploited by different blood-sucking species.•The information provided by thermal perception about a host varies across species.•Heat can modulate other modalities or act as a self-sufficient orienting cue. Blood-sucking arthropods exploit multimodal information for locating and recognising potential hosts. The heat emitted by the body of endothermic vertebrates constitutes a major cue for orientation. To exploit it in a reliable way, insects must be able to deal with two variants of thermal information, that is heat exchange and temperature fluctuations. Evaluating whether or not an object qualifies as a host by its temperature requires solving thermodynamic ambiguities in a context where temperature increase at the receptor level is just one, yet insufficient, piece of information. To be exploitable, this piece of information needs to be integrated with other variables. Here, I discuss the physical constraints associated to thermal orientation, as well as the way different blood-sucking insects acquire and make use of heat to recognise a host.