The neglected impact of tracking devices on terrestrial arthropods

Tracking devices have become small enough to be widely applied to arthropods to study their movement. However, possible side effects of these devices on arthropod performance and behaviour are rarely considered. We performed a systematic review of 173 papers about research in which tracking devices-radio frequency identification (RFID), harmonic radar and radio telemetry tags-were attached to terrestrial arthropods. The impact of such tags was quantified in only 12% of the papers, while in 40% the potential impact was completely disregarded. Often-cited rules of thumb for determining appropriate tag weight had either no empirical basis or were misconstrued. Several properties of a tracking device (e.g. weight, balance, size, drag) can affect different aspects of an arthropod's life history (e.g. energy, movement, foraging, mating). The impact can differ among species and environments. Taken together, these tag effects can influence the reliability of obtained movement data and conclusions drawn from them. We argue that the impact of tracking devices on arthropods should be quantified for each (a) study species, (b) tag type, and (c) environmental context. As an example, we include a low-effort impact study of the effect of an RFID tag on a digger wasp. Technological advancements enable studying the movement of arthropods in unprecedented detail. However, we should adopt a more critical attitude towards the use of tracking devices on terrestrial arthropods. The benefits of tracking devices should be balanced against their potential side effects on arthropods and on the reliability of the resulting data.