The heat traps may consist of metal sheeting, roofing felt or carpet tiles. Reptiles are cold blooded and are attracted to the refugia which radiate warmth from the sun. The traps are checked by approaching them carefully, looking for any animals basking on the upper surface, then lifted to check for animals lurking beneath.
The most productive times for surveying are usually between April and June and September through mid-October, when reptiles are active but the ambient temperatures are not so hot that they do not seek the warmth from the traps. Both adders and common lizards may emerge earlier from hibernation than other species and may be seen basking in early sunshine in February and March.