While foraging, it is critical for a predator to detect and recognize its prey quickly in order to optimize its energy investment. In response, prey can use low-cost energy strategies such as crypsis and immobility that operate early in the detection–attack sequence. Mesopredators, such as spiders, are themselves attacked by visually oriented predators such as mud-dauber wasps. However, it is not known which colour cues are used by wasps to detect and capture their spider prey or whether there are biases towards such cues. In this study, we evaluated the prey colour biases of two mud-dauber wasps (Trypoxylon tridentatum and Trypoxylon bridwelli) using full-spectrum digital photography and visual modelling. We compared the colour contrast of spiders that were preyed upon with that of the spiders in the surrounding habitat. We show that the spiders captured by the wasps had higher chromatic contrast with their typical backgrounds compared with other co-occurring spider species not found in Trypoxylon nests. Our results suggest that Trypoxylon wasps may exhibit colour biases and/or preferences when hunting their spider prey. Our study highlights the importance of considering the perceptual abilities and biases of predators when studying predator–prey interactions. •We evaluated mud-dauber wasps' colour biases for spider prey.•Araneophagic wasp species showed distinct preferences when foraging for spiders.•Spiders with higher colour contrast with the background were captured more often.•Wasps may use chromatic cues at different stages during detection and attack.