Daphnia ambigua is the smallest Daphnia species, rarely exceeding 1 mm in body length. Its small size makes it especially vulnerable to predation by Chaoborus larvae. In response to Chaoborus kairomones, D. ambigua often forms a sharp pointed helmet on the central axis of the head, typically seen in mid to late summer. Curiously, D. ambigua is often found in cool deep water in the lower thermocline, suggesting a tolerance to cold temperatures, but on the other hand it is one of the most common Daphnia species found in tropical and sub tropical regions.