Building extended phenotypes using incomplete environmental information compromises their design and efficiency.

Animals often face high uncertainty regarding their environment, which might lead to behavioral decisions based on incomplete information. The consequences of using incomplete information are likely exacerbated for animals with “sessile” extended phenotypes (nests, webs, traps). However, such consequences or their fitness implications remain largely unexplored. We examined how incomplete information about soil properties impacts the design and prey capture efficiency of conical pit traps in a sit-and-wait predator, the antlion larvae Myrmeleon crudelis. We experimentally found that (1) Larvae constructed traps with steeper angles of repose than expected for the sand substrate, suggesting that they can manipulate the soil to enhance the trap’s efficiency. (2) When presented with two different soils (all fine-grain vs fine-grain top and coarse-grain bottom), larvae built a pit trap in either one, suggesting that they do not integrate the soil profiles during building. (3) Building traps in suboptimal coarse-grain soil affected the pit trap design, reduced prey capture, and triggered pit trap relocation. Hence, our findings demonstrate that the efficiency of animals' extended phenotypes is reduced when their location is decided based on incomplete information and illustrate how they can cope with the consequences of using sub-optimal structures for prey capture.