Animals use diverse exogenous materials for constructing their nests, many of them taken from plants. Use of leaf pulp, however, is unique to some species of Osmia and Hoplitis bees. They generate pulp to partition, cap, and in some cases, line their nest cells. I will show how they mince and transport this “pesto”. Cafeteria experiments with nesting Osmia bruneri revealed their ranked preference among 30 leaf species during 2900 leaf visits. Some foliar traits are shown to underpin their choices (e.g. hairiness, kinds of hairs, juiciness, thickness etc). Further insights come from their responses to a soybean isoline for leaf hairiness and variation in leaf sliceability quantified in a mechanical engineer lab. The results have proven predictive in an open garden setting.
