Biology of the European beewolf (Philanthus triangulum, Hymenoptera, Crabronidae)

The European beewolf is a solitary digger wasp of the genus Philanthus that comprises about 140 species worldwide. Female beewolves construct nest burrows in sandy soil, hunt honeybees (Apis mellifera), paralyze them by stinging and carry the prey to the nest in flight. One to five honeybees are provisioned as larval food in each brood cell. The larva feeds on the prey and spins a cocoon that is attached with its basal part to the wall of the brood cell. Larvae mostly overwinter and emerge next summer.

Since the conditions in the brood cell are humid and warm, there is a continuous threat that pathogenic microorganisms, in particular mold fungi, infest the larva or the provisioned honeybees, which usually results in the death of the larva. Therefore, there is a high selection pressure on female beewolves to protect their offspring against pathogens, and beewolves evolved at least two different ways to reduce offspring mortality in the brood cell:

(1) They apply large amounts of a secretion from a cephalic gland to the provisioned honeybees, which significantly delays fungal growth on the bees.

(2) The beewolf female secretes a whitish subtance from its specialized antennal glands to the brood cell that contains symbiotic bacteria of the genus Streptomyces. The bacteria are later taken up by the larva and applied to its cocoon, where they significantly reduce fungal infestation and thereby protect the larva.

(3) Beewolf eggs emit gaseous nitric oxide (NO) to fumigate their brood cell. NO is spontaneously oxidized to NO2 with the latter causing a pungent smell of the brood cells. Both are radicals and more or less toxic. As a consequence, most fungi in the brood cell are killed. Thus the paralyzed bees can be consumed by the larva without competition by mold fungi. However, it is a puzzle how the eggs themselves but also the symbiotic Streptoymces bacteria can survive the toxic atmosphere in the brood cell.

Male beewolves establish territories consisting of about 0.25 m2 of vegetation, mostly in the vicinity of the females’ nest aggregations. They mark their territories with a pheromone from cephalic glands and defend them against intruding males in combat flights without physical contact of the opponents. Territories of different males are often found close together, thereby constituting a lek situation in which the females have an ideal opportunity to choose among males. Since the copulation is not preceded by any kind of visual display, female choice could, at least predominately, be based on information obtained from the male sex pheromone.



Strohm E, Herzner G, Ruther J, Kaltenpoth M, Engl T (2019 in press) eLife 2019;8:e43718. Nitric oxide radicals are emitted by wasp eggs to kill mold fungi. DOI:

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Beewolf egg in the brood cell.
Beewolf larva spinning its cocoon in the brood cell.
Female beewolf emerging from the cocoon.
Beewolf female with paralyzed honeybee.
Male and female in copula.

Fotos © Martin Kaltenpoth