Philanthus

Taxonomy

Order: Hymenoptera
Family: Crabronidae
Subfamily: Vespinae
Tribe: Philanthini
Genus: Philanthus Fabricius, 1790
Common names: beewolves, bee-hunters, or bee-killer wasps

Background

Philanthus species are solitary, predatory wasps. The majority of species prey on bees, hence their common name. These wasps build solitary nests in the ground. Adult females provision their nests with insects, like bees, to feed their larvae. The adults consume nectar from flowers.

How to separate from Asian giant hornet

  • Beewolves are generally much smaller than Asian giant hornets, although some species can be around half as long as AGH
  • Their heads appear large for their bodies and their eyes are oval (not notched)
  • Although beewolves can prey on bees, they are solitary and do not form large colonies or nests like AGH

Distribution

There are 31 species of Philanthus in the Nearctic region, with 18 in California. The genus is found worldwide, except in South America where it is replaced by Trachypus (Bohart and Grissell 1974).

Distribution of Philanthus by GBIF: https://www.gbif.org/species/1338932

Diagnostic characteristics

To identify the family (Crabronidae):

  • The pronotum is short and collar-like with a rounded lobe on each side that does not reach the tegula
  • The inner margin of the compound eye smooth and rounded, not notched
  • The gaster is attached to the thorax by a very short petiole

To identify the tribe Philanthini:

  • The apex of the hind femur is simple, without a flattened plate
  • The inner orbit of the eye is sharply angled or notched
  • The episternal sulcus is present and usually reaches the ventral area of mesopleuron

To identify the genus Philanthus:

  • The last antennal segment is rounded apically, with a partly ventral, oval polished spot
  • The first gastral segment usually broader than long
  • Body length 7–18 mm (0.3–0.7 inches)
  • There are only 2 genera in the tribe Philanthini: Philanthus (Old and New World, but not South America), and Trachypus (South America to Brownsville, Texas)

Diversity

There are 140 known species of Philanthus worldwide.

Host/prey associations

Adult beewolves feed on nectar, but the larvae are fed bees and other insects provisioned by females at the time of egg-laying. They prey particularly on sweat bees (family Halictidae), but at least one European species specializes on honey bees (Apis mellifera) (Bohart and Grissell 1974).

Nesting and general behavior

Females hunt for prey on flowers, at solitary bee and wasp nests and apiaries. They excavate tunnels in the ground for their nests. Some species, like P. bilunatus and P. nasalis, nest in sandy, flat locations, while others, like P. gibbosus, build their nests near forest edges, in meadows, or even in cliff faces. The average nest contains 3–7 cells, and each cell can contain 3–18 bees and/or wasps as larval food. Females may share nest entrances, but each female uses its own cells (Bohart and Menke 1976). They sleep in their nests after closing the entrance from the inside.

Males are territorial and use pheromones to mark twigs and other objects in their vicinity to claim the territory from other males. They tend to sleep in aggregations in small tunnels and in the ground.

Adults are present from June to September in North America, and only have one generation per year.

<p><em>Philanthus gibbosus</em>; photo by Christina Butler, Flickr</p>
<p><em>Philanthus</em> sp.; photo by Charlie Jackson, Flickr</p>
<p><em>Philanthus gibbosus</em>; photo by Judy Gallagher, Flickr</p>
<p><em>Philanthus</em> sp.; photo by Frank Vassen, Flickr</p>
<p><em>Philanthus bicinctus</em>, dorsal view; photo by Todd Gilligan, USDA APHIS, PPQ ITP</p>
<p><em>Philanthus ventilabris</em>, lateral view; photo by Todd Gilligan, USDA APHIS, PPQ ITP</p>
<p><em>Philanthus sanbornii</em>, dorsal view; photo by Todd Gilligan, USDA APHIS, PPQ ITP</p>
<p><em>Philanthus bicinctus</em>, lateral view; photo by Todd Gilligan, USDA APHIS, PPQ ITP</p>
<p><em>Philanthus bicinctus</em> (left) compared to <em>Vespa mandarinia</em> (right), dorsal view; photos by Hanna Royals and Todd Gilligan, USDA APHIS, PPQ ITP</p>