European beewolf

European beewolf
A European beewolf
European beewolf paralyzing a bee
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Hymenoptera
Family:	Crabronidae
Genus:	Philanthus
Species:	P. triangulum
Binomial name
Philanthus triangulum (Fabricius, 1775)
Synonyms[1]
Philanthus abdelcader Lepeletier, 1845 Philanthus allionii Dahlbom, 1845 Philanthus apivorus Latreille, 1799 Philanthus discolor Panzer, 1799 Philanthus pictus Panzer, 1797 Crabro androgynus Rossi, 1792 Philanthus ruspatrix (Linnaeus, 1767) Simblephilus triangulum (Fabricius, 1775) Sphex scutellatus subsp. maculatus Christ, 1791 Vespa fasciata Fourcroy, 1785 Vespa limbata Olivier, 1792 Vespa ruspatrix Linné, 1767 Vespa triangulum Fabricius, 1775

European beewolf carrying a bee to the nest

Philanthus triangulum, commonly known as the European beewolf, bee-killer wasp or the bee-eating philanthus (from the now obsolete synonym Philanthus apivorus), is a solitary wasp that lives in the Western Palearctic and Afrotropics. Although the adults of the species are herbivores (feeding on nectar and pollen), the species derives its name from the behavior of the inseminated females, who hunt Western honey bees. The female places several of its paralyzed prey together with an egg in a small underground chamber, to serve as food for the wasp larvae. All members of the genus Philanthus hunt various species of bees, but P. triangulum is apparently the only one that specializes in Western honey bees.

Identification

The European beewolf is a spectacular species of solitary wasp with bold yellow and black markings on the abdomen, males have trident-shaped markings between their bluish eyes while the larger females have a reddish stripe behind the eyes and a pale face.^[2]

Habitat

The European beewolf is found mainly in areas of open sandy ground in areas such as lowland heathland and coastal dunes.^[2] They are infrequently found in clay areas and in Britain have been recorded digging burrows in coal dust and ash and have been found on spoil heaps from coal mining.^[3]

Subspecies and distribution

The European beewolf has a wide distribution in the Afrotropical and Western Palearctic zoogeographical regions from Scandinavia to South-Africa.^[3] In Europe the distribution of has been moving northwards as summers have longer periods of warm weather.^[2]

There are currently five recognised subspecies:^[3]

• Philanthus triangulum abdelcader Lepeletier, 1845 northern Africa and the Middle East from Iraq westwards to the Atlantic and the Canary Islands this subspecies also occurs on the Italian island of Lampedusa;
• Philanthus triangulum bimaculatus Magretti, 1908 Kenya;
• Philanthus triangulum diadema (Fabricius 1781) the Afrotopics;
• Philanthus triangulum obliteratus Pic 1917 Algeria and Egypt:
• Philanthus triangulum triangulum (Fabricius, 1775) Europe.

Biology

In the more northerly parts of its distribution the European beewolf is univoltine and the flight period is between mid-July and September. In the warmer area in which it occurs there can be more than one generation per year, for example in central Europe there may be two broods in the summer.^[4]

Female European beewolves excavate their burrows in sandy soil or in vertical soil faces in open sunny places^[2] and these can be up to a metre in length with no less than three and as many as 34 short side tunnels at the end, each of which contains a brood cell. The material displaced by the burrowing wasp is flicked behind it as it excavates the nest.^[5] They nest in aggregations which may have as many as 15,000 burrows.^[4] The females hunt honeybees Apis mellifera, which are paralyzed with the sting, the female stinging the prey through the articular membranes which are situated behind the front legs, the female then carries the immobilised bee to the nest in flight between the wasp's legs. On reaching the nest she often hovers over the entrance before slowly descending into the burrow.^[4] Each brood cell is provisioned with between one and five honeybees for the larva. After the larva has fed sufficiently it spins a cocoon, the cocoon is attached to the wall of the brood cell at its base. In cooler regions the larva overwinters and the adults emerge the following summer.^[6] Other species of bee, other than honeybees, have been reported as prey including Andrena flavipes, Lasioglossum zonulus and Nomada sp in Britain^[4] as well as bees of the genera Dasypoda, Halictus and Megachile in continental Europe.^[3] Each female may collect up to 100 bees during its flight period.^[2]

The humid and warm conditions in the brood cells provide good growth conditions a number of species of mold fungi which can colonise the cells opportunistically from the surrounding soil, especially Aspergillus flavus,^[7] which can either infect the larva or the stored immobilised bees and this normally causes the larva to die. Female beewolves protect their offspring against pathogens and they have evolved strategies to reduce the mortality of their offspring in the brood cell. The first strategy is to apply copious amounts of an anti-fungal secretion from a cephalic gland on to the paralysed bees to delay fungal growth. The second strategy is that the female wasp secretes a whitish substance from specialized glands in its antennae in to the brood cell, this secretion contains symbiotic bacteria of the genus Streptomyces, which are ingested by the larva and before the larva pupates the bacteria are applied to the cocoon to protect the larva from fungal infection.^[6]

The males set up territories in vegetation near to the females' nesting aggregations, these territories do not hold any resources to interest the females.^[8] The territories are around a quarter of a square metre in extent and are marked with a pheromone from the male's cephalic glands. The males defend these territories from intruding males but the defence does not involve physical contact between the antagonists. Males may have territories which are often in close proximity to one another, constituting a form of lek, allowing the females to make their choice of mates from among the males. The males do not appear to attract the females by using any form of visual display and it is though that the females choose the males to copulate with based on the quality of the pheromones the male produces.^[6] The amount of time the male occuppies a territory is dependant on the number of female nests near that territory.^[8]

The adult wasps feed on nectar and have been recorded as feeding on nectar from bramble, sea-holly, Erica, thrift, pale toadflax Linaria repens, common ragwort, hemp-agrimony and creeping thistle.^[4]

Status in the UK

This wasp was previously considered to be one of the great aculeate rarities in Britain, with colonies only in sandy habitats on the Isle of Wight and Suffolk. It has undergone an expansion in range, with the wasp now locally common in a steadily increasing number of sites as far north as Yorkshire (2002). The species has RDB2 status (vulnerable) but, if revised, it is now likely that this status will be removed because of its increase in range and population.^[9]

References

External links

Wikimedia Commons has media related to Philanthus triangulum.

• Semiochemicals of Philanthus triangulum, the European beewolves