Spider Wasps of the Dunes

I’ve commented earlier than on the difficulties that may be attendent on figuring out spider wasps (Pompilidae), a type of teams that mix a excessive species variety with a bent to be morphologically conservative. Consequently, the taxonomic historical past of this group has been one among shifting generic ideas and ill-defined wastebaskets. Not surprisingly, one of many important victims of this uncertainty has been the sort genus Pompilus. Traditionally used to cowl a big share of all spider wasps, the identify Pompilus is now restricted to a small cluster of species inhabiting the Outdated World.

Pompilus cinereus, copyright Martin Grimm.

The genus Pompilus and its historical past have been final revised intimately by Day (1981) who recognised seven species related to kind of open, sandy habitats. Probably the most widespread and best-known of those is Pompilus cinereus, discovered over huge elements of Eurasia, Africa and Australia, typically alongside our bodies of water. This species reveals a variety of morphological variation throughout its vary however Day (1981) declared himself unable to sensibly correlate this variation with discrete populations. The likelihood stays that additional research could determine P. cinereus as a species complicated. The opposite species within the genus, P. mirandus of India and south-east Asia and 5 African species, are extra restricted in vary and little studied. Pompilus mirandus is extra tolerant of vegetated habitats than P. cinereus. Conversely, P. niveus of northern Africa is a specialist of the sand dunes of the Sahara Desert. Species of Pompilus all have a black cuticle with a masking of quick gray pubescence. Probably the most distinctive function of the genus is the possession by females of lengthy, weakly curved mandibles with a single interior tooth (different spider wasps have shorter, thicker mandibles with extra tooth). These modified mandibles are associated to their distinctive method of dealing with prey. Whereas different spider wasps will drag their spider victims backwards to their nest, females of Pompilus will elevate the spider off the bottom and run ahead whereas carrying it.

Nesting behaviour has solely been described for P. cinereus. Focused prey contains ground-running spiders resembling wolf spiders or clubionids. After a spider has been captured, paralysed and carried close to the meant nest website, it’s briefly buried within the sand whereas the feminine constructs a burrow (Day urged that this preliminary burial was to forestall the spider being stolen). The easy burrow results in a single nest cell just a few inches deep. The feminine exhumes the spider, transports it into the burrow after which lays an egg on its stomach close to the entrance of the aspect. She then closes the doorway to the burrow with sand, tamping it down securely with the top of her metasoma.

Inside the burrow, the spider begins to wake from its paralysis after just a few hours. Nevertheless, it stays in poor form: its actions are sluggish and it begins to constantly exude silk from its spinnerets. By wandering in regards to the cell on this distressed state, the spider finally ends up producing a silken purse that serves as further safety for the nest’s contents. This, in fact, consists of the wasp larva that inside a few days may have begun to feed on the trapped spider.

Although particulars of breeding behaviour haven’t been noticed for different Pompilus species, they could be anticipated to resemble P. cinereus. It could be famous, nevertheless, that the feminine of P. cinereus has a patch of flattened scales on the finish of the metasoma that’s much less developed in P. mirandus. Is that this a sign that P. mirandus is in some way much less conscientious in sealing the nest burrow than P. cinereus? When you hold a watch out within the wastelands of India, you would possibly simply be taught the reply.

REFERENCE

Day, M. C. 1981. A revision of Pompilus Fabricius (Hymenoptera: Pompilidae), with additional nomenclatural and organic issues. Bulletin of the British Museum (Pure Historical past): Entomology 42 (1): 1–42.