Wasps in the family Pompilidae are commonly called spider wasps in this section of the world (South America). Species of wasps may be referred to colloquially as marabunta or marimbondo, though these names can be generally applied to any very large stinging flying insect. The family is cosmopolitan, with some 4,200 species in four subfamilies. All species are solitary, and most capture and paralyse their prey.
Spider wasps are best distinguished from other vespoid wasps in having a transverse groove dividing the mesopleuron, a region of the thorax, into halves. Larvae can also be identified by physical examination. Females are often larger than the males, with colouring and wing appearance varying greatly among the many species, though black is the most common colour, with contrasting aposematic markings of orange, red, yellow, or white also being fairly common.
Spider wasps are long-legged, solitary wasps that are so named because they use a single spider as a host for feeding their larvae. They paralyse the spider with a venomous stinger. Once paralysed, the spider is dragged to where a nest will be built, or has already been completed.
A single egg is laid on the abdomen of the spider, and the nest is then closed.
The size of the host can influence whether the wasp will lay an egg that will develop as a male, or one that will develop into a female. In fact it has been discovered that larger preys yield the females, which are the larger of the gender.
A complex set of adult behaviour can then occur, such as spreading dirt or inspecting the area, leaving the nest site inconspicuous. When the wasp larva hatches it begins to feed on the still-living spider. After consuming the edible parts of the spider, the larva spins a silk cocoon and pupates, usually emerging as an adult following a developmental process. Some ceropalines lay the egg on a still-active spider, where it feeds externally on hemolymph.
In time that spider will die, and the mature wasp larva will then pupate. They are active in gardens with the most commonly encountered species being the Cryptocheilus bicolor. This species is a very large (up to 35 mm long) black wasp with orange wings and legs and a broad orange band around its abdomen. It holds its wings up when resting, but flicks them when it hops and runs about on its long legs.
They are often seen digging in soft sandy soil, dragging huntsman spiders along. The wasps you are most likely to see and hear are female wasps preparing nest chambers for their larvae. They dig a burrow using long spines on their front legs, then search rapidly around tree trunks and on the ground for a spider.
A small number of Spider Wasps steal spiders from each other for their own larva. This behaviour is known as klepto-parasitism.
The females can sting, but stings are not common. As they are solitary insects, spider wasps do not pose the same level of threat to humans as social species of bees, ants or wasps do. However, unlike bees, wasps can sting more than once, and do not die after stinging. The sting causes a burning pain and swelling. If stings are multiple, a more severe systemic reaction may occur.
In some individuals, wasp, bee and ant stings can cause an allergic reaction (anaphylaxis), but this is relatively uncommon. Effective treatment is available, which involves known bee/ant/wasp sting-allergy sufferers carrying a special kit when outdoors. Immunotherapy or desensitisation is also available and can reduce the severity of the allergy.
A cold pack may be used to relieve the pain of the sting. If there is evidence of a more severe reaction, or the stung victim is known to be allergic to wasp and bee venom, medical attention should be sought immediately. (Source: Wikipedia – The Free Online Encyclopedia)
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