Polistes sagittarius

Common name(s): Banded paper wasp/Banded Polistes (in Poisonous Animals of Malaysia by M. Tweedie)

This is a species with quite a wide distribution in tropical Asia, as many books on Asian insect fauna will show. However, getting a precise identification and finding detailed data and photos on this species was a nearly impossible task.

This species is recorded from much of mainland China, Hong Kong, Malaysia, Singapore and elsewhere in Asia.

An interesting about this species is that it shows strong resemblance to Vespa affinis in colour and pattern. In fact, I mistook it for Vespa affinis on many occasions. The main point to differentiate them is the body size and the length of the legs. Polistes sagittarius is noticeably more slender-bodied than Vespa affinis, and has longer legs in relation with its body size. Also, it flies with its legs clearly extended vertically downwards.

A typical Polistes sagittarius individual from Hong Kong, such as the one in the photo above, is medium-sized, averaging between 18 to 24 mm in total length. It is mostly black, with parts of the thorax and front of the head in reddish brown. The first segment of the abdomen has a small dark brown band, followed by a larger band of deep yellow. The rest of the abdomen is black, as are the legs and antennae. The wings have a dark brown tinge and are clear around the edges. Its body shape is typical of Polistes species. Specimens from Southeast Asian regions such as Singapore and Thailand are sometimes even larger (I have collected specimens in Singapore measuring 24 to 27mm), without the reddish brown on head and thorax, and a lighter yellow band (the band on individuals in Singapore can appear almost whitish under strong light). This pattern of the Southeast Asian colour form having a totally black head and thorax as opposed to parts of the head and thorax being reddish brown can also be seen in hornet species such as Vespa tropica or Vespa affinis, which this species resembles. The photos below show specimens from Singapore.

Polistes sagittarius usually flies in areas of shade, with slow flight, but seldom landing. It preys almost solely on caterpillars, and I have observed workers catching caterpillars from areas where cabbage is grown, as well as from ornamental plants grown in urban areas in Singapore. A specimen I held in captivity for a period also accepted a piece of raw chicken, which it chewed up. In Hong Kong, it is usually more commonly seen around April to October. It is fairly common in many urban and rural parts of Hong Kong; it is also the most common species in Singapore.

The nest is a typical Polistine nest, open, umbrella-shaped and usually suspended from some form of shelter. It has an excentric (inclined away from the centre, towards one side) petiole (the petiole is the "stalk" from which the nest is suspended to the surface it is built on), and so often appears slightly slanted. The nest site can vary according to region. In Hong Kong, the nest is often hung in a slightly diagonal position from a tree trunk or branch. In Singapore, nests are often built under large, broad leaves or in the dense foliage of bushes, shrubs and trees of all heights, concealed by the leaves. It is apparently quite versatile, being quite inclined to building nests in urban buildings and man-made shelters; long ago I witnessed a nest that was built in a school causing some panic after some children knocked the nest down, triggering an attack. At the time, I assumed the wasps involved were Vespa affinis, due to the colouration; I remember staring at the nest and scratching my head in confusion, wondering why Vespa affinis built nests that were open, instead of the usual large, covered, oblong nests typical of most hornets. The “dilemma” was solved when I caught two specimens and realized they were Polistines.

The colony size of this species seldom gets very large. This is possibly due to much aggression within colonies. So far, in all the colonies I relocated for observation, the females were involved in much fighting, more so than most other Polistes species I have observed. I have also seen males in Singapore defending territories around plants and fighting vigorously with other males which come close, often falling to the ground together in the process. (I have noticed that species which do not fight as vigorously within the colony usually attain far larger colony sizes.)

Above: Nest of Polistes sagittarius in Singapore. Photo copyright and courtesy of Ng Kim Tee.
Below: Nest of Polistes sagittarius in Hong Kong. Photo copyright and courtesy of Christophe Barthelemy.

I used to consider this species to be somewhat defensive, due to a few painful encounters in the past. In actual fact, it is highly tolerant people moving around the vicinity of the nest, and although any attempt to get close will be closely watched and monitored by the wasps, especially in a big colony, defensive behaviour only ensues if quick movement towards the nest is made, or the nest or a surrounding object is touched or vibrated. When this happens, unlike many other species which wildly sting whatever they can latch on to, this species often aims extremely accurately straight for the head! I have never been stung by this species on my hands or arms, it has always been right on the head! However, its small colony size and inoffensive nature if not disturbed means that its nests do not pose a threat in most cases, unless built near very crowded areas. Gardeners and landscape workers should take extra precaution, however, as this species often nests in ornamental plants.