Hunting strategies used by wasps

There are several publications covering the hunting strategies of various wasps, although most of these are research papers and not widely available. In this section, I shall describe some interesting hunting methods I have seen employed by several species of wasps.

In general, the hunting process is fairly simple; the wasp actively searches throughout vegetation for prey. When she locates it, she pounces straight on it, and either kills it by biting and chewing (in the case of social wasps; they only occasionally use their sting to subdue large prey) or sting to paralyse it (solitary wasps). However, many species of wasps have more varied methods of obtaining their prey.

Between the two main groups, the solitary wasps generally have more simple hunting strategies, and usually use similar methods as the one described above. However, a couple of Bembix species (digger wasps of the genus Sphecidae) are known to hunt flies. I personally observed two species in Singapore, and I remember once thinking that these wasps surely had some sort of hunting strategy, due to their fast, agile flight and the quick, alert nature of their prey. I was fortunate enough to witness this first-hand on a recent trip back to Singapore.

These wasps would sometimes appear around rubbish bins or barbecue sites. They would often use corners of such objects or walls to stalk their prey, possibly to avoid being detected. When she got close enough, the wasp would suddenly attack, easily bringing an unsuspecting fly down!

Besides houseflies (Muscidae) and "greenbottle" or fleshfly types (Calliphoridae), these wasps also hunted hoverflies (Syrphidae) on grassy areas near the sea. In the afternoon and evening, many of these flies could be seen feeding from flowers or resting on blades of long grass. The wasp would fly low through the grass, and then attack from below, catching the fly completely by surprise.

Among the social wasps, the paper wasps such as Polistes and Parapolybia also adopt simple methods of flying around bushes and shrubs, and thoroughly checking for prey on the undersides of leaves. It is the various species of Vespa (hornets) which have some rather unique and amazing hunting strategies.

The hornets do also employ the simple method described above. But they also use many other methods, some of them rather tricky, others requiring superb flight skills. The methods employed are usually in line with the build, speed and flight mannerism of the species in question. For instance, Vespa affinis (lesser banded hornet) is a small to medium-sized hornet, with flight of only average speed. Therefore, it usually hunts like most paper wasps or solitary wasps, flying low among grass and shrubs in search of prey. However, I witnessed some individuals on a Singapore beach around dead mussels washed up on the shore. At first, I guessed that they were collecting meat from the mussels, but apparently the rotten shellfish held no interest for them at all. Instead, they positioned themselves inside the shells. When flies, atttracted by the stench, tried to enter, they were immediately grabbed by the waiting hornets and taken away.

Vespa velutina is a similar-sized hornet, with some similarities to the former species, in that it is also a small to medium-sized species, widely distributed, and generally nests high in trees. However, the flight of Vespa velutina is entirely different. This species is probably one of the most advanced and efficient predators in the wasp world, employing many different strategies. It has excellent flight skills, and can hover for long periods. When it pounces, it misses least frequently among the hornets I have observed in Hong Kong.

Vespa velutina frequently attacks a species of dragonfly, Pantala flavescens. This dragonfly frequently congregates and flies in large numbers during warm, humid weather, seldom landing. The wasp always attacks either from a strategic location or seemingly out of nowhere. She rushes into the swarm of dragonflies, and chases them in turn relentlessly, until she catches hold of one and brings it crashing down. The dragonflies are extremely fast flyers, but the rate of success is surprisingly high. If she fails to catch any after some time, the hornet simply flies off to another location, such as the top of a tree, and wait till the swarm settles down, then attacks again, this time from another direction.

Another technique frequently utilized by Vespa velutina again involves some foul substance, such as a dead animal, dung or rotting meat. Unlike Vespa affinis, Vespa velutina hovers in a clearing, seldom landing. She often does not immediately strike, but waits till there is a substantial congregation of flies, before pouncing on each one in turn.

The small, yellow coloured hornet Vespa bicolor also employs such ambush tactics. However, this species does not usually hover or lurk in the cover of vegetation. The wasp instead frequently stands on a heap of dog droppings! She waits till a fly comes within range, then strikes. Vespa bicolor can be seen around dog dung everywhere in Hong Kong during the autumn and winter, and many people mistakenly assumed the wasp was eating the dung! Vespa bicolor is generally not as successful as Vespa velutina in catching flies. However, it is still a fairly swift species and frequently brings down bees and butterflies by active hunting around flowers in gardens and urban parks.

The swift-flying hornets also frequently prey on honeybees near the nest. I have witnessed this on several occasions, and it is quite amazing. The hornet lingers around the nest entrance, hovering while facing the entrance. The bees respond by emerging in large numbers and vibrating or "tremoring" as one. This is a most spectacular sight; a wave of movement can be seen through the carpet of bees, which serve as a protective platform for the foragers leaving and returning. As long as they keep close to the mass of guard bees, they are safe, since the hornet cannot get too close; the bees will quickly swarm over the hornet and kill her if that happens. However, the hornet eventually manages to intercept a bee and quickly makes off with her catch. I have witnessed this with Vespa bicolor and Vespa velutina in Hong Kong. Other species known to use this tactic include Vespa multimaculata from Southeast Asia and Vespa simillima in Japan. I have even seen a video clip of Vespa ducalis doing this, although it is not small and fast-flying like other hornets which usually use this method!

One of the best-known hunting strategies of hornets involves Vespa mandarinia, and also Vespa soror. This species, besides being the largest known hornet species, is also able to launch coordinated attacks on the nests of honeybees and even other social wasps and smaller hornets. They attack in groups of up to 30 or more, and can totally annihilate a whole colony of bees in mere hours. They are also known to attack the nests of yellowjackets (Vespula species) and the yellow hornet Vespa simillima.

When a social wasp kills prey larger than herself, she generally bites part of the meat out and brings it back to the nest. When this happens, she usually circles the area and the kill several times before flying off; this is probably to orientate and to "memorize" how to return to the spot. Minutes later, depending on how far the nest is from the kill, she will return, and cut out more of the insect to bring back. The wasp may make several trips back and forth, depending on how big the prey is.

Sometimes, the kill is stolen by other foraging wasps. These are usually species which frequently use freshly dead meat, not necessary killed by themselves. For instance, Vespa affinis and Polistes olivaceus frequently kill very large caterpillars in Hong Kong. It is not uncommon for them to bring a small part of the prey back, and return only to find other wasps biting at their kill. However, if the prey is large enough, there is usually minimal squabbling. I frequently see two or three Vespa affinis and Polistes olivaceus hard at work cutting the flesh off a huge caterpillar. Often, the opportunistic Parapolybia, which frequently feed on carrion, will quickly arrive to an insect killed by one of the other wasps. By the time the original hunter returns, the kill is already surrounded by Parapolybia, all taking small bits of flesh away. However, the original hunter is usually content to simply reclaim her corner and work at taking more meat away, seemingly ignorant of the small wasps biting at the other end.

Vespa bicolor, besides being an adaptable scavenger and hunter, is also an adept thief! I have frequently observed workers of this species wait in areas where the dragonfly Pantala flavescens is plentiful. Workers of Vespa velutina hunt these dragonflies with spectacular aerial chases, as described above. Vespa bicolor frequently loiters unnoticed, till a dragonfly is brought down and killed. The loitering wasp waits for the Vespa velutina worker to fly away with part of the kill, and then quickly moves in and steals part of the kill for herself.

Stealing prey from spider webs is another tactic frequently employed by various wasps. In Hong Kong, I occasionally see Vespa affinis, Vespa velutina, Vespa soror and the three species of Parapolybia do this. They usually rely on sight for this. Web-building spiders sometimes wrap up their prey and leave it in the web for later consumption if they are not hungry. The wasp will frequently strike straight at this prey, bite at the web to dislodge it and take it away. It is interesting to note that the wasp almost never gets caught by the spider web.

Although often successful in obtaining food from spider webs, the manner employed by the above-mentioned species must seem crude when compared to Stenogastrine wasps. These extremely slender tropical wasps fly soundlessly, and although they seem delicate, they are actually skilled flyers, and are able to hover and even fly backwards in mid-air. Not much has been written on their feeding habits. In Singapore, I have witnessed them catch small flies and mosquitoes on several occasions, but more often see them stealing food from spider webs. In fact, watching the way they go about doing it, it seems that they are quite specialised in this aspect and are perfectly adapted to do so! The way they hover cautiously, keeping an eye on the spider and careful not to draw its attention while scrutinizing the assorted items stuck in the web, it is totally different from the rough manner of other wasps, which simply crash into the web and remove prey. When a forager finds something of interest to her, she hovers near it, getting closer and closer all the while. She then lands with her legs latched onto this prey item, while somehow keeping her abdomen and the rest of the body clear of the web! These wasps can even maneuver with ease through all the gaps in the web. Finally, the wasp pulls the item out of the web, and then seemingly disappears! These wasps seem to target very small items, probably due to their size and slender build. They usually remove objects without the spider even noticing. I have also seen these wasps display incredible attempts to distract the spider, first flying to another side of the web away from the prey and carefully plucking at the web to attract the spider's attention, then gliding back to claim the prize while the spider is still busy trying to find out the source of movement! Finally, I have also seen on three occasions small spiders being caught straight out of the web and killed by these wasps!

For more info on foraging behaviour of solitary wasps, I recommend the following article: Social Wasp (Hymenoptera: Vespidae) Foraging Behaviour; M. Raveret Richter, Annual Review of Entomology, 2000, Volume 45: 121-150