The leaves have only just started to open on this oak tree, a Sessile oak I think, yet it is already covered by many galls. These rounded disfigurations – called Oak apples – are caused by a tiny (5-6 mm) wasp in the family Cynipidae, called Biorhiza pallida.
It is known that the galls are caused by the injection of venom by the wingless, parthenogenetic females, which cause the newly emerged leaves to soften and swell up. These females have emerged from galls growing underground, on the roots, and they have crawled up the tree to start a new generation in the Spring. (1) The eggs hatch and the larvae secrete chemical substances which also cause the tissues to grow and form into a ball; the apple gall.
Remarkably, all of the individual wasps developing within a given gall, of which there may be as many as thirty, are of the same sex. (2) Although the gall is made of plant material, because it is induced by the wasp it is said to represent the extended phenotype of gall-wasp genes (Stone and Cook, 1998). (3)
The tree was located near the Felmersham Gravel Pits, a Site of Special Scientific Interest between the villages of Felmersham and Sharnbrook, in Bedfordshire.
The life cycle of these amazing wasps is even more complex than I have outlined here, with individual asexual females able to produce both males and females from unfertilised eggs; alternating sexual and asexual generations and way of life that utilities both the below-ground roots and above-ground shoots of the tree.
I came across this magnificent spider wasp (Pompilidae) feeding on nectar from these flowers beside the steps leading up to Wat Tham Pha Plong, Chiang Dao, Thailand. I have come across this pompilid wasp before in northern Thailand (1), but I am still not sure what species it is. With its orange antennae, it looks similar to the Australian orange spider wasp (Cryptocheilus bicolor) (2), but the head is not orange and the abdomen is black. So perhaps it is another Cryptocheilus species, of which there are twenty-four known. One website provides a check-list of pompilid species from Thailand (3), but none of these seem to fit the bill. Other sites, simply caption photos ‘Pompilidae’, so it is not one that can be identified from of the Internet. If there are any pompilid experts out there, I would love to know what it is!
Adult pompilid wasps feed on nectar, but they hunt and kill spiders to provide a food source for their off-spring. They sting and paralyse spiders and carry them off to a nest burrow, where they deposit an egg on the hapless arachnid. Each offspring has its own spider to gorge on. The wasp larva hatches out and starts feeding on the living, paralyzed spider. The bigger the spider, the more likely it is that the larvae will develop into a female wasp (which are larger than males).
I would think that there is much to learn about these wasps, particularly species which have been little studied. The are nearly all solitary wasps although a few communal, mud-nesting species exist (4). The hunting behaviour of one group of pompilids, the tarantula hawk wasps – which occur in the deserts of the USA – has been studied: “the wasp rushes at the spider, grabs a leg, flips the spider onto its back, and stings it….” The tarantulas can mount a counter attack, but it seems they are at a disadvantage and rarely succeed in killing the attacking wasp. (5) One can only wonder at how long this evolutionary battle between wasps and spiders has played out over geological time.
Some pompilid wasps are cleptoparasitoids; they steal the spider prey caught by other pompilid species. They wait until the wasp which has caught the spider puts it down and turns its attention to nest making; they then rush in and lay their own egg on the spider. This egg hatches out before the one laid by the wasp which first caught the spider, and the imposter larva eats the host egg before it hatches. (5) Very sneaky!
Some pompilids prey on species such as this orb spider, Argiope pulchella (6). The spider is sitting in the middle of an X-shaped stabilimentum; an elaborate web decoration or feature which it has constructed out of silk (below).
I don’t know how poisonous the sting of this particular wasp I photographed would be to humans; and I would not like to find out.
Pompilids are not aggressive and are usually relatively docile (unless provoked), but the sting of the closely related Tarantula hawk wasps is reportedly very intense. The pain has been described as: “like an electric wand that hits you, inducing an immediate, excruciating pain that simply shuts down one’s ability to do anything, except, perhaps, scream.” (7)
One has to admire the skill and tenacity of these wasps, which often prey on spiders which are much larger than themselves, and highly venomous. They have evolved a way of exploiting this prey source and presumably play an important role in regulating spider populations.
Butterflies, like this Clipper (Parthenos sylvia) also enjoy feeding on the flowers of this plant.
At the end of last month (on 28th August) I sat on a hillside in Galicia, Spain, next to a beautiful bush of flowering bell heather, photographing the wasps which were gorging themselves on the pollen and nectar. They were covered in pollen (below).
They were very calm and non-aggressive and I sat right next to them for some time. I did not realise at they time that I was photographing the Asian hornet or yellow-legged hornet (Vespa velutina), and not a native species.
The site was near a beautiful lookout point called Mirador do Miranda en Cariño above the town of Cariño (below).
It was only when I saw the impressive nest of this invasive species in the local museum in Ortigueira, did I realise that I had been watching the Asian hornet.
There are many different subspecies of Vespa velutina in Asia but the one that invaded Europe in 2004 and is spreading through France and Spain, is Vespa velutina nigrithorax. (1, 2). This wasp is actually smaller than the European hornet Vespa crabro, but it is a major threat to European honey bees (Apis mellifera), which unlike Asian honey bees (Apis cerana) – which evolved in the presence of this predator – do not have any defense against the Asian hornet. Our poor bees do not know how to cope with an attack by the Asian hornet. Unlike the Asian honeybees, which make a ‘very fast bee-line for the hive entrance to avoid the jinking wasps’, poor old A. mellifera ‘slows down and sashays in the face of wasps.’ (3) And although our honey bees can kill native predatory hornets by ‘heat-balling’ – surrounding them in a mass of bees – they fail to kill the Asian hornets. The Asian honey bees have ‘learnt’ how (evolved a way) to do so using a temperature higher than A. mellifera and with more balling bees. (4)
This insect was first detected in Galicia in 2013 and appears to have significantly spread and colonized new areas in the past few years. It is reassuring to see that much is being done to try to minimize the impact of this pest and there is some excellent information available online (in Spanish) including a pest management programme. (5) The widespread presence of the Asian hornet in this area is however, very worrying.
It seems that the pest is now very well established in northern Spain and is surely impossible to eradicate. In South Korea, where V. velutina also invaded and is now well established, it has rapidly displaced native hornets and become the dominant species in urban areas. (6). That is a very worrying prospect for European countries and a lot of work needs to be done, especially on the ecological effects on native species, as this Asian hornet feeds very wide range of insects, including flies, dragonflies and grasshoppers. It is really quite concerning, not just for honey bees, whose hives can be protected – by reducing the hive entrance to a narrow slit – to keep out the invasive hornet, but for native insect species.
There are some fantastic pictures of Asian hornets attacking a bee hive on this site called The Bee photographer (7).
Monceau, K., Bonnard, O., & Thiéry, D. (2014). Vespa velutina: a new invasive predator of honeybees in Europe. Journal of pest science, 87(1), 1-16.
Tan, K., Radloff, S. E., Li, J. J., Hepburn, H. R., Yang, M. X., Zhang, L. J., & Neumann, P. (2007). Bee-hawking by the wasp, Vespa velutina, on the honeybees Apis cerana and A. mellifera. Naturwissenschaften, 94(6), 469-472.
Tan, K., Wang, Z., Li, H., Yang, S., Hu, Z., Kastberger, G., & Oldroyd, B. P. (2012). An ‘I see you’prey–predator signal between the Asian honeybee, Apis cerana, and the hornet, Vespa velutina. Animal Behaviour, 83(4), 879-882.