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.
Japanese knotweed (Fallopia japonica) is a fast growing, invasive perennial with a terrible reputation for spreading and excluding other native plants. Its roots are also capable of breaking through concrete and other man-made materials (1).
But it’s not all bad! It looks quite nice when it is flower, right now in September, and it’s good for bees and insects. Another blogger beat me to the excellent title ‘knotty but nice’ (2) and there is a lot out there on the Web on it’s good-for-beeness!
There seems to be some debate on bee fora (forums) about the tastiness of Knotweed honey, which is sometimes sold as ‘bamboo honey’ in the US apparently. I’d like to try it; bet it’s nice.
Orchids flower over quite a long period, with the dates of the flowering season varying somewhat with latitude. In Scarborough, I spotted (sic) my first Common spotted orchid – in the meadows of Scarborough Castle – on the 9th June this year (2016). See below.
There must be quite a lot of individual variation between flowers, as in any population, with some flowering early and others coming along later. There is an abundance of this orchid on the slopes of North Bay, Scarborough. One of the best sites I found was behind the public lavatory on the Royal Albert Drive! There was a profusion of orchids behind the building in early July when I took these picture (they are probably still flowing there now in late July).
The Common spotted orchid flower is of course an inflorescence composed of many flowers on a spike. The individual flowers are made up of a three-lobed lip, two sepals on either side (a bit like ears!), and petals which make the hood above the reproductive bits! See below.
These orchids rely on insects to pollinate them and the red markings on the lip are thought to be guides for insects to follow, towards the source of the nectar. The plants are hermaphrodites, meaning that they have both male and female reproductive organs; there is one stamen (male) and two stigma (female) on each flower. The shape of these tiny little organs looks rather suggestive, or am I imagining it? See below.
Pyramidal orchids come into flower a bit later than Common spotted orchids. I photographed the one below in early July; it was just starting to open, from the bottom upwards.
Later on, they take on their more pyramidal shape, although they can also be quite rounded.
Small black pollen beetles can be see on one of these flowers (below).
These common but nevertheless, beautiful orchids will all too soon be over, but they are perennials, so die back down to their tubers in the ground, ready to spring up again next year. Just an everyday miracle we call Nature!
I took a few photos of a large Bombus terrestris bumblebee (queen I think) visiting foxglove flowers in St. James Park, London on a fine day last week. When I looked closely at the images I noticed a few ants within individual foxglove flowers.
Lasius niger worker ants – and other species presumably – often tend aphids on foxglove flowers (Digitalis purpurea) and may forage for nectar on the flowers (1). But ants are not always welcome visitors to the flowers; they are detrimental to their fitness for a number of reasons (2). Firstly, they are usually too small to be much good as pollinators and secondly, their aggressive behaviour may put off more useful pollinators! They are ‘nectar thieves’ taking nectar without providing any mutual benefit for the plant, and also potentially diminishing the appeal of the flower to hard-working pollinators such as bees, which might stay away. Some plants try to keep ants away by using physical or chemical barriers, or offering them an alternative source of nectar, via extrafloral nectaries – EFNs (3). Foxgloves also have guard hairs to deter smaller bees from entering the flower (4), but it seems that ants can easily pass through these.
Does the presence of the ants affect the behaviour of the bees? Bumblebees can apparently detect whether another bee has visited a particular flower recently and thereby avoid wasting time by visiting a depleted nectar source. Do they do the same with ants? Ants do leave scent markings – e.g. pheromone trails marking a source of food – and laboratory experiments have shown that bumblebees potentially could avoid ant-visited flowers (1), if they put their minds too it! But they do not seem to use this ability much in the wild. Perhaps the ants are not taking very much nectar, so it is still worthwhile for the bee to visit the flower. Also, the bumblebees are in and out so quickly, and there are so many individual flowers clustered together on a foxglove inflorescence that it is not worth taking the time to sniff out whether ants had been in or not!
Would the bumblebee avoid a flower with an ant sitting in it? Perhaps big bumblebees like this one are not bothered by ants? Or do the ants get out of their way? Anyway, my observation was that the bumblebees were in and out of the flowers so quickly it was very hard to tell whether they avoided flowers containing individual ants. Perhaps they just steam rollered over them! Someone way know the answer to this?
Ballantyne, G., & Willmer, P. (2012). Floral visitors and ant scent marks: noticed but not used?. Ecological Entomology, 37(5), 402-409.
Willmer, P.G., Nuttman, C.V., Raine, N.E., Stone, G.N., Pattrick, J.G., Henson, K. et al. (2009) Floral volatiles controlling ant behaviour. Functional Ecology, 23, 888–900.
Common vetch plants (Vicia sativa) are much favoured by ants. The reason being that they have tiny glands – called extrafloral nectaries – which produce a nectar solution which the ants imbibe. The plants provide the ants with food and in return the ants protect the plant from being eaten by other insects. A mutualistic relationship. The precise relationship is probably highly variable and undoubtedly more complex than it at first appears. If ant numbers get too high, the plant may in effect be paying too high a price for the protection it receives. Too many bodyguards! Nectar is expensive to make. And if there are no, or few threats to the plants from leaf feeding herbivores, well the plant is paying the ants for nothing. Idle bodyguards! And boy do they like their nectar!
The ants benefit in two ways: they get nectar from the plant and they also get to eat (some of) the herbivores they find on the plant. Others they just throw off the plants. More bouncers than bodyguards (or plantguards). The plant also benefits in a number of ways; it suffers less feeding damage and it sets more seeds (probably because fewer get eaten thanks to the bodyguards!).
Ants undoubtedly do their protection job well, and remove external feeders such as caterpillar larvae. When the nectaries were artificially removed from plants by scientists, the ants stayed away and the vetches suffered more leaf damage. So not surprisingly, this investment – in providing food for the ants – pays off for the plant. But there are some insects that are either too tough for the ants to remove (some weevils) or have found ways of avoiding these ‘pugnacious bodyguards’ (a wonderful terms coined by Bentley ).
The purple glandular nectaries are found on stipules which occur at the base of the leaf petiole. Ants can be seen with their heads in the hood-shaped stipules, feeding on the glands inside, in these photos which I took in Spain (Galicia). I don’t know what the ant species are, but I think this is narrow-leaved vetch (Vicia sativa ssp. nigra) which occurs in coastal areas.
Common Vetch is not a host plant for the little Wood white butterfly (Leptidea sinapis), perhaps because the ants would throw the caterpillars off the plants or eat them! But that does not stop the adults dropping in for a sip of nectar from the flower (above).
Koptur, S., & Lawton, J. H. (1988). Interactions among vetches bearing extrafloral nectaries, their biotic protective agents, and herbivores. Ecology, 278-283.
Koptur, S. (1979). Facultative mutualism between weedy vetches bearing extrafloral nectaries and weedy ants in California. American Journal of Botany, 1016-1020.
Koptur, S., Smith, C. L., & Lawton, J. H. (1996). Effects of artificial defoliation on reproductive allocation in the common vetch, Vicia sativa (Fabaceae: Papilionoideae). American Journal of Botany, 886-889.
Bentley, B. L. (1977). Extrafloral nectaries and protection by pugnacious bodyguards. Annual Review of Ecology and Systematics, 407-427.
This beautiful insect looks like a beetle, but it is in fact a bug – a true bug as entomologists call hemipterans. It is a member of the family Scutelleridae and is commonly called a jewel bug or a metallic shield bug. The Lychee Shield Bug or Green Jewel Bug, Chrysocoris stolli, is widely distributed throughout south Asia and South East Asia: from India to the Philippines.
Despite its fabulous appearance, it is a bit of a pest, reportedly feeding on some food plants and medicinal plants (1). One of these plants – Cassia occidentalis – is an exotic and widespread weed in India, and this insect is being considered as a potential biological control agent (2).
The fact that it is called the Lychee Shield Bug suggests to me that it might be fond of supping on lychees! It feeds on a wide range of plants, including some of those that happen to be grown by man! But hey, these bugs have been around an awful lot longer than us! I came across this insect in Chiang Dao – north of Chiang Mai – in northern Thailand.
The shield-like back of the insect – with the pronounced bulge at the front of the abdomen – is seen below. They are sometimes called shield-back bugs. In jewel bugs the scutellum – small shield-like structure – has expanded to cover the whole abdomen with the wings located underneath.
For a really fantastic blog on South East Asian Scutelleridae – I’m in awe of the photography on this website – check out Spineless Wonders by David Knowles (3).
Pravesh Kumar and SC Dhiman (2013). Some Ethological Aspects of Chrysocoris Stolli Wolf (Heteroptera -Pentat Omidae –. Scutellerinae). Journal of Zoological Sciences 1(1), 8-12.
Sehgal, P. K., and S. C. Dhiman. (2015). Effect of temperature and relative humidity on the occurrence of Chrysocoris stolli Wolf (Heteroptera Pentatomidae Scutellerinae) a potential biocontrol agent of Cassia occidentalies.
Take a photograph of a flower, examine it closely – or enlarge it on a computer screen – and you will invariably find an insect lurking somewhere in the picture. This is not altogether surprising when we learn that two-thirds of flowers are pollinated by insects. To achieve this, flowers have learnt – OK evolved! – how to bribe, cajole, or trick insects into carrying out this function. Plants don’t walk, so they need animals to carry out a vital function for them; they need them to carry their sperm (in the form of pollen) to another individual where it can fuse with the eggs (ovules) of the other plant. Sex, or to give it another name: reproductive out-crossing!
Some plants self-fertilise – i.e. sperm fuses with eggs from the same flower. Dandelions are among such plants – which can produce seeds without having to be fertilised – although they can also be sexual as well, relying on being fertilised by pollen carried from one dandelion to another by insects. The photo (below) shows a dandelion head composed of dozens of tiny florets, each with pistols bearing pollen, which can be picked up by visiting insects, e.g. bees.
Some plants – the anemophilous ones, lovely word – rely on the wind to carry their pollen to another individual; but if a plant is to rely on an insect to vector its pollen, then it is going to have to have a strategy to achieve this. In practice, thousands of different strategies have evolved over time. If a flower is going to rely an insect to help it reproduce, it needs to do a number of things. First of all it needs to get the attention of the insects; most insect pollinated flowers are large and brightly coloured. Next it needs to offer some sort of inducement, usually in the form of nectar, although the pollen itself is a reward for many visitors.
A variety of different insects – e.g. bees, wasps, ants, butterflies, beetles and so on – may visit a given flower. Some may be feeding on nectar (butterflies and moths); some might be defending their sap-sucking aphids (ants); some might just be sheltering or hiding in the petals; and some may be eating the plant; but the pollinator species which is best for the plant is the one that helps it to reproduce successfully (i.e. it helps to increase the plant’s fecundity). These are the insects that the flower will evolve to attract. But not all flowers are specialists in this regard; some may be visited by a variety of pollinating bees and butterflies during the day, and by moths during the night. I wonder they ever get any sleep!
The hummingbird hawk-moth (Macroglossum stellatarum) – which has a very long proboscis – has been seen visiting the wild, Fringed Pink, Dianthus monspessulanus (1, 2). This plant has very long-tubed flowers (below) and emits a strong evening fragrance to attract the moths. It may however, not be the only flower species competing for the moth’s attention! The most attractive, and sweet-smelling flowers – to a hawk-moth’s nose that is! – will presumably get visited the most. Those flowers will be the ones which are the most fecund in the next generation, and the attractiveness to hawk-moths will continue to evolve. It is interesting that we humans also find the smell of such plants appealing; after all they are not trying to attract us! I guess it demonstrates the universality of the chemistry involved; it involves a compound called linalool, which is a common attractant for nocturnal hawk-moths (3).
Sea daffodil (Pancratium maritimum) is another flower which relies on hawk-moths for pollination (4).
Spring Squill (Scilla verna) is a plant that may be ant pollinated. Ants can sometimes be seen feeding on the ovaries (below); they can contribute to pollination by transferring pollen from one flower to another, but they can also be nectar thieves, just feeding on the nectar without carrying out any pollination services in return! (5).
An alternative strategy is of course to trick the insect into carrying out the needs of the plant. Some orchids do this by looking like bees or flies, but fascinating though this is, we will not follow this further here. Flowers providing rewards of nectar need to ensure that it is not wasted and that the pollen is successfully attached to the insects, for onward transport. All manner of devices and structures are used to make sure that the pollen is first attached – by sticking, brushing or hooking – and then successfully detached and delivered to the receptive female organ: the sticky tip of the pistil, the stigma. Some plants have even evolved ways of selecting the right sort of pollinator for their needs! For example, the guard hairs (below) on the Foxglove flower, Digitalis purpurea, have it is thought, evolved to exclude small bees, which presumably are not strong enough to push past them! The flowers are effectively selecting large bees to pollinate them, especially ones with long-tongues which can reach deep inside the flower to get the nectar (6). It is beneficial to both the bees and the flower to keep the relationship between themselves; it is a mutualistic arrangement which has evolved to suit both parties: the bees get to feed on the nectar, and the flower gets its pollen spread around in an efficient and effective manner. It would not benefit either of them if little upstarts got in and stole the pollen!
Both the ecology of pollination, and the evolution of the relationships between plants and insects, are vast and much studied subjects. All I want to do here is to illustrate by means of a few photographs, how easy it is to observe some aspects of this biological phenomenon. Most cameras allow close up photograph now, and the results are often surprisingly good – even with a relatively inexpensive camera – if one is prepared to be patient, and capture a detailed image. It is not always obvious that an insect is in the picture! Many of the photos shown here were just ones I had taken of a flower. Only afterwards, when examining the image on a computer screen, did I notice the insect! Most of the images shown here have been heavily cropped (i.e. by selecting the centre of the photo) to obtain the close up I wanted. I have also included some nice close up images of flowers without insects because I just like the shapes and appearances of these flowers. There is no end to what can be done just by taking a camera out into the garden or countryside (at the right time of year!).
Finally, just a note of caution. Hopefully this blog will have shown how dependent flowers and pollinators are on each other. Anything which affects the pollinators – and bees and butterflies are suffering in our modern world – will affect the plants too. This is particularly true in the case of specialised species, which are dependent on – i.e. adapted to – a particular type of pollinator species. The bottom line is, if the pollinator goes, the flower goes too. It’s an interdependent world and we need to take better care of it.
Willemstein, Sjoert Cornelis. An evolutionary basis for pollination ecology. Vol. 10. Brill Archive, 1987.
Sometimes when you take a photograph you only notice something unusual about it when you come to examine the image closely on the computer. I took this image of a foxglove flower – something about the inside of the flower caught my attention – but it was only when I looked closely at the image that I noticed the hairs standing up on the inside, on the lower surface. What were these for? Most things have a purpose in nature don’t they?
I little bit of Googling later, I found out that Charles Darwin had been here long before me. In his book, The effects of cross and self fertilisation in the vegetable kingdom, Darwin writes:
Humble-bees [=bumblebees] can crawl into the dependent flowers with the greatest ease, using the “hairs as footholds while sucking the honey; but the smaller bees are impeded by them, and when, having at length struggled through them, they reach the slippery precipice above, they are completely baffled.”
Scrupulous as always in referring to the contributions of others, Darwin was quoting another naturalist, a certain Thomas Belt (1832 – 1878), who was clearly no slouch when it came to observing nature (2). So it was Belt, it seems who made these observations about the hairs keeping out smaller bees and other insects. He was clearly an acute observer of the natural world. Strangely, these remarks appear to have been made in a book called, The naturalist in Nicaragua, although the actual observations were made in north Wales (2). Alfred Russel Wallace reviewed Belt’s book in 1874, and described him as “a close, an accurate, and an intelligent observer. He possesses the valuable faculty of wonder at whatever is new, or strange, or beautiful in nature; and the equally valuable habit of seeking a reason for all that he sees.”(3)
So it seems that the guard hairs deter smaller bees from entering the foxglove flower. The reason being that the flower is effectively selecting large bees to pollinate it, particularly long-tongue species, such as Bombus hortorum, which can reach deep inside the flower to get the nectar (4).
However, it seems that other bumblebees, including those with short tongues are able to collect pollen from the foxglove flower (by ‘buzzing’) although it seems that they are unable to reach far enough down to the nectar source to obtaion any nectar (5).
I also discovered a lovely poem, by a poet I had not heard of until now – called Anne Stevenson – who beautifully captures the biology of the bees and the foxglove flowers in her verses. As acute a description as that of Belt in a way.
The Miracle of the Bees and the Foxgloves
Because hairs on their speckled daybeds baffle the little bees,
Foxgloves hang their shingles out for rich bumbling hummers,
Who crawl into their tunnels-of-delight with drunken ease
(See Darwin’s pages on his foxglove summers)
Plunging over heckles caked with sex-appealing stuff,
To sip from every hooker an intoxicating liquor
That stops it propagating in a corner with itself.
And this is how the foxglove keeps its sex life in order.
Two anthers – adolescent, in a hurry to dehisce –
Let fly too soon, so pollen lies in drifts about the floor.
Along swims bumbler bee and makes an undercoat of this,
Reverses, exits, lets it fall by accident next door.
So ripeness climbs the bells of Digitalis flower by flower,
Undistracted by a mind, or a design, or by desire.
Darwin, C. R. 1876. The effects of cross and self fertilisation in the vegetable kingdom. London: John Murray.
This very strange-looking flower originates from South Asia, where it occurs from Bhutan to Bangladesh. There are more than 500 species in the genus Clerodendrum L. (Family: Lamiaceae), widely distributed in tropical and subtropical regions. Many of these small trees and shrubs are used in traditional medicine and are known to be active against ‘a wide spectrum of disorders’ possibly including HIV (1). Plants have been on this earth for very much longer than us, and have evolved ways of protecting themselves using a host of organic molecules. These same molecules could also help to protect us – from microbes, from aliments, from diseases and from cancers – if we can only find them and put them to good use.
Shrivastava, Neeta, and Tejas Patel. “Clerodendrum and heathcare: an overview.” Medicinal and aromatic plant science and biotechnology 1.1 (2007): 142-150.
I came across this amazing flower – rose of Venezuela, or rose of the jungle – in Bogor Botanical Gardens, Java, Indonesia. It originates from South America, where for millions of years it existed as understorey plant of Amazonian rain forests (endemic to Brazil, Ecuador, Honduras, Venezuela and Colombia). Once discovered by Man, it has been spread all around the globe and is now widely grown in tropical gardens. In case you fancy one, it does not like temperatures below 55 °F (13 °C) – a bit like me! – but will thrive both in full sun and in partial shade (1). It seemed to be doing very well in these botanical gardens in west Java: Peta Kebun Raya Bogor.