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.
- Miyake, Takashi, Ryohei Yamaoka, and Tetsukazu Yahara. “Floral scents of hawkmoth-pollinated flowers in Japan.” Journal of Plant Research 111.2 (1998): 199-205.
Source: Butterfly Pavilion at Artis Zoo
Next time you visit a butterfly house and watch them feeding on some lovely fresh fruit, think of them forcing it down and wishing they could have some rotten fruit for a change!
The Butterfly Pavilion in Amsterdam’s Artis Zoo is one of the best butterfly houses I have seen. There are a wide range of butterfly species flying around in the large tropical house; both children and adults seemed delighted with the overall experience. Large blue morpho butterflies flap about in the hot houses, flashing their iridescent wings, and alighting on dishes of cut fruit. It is a wonderful way to get a taste of the real thing: a tropical jungle. The butterflies are also, for the most part, much easier to look at closely and photograph than in the wild. Hopefully this experience, as well as being enjoyable in itself, will engender a concern for the conservation of butterflies, particularly among children.
The Insectarium in the Amsterdam Zoo was set up by a schoolteacher called Rudolph Polak in 1898, to try to reconnect the urban population with nature (1). The only insect house older than this is in London Zoo, which dates from 1881 (1). There are now many permanent, all-year-round butterfly house exhibitions all around the world, including in colder regions of Europe and North America. For example, one site lists at least twelve places to visit and observe tropical butterflies in England alone (2). There are probably many more, and certainly hundreds of living butterfly exhibits exist around the world. Some of these establishments – like Butterfly World and London Zoo – are heavily involved in the research and conservation of invertebrates, as well in promoting education and awareness of beautiful butterflies.
Maintaining these establishments is not however, easy or cheap. The tropical flowers and plants have to be carefully looked after to create a genuine rainforest experience. What I liked about the Butterfly Pavilion at Amsterdam’s Artis Zoo, was that there were lots of butterflies – people did not have to work hard to find them – and they were for the most part, in excellent condition. No doubt they had to introduce a lot of stock to maintain this status. It may surprise people to know that the butterflies seen in these houses are supplied as pupae: shipped by air freight from all over the world. European butterfly houses are generally supplied by regulated butterfly brokers, who import over 2 million pupae per year into the European Union from all around the world: United States, El Salvador, Surinam, Ecuador Malaysia, Kenya, Philippines, Thailand, and Costa Rica (3, 5). To quote from one successful exhibitor, Butterfly World, in St Albans:
“They are bred in rainforests around the world, on farms staffed by locals who breed multigenerational butterflies in captivity, therefore not affecting the indigenous ecosystem. This type of farming treats rainforest as a sustainable resource, rather than allowing the land to be cleared. A positive aspect of tropical butterfly farms stems from their interaction with the country and people. Areas of tropical land that might otherwise be deforested can be protected whilst the land produces value through breeding and trade of tropical butterflies. In many cases the local population is quite poor, so the farms also provide employment and income.” (4)
The growing popularity of butterfly houses such as this have generated what Boppré and Vane-Wright – in an excellent 2012 paper on this subject – have called a global ‘Butterfly House Industry’ (5). In other words, there is now a mass production of butterfly pupae to supply the demand. This production generally consist of about 50 popular species from the families Nymphalidae (notably Danaus, Idea, Morpho, Caligo, Cethosia, Heliconius, Hypolimnas, Parthenos), Papilionidae (Papilio) and a small number of Pieridae (5). These are generally large and colourful species that can be mass reared, successfully shipped, and relied on to fly about in butterfly houses! But they represent only a tiny fraction of the c. 20,000 butterfly species known, and most butterfly families are not represented. These glamorous butterflies are in effect the honorary representatives for butterflies as a whole, and perhaps the flagships for the insects generally. Large beetles, stick and leaf insects are also quite popular in some zoos, but it is butterflies that people pay to see!
There are controversial issues with this industry, for example to do with fair trade, animal husbandry and the use of wildlife for entertainment: which are discussed in detail by Boppré and Vane-Wright (2012). It seems to me that if we are going to run these multimillion pound/dollar facilities, then it has to be for more than just entertainment and novelty value. Profits must be ploughed back into insect conservation, and the opportunity for education about the status and threats to butterflies in the wild needs to be exploited.
Turning to the stars of the show, Morpho peleides butterflies often gather together in groups (‘mobbing’), apparently to deter their predators; perhaps all those eye spots look intimidating! Interestingly, as Boppré and Vane-Wright point out, fruit-eating butterflies like these morphos really need rotten fruit, but since this ‘supposedly upsets the aesthetic sense of visitors to live butterfly exhibits….‘fresh’ fruit is often offered instead” (5). They rightly point out that it would be better to enlighten people about the real needs of the butterflies. So next time you visit a butterfly house and watch them feeding on some lovely fresh fruit, think of them forcing it down and wishing they could have some rotten fruit for a change!
- Resh, Vincent H., and Ring T. Cardé, eds. Encyclopedia of insects. Academic Press, 2009.
- Boppré, Michael, and R. I. Vane-Wright. “The butterfly house industry: conservation risks and education opportunities.” Conservation and Society 10.3 (2012): 285.
Source: Little beggars! Turnstones waiting in a car park in Scarborough for some scraps!
Turnstones (Arenaria interpres) are a common sight all around the harbour, during the winter, in Scarborough. Many of them have been fitted with coloured leg rings and flags (PVC) which is part of an ornithological study to investigate where they migrate to in the summer. Turnstones which have been ringed in Great Britain & Ireland have been recovered, i.e. found and released again, in Greenland, Iceland, Scandinavia and all the way down the coasts of western Europe and West Africa (1).
Anyway, the ones that live in Scarborough during the winter are quite tame, and like to hang around the car parks near the pier waiting for people to throw scraps – the remains of their pasties or fish and chip lunches! – out of the car window. When a car door opens, they rush over to see if anything edible is being tossed out! It often is. In the meantime, they were waiting in a space, enjoying the winter sun. I liked the way they cast a shadow in the afternoon light.
Quite a few of them had rings and flags. They carry these little coloured markers with them on their journeys across the world. According to the British Trust for Ornithology, a bird with a coloured ring is a bit like wearing a watch is for us! (2) A bit like wearing a Swatch watch I expect! Well maybe, but bird rings are not totally without effects. Some studies have demonstrated problems caused by plastic rings (3). They are however, mostly benign and generate a lot of useful information which benefits the species in terms of conservation and knowledge. So these little beggars will have to keep wearing their coloured watches for a while yet!
- Griesser, Michael, et al. “Causes of ring-related leg injuries in birds–evidence and recommendations from four field studies.” PloS one 7.12 (2012): e51891.